2009 Vol. 26, No. 4
Display Method:
2009, 26(4): 614-620.
doi: 10.1007/s00376-009-8011-0
Abstract:
Based on reconstructions of precipitation events from the rain and snowfall archives of the Qing Dynasty (1736--1911), the drought/flood index data mainly derived from Chinese local gazettes from 1736--2000, and the observational data gathered since 1951, the spatial patterns of monsoon rainbands are analyzed at different time scales. Findings indicate that monsoon rainfall in northern China and the middle-lower reaches of the Yangtze River have significant inter-annual (e.g., 5--7-yr and 2--4-yr) as well as inter-decadal (e.g., 20--30-yr and quasi-10-yr) fluctuation signals. The spatial patterns in these areas also show significant cycles, such as on a 60--80-yr time scale, a reversal phase predominates the entire period from 1736--2000; on a quasi-30-yr time scale, a consistent phase was prevalent from 1736 to 2000; and on a 20-yr time scale, the summer monsoon rains show different spatial patterns before and after 1870.
Based on reconstructions of precipitation events from the rain and snowfall archives of the Qing Dynasty (1736--1911), the drought/flood index data mainly derived from Chinese local gazettes from 1736--2000, and the observational data gathered since 1951, the spatial patterns of monsoon rainbands are analyzed at different time scales. Findings indicate that monsoon rainfall in northern China and the middle-lower reaches of the Yangtze River have significant inter-annual (e.g., 5--7-yr and 2--4-yr) as well as inter-decadal (e.g., 20--30-yr and quasi-10-yr) fluctuation signals. The spatial patterns in these areas also show significant cycles, such as on a 60--80-yr time scale, a reversal phase predominates the entire period from 1736--2000; on a quasi-30-yr time scale, a consistent phase was prevalent from 1736 to 2000; and on a 20-yr time scale, the summer monsoon rains show different spatial patterns before and after 1870.
2009, 26(4): 621-629.
doi: 10.1007/s00376-009-9028-0
Abstract:
We present a composite tree-ring chronology from two sites of Qilian Juniper (Sabina przewalskii) in the northwestern Qilian Mountains (QM), Northwestern China. Precipitation in June was found to be the main limiting factor for tree-growth. The tree rings are also significantly and positively correlated with June precipitation over large areas of the northern Tibetan Plateau (TP). The authors thus consider that the tree-ring based drought reconstruction from 1803--2006 is representative of a large area drought history. During the reconstruction period, persistent and severe dry epochs occurred in the 1820s--1830s, 1870s--1880s, 1920s, and 1950s--1960s, and persistent wet periods were found from 1803--1810s, 1890s--1920s, and 1970s--1980s. The severe dry and wet periods are similar to those found over the northeastern TP, indicating the potential linkages of the drought regimes between them. Comparison with global SST indicates that the drought variability is closely related to the tropical Pacific and Arctic Ocean SSTs, suggesting the connection of regional moisture variations to the Asian monsoon and westerly belt circulations, respectively.
We present a composite tree-ring chronology from two sites of Qilian Juniper (Sabina przewalskii) in the northwestern Qilian Mountains (QM), Northwestern China. Precipitation in June was found to be the main limiting factor for tree-growth. The tree rings are also significantly and positively correlated with June precipitation over large areas of the northern Tibetan Plateau (TP). The authors thus consider that the tree-ring based drought reconstruction from 1803--2006 is representative of a large area drought history. During the reconstruction period, persistent and severe dry epochs occurred in the 1820s--1830s, 1870s--1880s, 1920s, and 1950s--1960s, and persistent wet periods were found from 1803--1810s, 1890s--1920s, and 1970s--1980s. The severe dry and wet periods are similar to those found over the northeastern TP, indicating the potential linkages of the drought regimes between them. Comparison with global SST indicates that the drought variability is closely related to the tropical Pacific and Arctic Ocean SSTs, suggesting the connection of regional moisture variations to the Asian monsoon and westerly belt circulations, respectively.
2009, 26(4): 630-641.
doi: 10.1007/s00376-009-8213-5
Abstract:
Climate in mainland China can be divided into the monsoon region in the southeast and the westerly region in the northwest as well as the intercross zone, i.e., the monsoon northernmost marginal active zone that is oriented from Southwest China to the upper Yellow River, North China, and Northeast China. In the three regions, dry-wet climate changes are directly linked to the interaction of the southerly monsoon flow on the east side of the Tibetan Plateau and the westerly flow on the north side of the Plateau from the inter-annual to inter-decadal timescales. Some basic features of climate variability in the three regions for the last half century and the historical hundreds of years are reviewed in this paper. In the last half century, an increasing trend of summer precipitation associated with the enhancing westerly flow is found in the westerly region from Xinjiang to northern parts of North China and Northeast China. On the other hand, an increasing trend of summer precipitation along the Yangtze River and a decreasing trend of summer precipitation along the monsoon northernmost marginal active zone are associated with the weakening monsoon flow in East Asia. Historical documents are widely distributed in the monsoon region for hundreds of years and natural climate proxies are constructed in the non-monsoon region, while two types of climate proxies can be commonly found over the monsoon northernmost marginal active zone. In the monsoon region, dry-wet variation centers are altered among North China, the lower Yangtze River, and South China from one century to another. Dry or wet anomalies are firstly observed along the monsoon northernmost marginal active zone and shifted southward or southeastward to the Yangtze River valley and South China in about a 70-year timescale. Severe drought events are experienced along the monsoon northernmost marginal active zone during the last 5 centuries. Inter-decadal dry-wet variations are depicted by natural proxies for the last 4--5 centuries in several areas over the non-monsoon region. Some questions, such as the impact of global warming on dry-wet regime changes in China, complex interactions between the monsoon and westerly flows in Northeast China, and the integrated multi-proxy analysis throughout all of China, are proposed.
Climate in mainland China can be divided into the monsoon region in the southeast and the westerly region in the northwest as well as the intercross zone, i.e., the monsoon northernmost marginal active zone that is oriented from Southwest China to the upper Yellow River, North China, and Northeast China. In the three regions, dry-wet climate changes are directly linked to the interaction of the southerly monsoon flow on the east side of the Tibetan Plateau and the westerly flow on the north side of the Plateau from the inter-annual to inter-decadal timescales. Some basic features of climate variability in the three regions for the last half century and the historical hundreds of years are reviewed in this paper. In the last half century, an increasing trend of summer precipitation associated with the enhancing westerly flow is found in the westerly region from Xinjiang to northern parts of North China and Northeast China. On the other hand, an increasing trend of summer precipitation along the Yangtze River and a decreasing trend of summer precipitation along the monsoon northernmost marginal active zone are associated with the weakening monsoon flow in East Asia. Historical documents are widely distributed in the monsoon region for hundreds of years and natural climate proxies are constructed in the non-monsoon region, while two types of climate proxies can be commonly found over the monsoon northernmost marginal active zone. In the monsoon region, dry-wet variation centers are altered among North China, the lower Yangtze River, and South China from one century to another. Dry or wet anomalies are firstly observed along the monsoon northernmost marginal active zone and shifted southward or southeastward to the Yangtze River valley and South China in about a 70-year timescale. Severe drought events are experienced along the monsoon northernmost marginal active zone during the last 5 centuries. Inter-decadal dry-wet variations are depicted by natural proxies for the last 4--5 centuries in several areas over the non-monsoon region. Some questions, such as the impact of global warming on dry-wet regime changes in China, complex interactions between the monsoon and westerly flows in Northeast China, and the integrated multi-proxy analysis throughout all of China, are proposed.
2009, 26(4): 642-655.
doi: 10.1007/s00376-009-9010-x
Abstract:
The climatological characteristics of the moisture budget over the joining area of Asia and the Indian-Pacific Ocean (AIPO) and its adjacent regions as well as their anomalies have been estimated in this study. The main results are as follows. In the winter, the northeasterly moisture transport covers the extensive areas at the lower latitudes of the AIPO. The westerly and northerly moisture transport is the major source and the South Indian Ocean (SIO) is the moisture sink. In the summer, influenced by the southwesterly monsoonal wind, the cross-equatorial southwesterly moisture transport across Somali originating from the SIO is transported through the Arabian Sea (AS), the Bay of Bengal (BOB), and the South China Sea (SCS) to eastern China. The AIPO is controlled by the southwesterly moisture transport. The net moisture influx over the AIPO has obvious interannual and interdecadal variations. From the mid- or late 1970s, the influxes over the SIO, the AS, the northern part of the western North Pacific (NWNP), and North China (NC) as well as South China (SC) begin to decrease abruptly, while those over Northeast China (NEC) and the Yangtze River-Huaihe River basins (YHRB) have increased remarkably. As a whole, the net moisture influxes over the BOB and the southern part of the western North Pacific (SWNP) in the recent 50 years take on a linear increasing trend. However, the transition timing for these two regions is different with the former being at the mid- or late 1980s and the latter occurring earlier, approximately at the early stage of the 1970s. The anomalous moisture source associated with the precipitation anomalies is different from the normal conditions of the summer precipitation. For the drought or flood years or the years of El Ni\~no and its following years, the anomalous moisture transport originating from the western North Pacific (WNP) is the vital source of the anomalous precipitation over eastern China, which is greatly related with the variation of the subtropical Pacific high.
The climatological characteristics of the moisture budget over the joining area of Asia and the Indian-Pacific Ocean (AIPO) and its adjacent regions as well as their anomalies have been estimated in this study. The main results are as follows. In the winter, the northeasterly moisture transport covers the extensive areas at the lower latitudes of the AIPO. The westerly and northerly moisture transport is the major source and the South Indian Ocean (SIO) is the moisture sink. In the summer, influenced by the southwesterly monsoonal wind, the cross-equatorial southwesterly moisture transport across Somali originating from the SIO is transported through the Arabian Sea (AS), the Bay of Bengal (BOB), and the South China Sea (SCS) to eastern China. The AIPO is controlled by the southwesterly moisture transport. The net moisture influx over the AIPO has obvious interannual and interdecadal variations. From the mid- or late 1970s, the influxes over the SIO, the AS, the northern part of the western North Pacific (NWNP), and North China (NC) as well as South China (SC) begin to decrease abruptly, while those over Northeast China (NEC) and the Yangtze River-Huaihe River basins (YHRB) have increased remarkably. As a whole, the net moisture influxes over the BOB and the southern part of the western North Pacific (SWNP) in the recent 50 years take on a linear increasing trend. However, the transition timing for these two regions is different with the former being at the mid- or late 1980s and the latter occurring earlier, approximately at the early stage of the 1970s. The anomalous moisture source associated with the precipitation anomalies is different from the normal conditions of the summer precipitation. For the drought or flood years or the years of El Ni\~no and its following years, the anomalous moisture transport originating from the western North Pacific (WNP) is the vital source of the anomalous precipitation over eastern China, which is greatly related with the variation of the subtropical Pacific high.
2009, 26(4): 656-665.
doi: 10.1007/s00376-009-0920-8
Abstract:
The authors have developed an integral view of the inter-decadal variability of July--August (JA) tropospheric temperature across the entire subtropical Northern Hemisphere. Using reanalysis data and complementary balloon-borne measurements, the authors identify one major mode of variability for the period 1958--2001 which exhibits a significant cooling center over East Asia and warming centers over the North Atlantic and North Pacific. The cooling (warming) signals barotropically penetrate through the troposphere, with the strongest anomalies at 200--300 hPa. The amplitude of the cooling over East Asia is stronger than that of the warming over the North Atlantic (North Pacific) by a factor of 2 (3). This dominant mode exhibits a declining tendency for the entire period examined, particularly before 1980. After the mid-1980s, the tendency has leveled off. Variations of the harmonious change of JA upper tropospheric temperature represented by the principal component of Empirical Orthogonal Function analysis exhibit significant negative (positive) correlations with SST anomalies in the eastern tropical Pacific and the western tropical Indian Ocean (mid-latitude North Pacific). Possible mechanisms are discussed.
The authors have developed an integral view of the inter-decadal variability of July--August (JA) tropospheric temperature across the entire subtropical Northern Hemisphere. Using reanalysis data and complementary balloon-borne measurements, the authors identify one major mode of variability for the period 1958--2001 which exhibits a significant cooling center over East Asia and warming centers over the North Atlantic and North Pacific. The cooling (warming) signals barotropically penetrate through the troposphere, with the strongest anomalies at 200--300 hPa. The amplitude of the cooling over East Asia is stronger than that of the warming over the North Atlantic (North Pacific) by a factor of 2 (3). This dominant mode exhibits a declining tendency for the entire period examined, particularly before 1980. After the mid-1980s, the tendency has leveled off. Variations of the harmonious change of JA upper tropospheric temperature represented by the principal component of Empirical Orthogonal Function analysis exhibit significant negative (positive) correlations with SST anomalies in the eastern tropical Pacific and the western tropical Indian Ocean (mid-latitude North Pacific). Possible mechanisms are discussed.
2009, 26(4): 666-678.
doi: 10.1007/s00376-009-9009-3
Abstract:
In our previous study, a statistical linkage between the spring Arctic sea ice concentration (SIC) and the succeeding Chinese summer rainfall during the period 1968--2005 was identified. This linkage is demonstrated by the leading singular value decomposition (SVD) that accounts for 19% of the co-variance. Both spring SIC and Chinese summer rainfall exhibit a coherent interannual variability and two apparent interdecadal variations that occurred in the late 1970s and the early 1990s. The combined impacts of both spring Arctic SIC and Eurasian snow cover on the summer Eurasian wave train may explain their statistical linkage. In this study, we show that evolution of atmospheric circulation anomalies from spring to summer, to a great extent, may explain the spatial distribution of spring and summer Arctic SIC anomalies, and is dynamically consistent with Chinese summer rainfall anomalies in recent decades. The association between spring Arctic SIC and Chinese summer rainfall on interannual time scales is more important relative to interdecadal time scales. The summer Arctic dipole anomaly may serve as the bridge linking the spring Arctic SIC and Chinese summer rainfall, and their coherent interdecadal variations may reflect the feedback of spring SIC variability on the atmosphere. The summer Arctic dipole anomaly shows a closer relationship with the Chinese summer rainfall relative to the Arctic Oscillation.
In our previous study, a statistical linkage between the spring Arctic sea ice concentration (SIC) and the succeeding Chinese summer rainfall during the period 1968--2005 was identified. This linkage is demonstrated by the leading singular value decomposition (SVD) that accounts for 19% of the co-variance. Both spring SIC and Chinese summer rainfall exhibit a coherent interannual variability and two apparent interdecadal variations that occurred in the late 1970s and the early 1990s. The combined impacts of both spring Arctic SIC and Eurasian snow cover on the summer Eurasian wave train may explain their statistical linkage. In this study, we show that evolution of atmospheric circulation anomalies from spring to summer, to a great extent, may explain the spatial distribution of spring and summer Arctic SIC anomalies, and is dynamically consistent with Chinese summer rainfall anomalies in recent decades. The association between spring Arctic SIC and Chinese summer rainfall on interannual time scales is more important relative to interdecadal time scales. The summer Arctic dipole anomaly may serve as the bridge linking the spring Arctic SIC and Chinese summer rainfall, and their coherent interdecadal variations may reflect the feedback of spring SIC variability on the atmosphere. The summer Arctic dipole anomaly shows a closer relationship with the Chinese summer rainfall relative to the Arctic Oscillation.
2009, 26(4): 679-691.
doi: 10.1007/s00376-009-8188-2
Abstract:
In order to provide high quality data for climate change studies, the data quality of turbulent flux measurements at the station of SACOL (Semi-Arid Climate & Environment Observatory of Lanzhou University), which is located on a semi-arid grassland over the Loess Plateau in China, has been analyzed in detail. The effects of different procedures of the flux corrections on CO2, momentum, and latent and sensible heat fluxes were assessed. The result showed that coordinate rotation has a great influence on the momentum flux but little on scalar fluxes. For coordinate rotation using the planar fit method, different regression planes should be determined for different wind direction sectors due to the heterogeneous nature of the ground surface. Sonic temperature correction decreased the sensible heat flux by about 9%, while WPL correction (correction for density fluctuations) increased the latent heat flux by about 10%. WPL correction is also particularly important for CO2 fluxes. Other procedures of flux corrections, such as the time delay correction and frequency response correction, do not significantly influence the turbulent fluxes. Furthermore, quality tests on stationarity and turbulence development conditions were discussed. Parameterizations of integral turbulent characteristics (ITC) were tested and a specific parameterization scheme was provided for SACOL. The ITC test on turbulence development conditions was suggested to be applied only for the vertical velocity. The combined results of the quality tests showed that about 62%--65% of the total data were of high quality for the latent heat flux and CO2 flux, and as much as about 76% for the sensible heat flux. For the momentum flux, however, only about 35% of the data were of high quality.
In order to provide high quality data for climate change studies, the data quality of turbulent flux measurements at the station of SACOL (Semi-Arid Climate & Environment Observatory of Lanzhou University), which is located on a semi-arid grassland over the Loess Plateau in China, has been analyzed in detail. The effects of different procedures of the flux corrections on CO2, momentum, and latent and sensible heat fluxes were assessed. The result showed that coordinate rotation has a great influence on the momentum flux but little on scalar fluxes. For coordinate rotation using the planar fit method, different regression planes should be determined for different wind direction sectors due to the heterogeneous nature of the ground surface. Sonic temperature correction decreased the sensible heat flux by about 9%, while WPL correction (correction for density fluctuations) increased the latent heat flux by about 10%. WPL correction is also particularly important for CO2 fluxes. Other procedures of flux corrections, such as the time delay correction and frequency response correction, do not significantly influence the turbulent fluxes. Furthermore, quality tests on stationarity and turbulence development conditions were discussed. Parameterizations of integral turbulent characteristics (ITC) were tested and a specific parameterization scheme was provided for SACOL. The ITC test on turbulence development conditions was suggested to be applied only for the vertical velocity. The combined results of the quality tests showed that about 62%--65% of the total data were of high quality for the latent heat flux and CO2 flux, and as much as about 76% for the sensible heat flux. For the momentum flux, however, only about 35% of the data were of high quality.
2009, 26(4): 692-700.
doi: 10.1007/s00376-009-8198-0
Abstract:
data from july 2006 to june 2008 observed at sacol (semi-arid climate and environment observatory of lanzhou university, 35.946oN, 104.137oE, elev. 1961 m), a semi-arid site in northwest china, are used to study seasonal variability of soil moisture, along with surface albedo and other soil thermal parameters, such as heat capacity, thermal conductivity and thermal diffusivity, and their relationships to soil moisture content. the results indicate that surface albedo decreases with increases in soil moisture content, showing a typical exponential relation between the surface albedo and the soil moisture. the heat capacity, the soil thermal diffusivity, and soil thermal conductivity show large variations between julian day 90--212 and 450--578. the soil thermal conductivity is found to increase as a power function of soil moisture. soil heat capacity and soil thermal diffusivity increase with increases in soil moisture. the sacol observed soil moisture are also used to validate the amsr-e/aqua retrieved soil moisture and there is good agreement between them. the analysis of the relationship between satellite retrieved soil moisture and precipitation suggests that the variability of soil moisture depends on the variation of precipitation over the loess plateau.
data from july 2006 to june 2008 observed at sacol (semi-arid climate and environment observatory of lanzhou university, 35.946oN, 104.137oE, elev. 1961 m), a semi-arid site in northwest china, are used to study seasonal variability of soil moisture, along with surface albedo and other soil thermal parameters, such as heat capacity, thermal conductivity and thermal diffusivity, and their relationships to soil moisture content. the results indicate that surface albedo decreases with increases in soil moisture content, showing a typical exponential relation between the surface albedo and the soil moisture. the heat capacity, the soil thermal diffusivity, and soil thermal conductivity show large variations between julian day 90--212 and 450--578. the soil thermal conductivity is found to increase as a power function of soil moisture. soil heat capacity and soil thermal diffusivity increase with increases in soil moisture. the sacol observed soil moisture are also used to validate the amsr-e/aqua retrieved soil moisture and there is good agreement between them. the analysis of the relationship between satellite retrieved soil moisture and precipitation suggests that the variability of soil moisture depends on the variation of precipitation over the loess plateau.
2009, 26(4): 701-706.
doi: 10.1007/s00376-009-9035-1
Abstract:
This paper investigates the variability of the break-up dates of the rivers in Northeast China from their icebound states for the period of 1957--2005 and explores some potential explanatory mechanisms. Results show that the break-up of the two major rivers (the Heilongjiang River and Songhuajiang River) was about four days earlier, and their freeze-up was about 4--7 days delayed, during 1989--2005 as compared to 1971--1987. This interdecadal variation is evidently associated with the warming trend over the past 50 years. In addition, the break-up and freeze-up dates have large interannual variability, with a standard deviation of about 10--15 days. The break-up date is primarily determined by the January--February--March mean surface air temperature over the Siberian-Northeast China region via changes in the melting rate, ice thickness, and snow cover over the ice cover. The interannual variability of the break-up date is also significantly connected with the Northern Annular Mode (NAM), with a correlation coefficient of 0.35--0.55 based on the data from four stations along the two rivers. This relationship is attributed to the fact that the NAM can modulate the East Asian winter monsoon circulation and Siberian-Northeast China surface air temperature in January--February--March.
This paper investigates the variability of the break-up dates of the rivers in Northeast China from their icebound states for the period of 1957--2005 and explores some potential explanatory mechanisms. Results show that the break-up of the two major rivers (the Heilongjiang River and Songhuajiang River) was about four days earlier, and their freeze-up was about 4--7 days delayed, during 1989--2005 as compared to 1971--1987. This interdecadal variation is evidently associated with the warming trend over the past 50 years. In addition, the break-up and freeze-up dates have large interannual variability, with a standard deviation of about 10--15 days. The break-up date is primarily determined by the January--February--March mean surface air temperature over the Siberian-Northeast China region via changes in the melting rate, ice thickness, and snow cover over the ice cover. The interannual variability of the break-up date is also significantly connected with the Northern Annular Mode (NAM), with a correlation coefficient of 0.35--0.55 based on the data from four stations along the two rivers. This relationship is attributed to the fact that the NAM can modulate the East Asian winter monsoon circulation and Siberian-Northeast China surface air temperature in January--February--March.
2009, 26(4): 707-716.
doi: 10.1007/s00376-009-8196-2
Abstract:
Connections between the spring Antarctic Oscillation (AAO) and the East Asian summer monsoon (EASM) in two reanalysis datasets---NCEP-1 (NCEP/NCAR Reanalysis 1) and ERA-40 (ECMWF 40-year Reanalysis)---are investigated in this study. Both show significant correlation between AAO and EASM rainfall over the Yangtze River valley, especially after about 1985. Though ERA-40 shows weaker anomalous signals connecting AAO and EASM over southern high latitudes than NCEP-1, both datasets reveal similar connecting patterns between them. A wave-train-like pattern appears in the upper levels, from southern high latitudes through east of Australia and from the Maritime Continent to East Asia. In positive AAO years, the cross equatorial southeasterly flow over the Maritime Continent in the lower levels is strengthened, the specific humidity of the whole atmosphere over East Asia increases, and convective activity is enhanced; thus the summer rainfall over East Asia increases. The spring AAO-EASM connection may be better represented in ERA-40.
Connections between the spring Antarctic Oscillation (AAO) and the East Asian summer monsoon (EASM) in two reanalysis datasets---NCEP-1 (NCEP/NCAR Reanalysis 1) and ERA-40 (ECMWF 40-year Reanalysis)---are investigated in this study. Both show significant correlation between AAO and EASM rainfall over the Yangtze River valley, especially after about 1985. Though ERA-40 shows weaker anomalous signals connecting AAO and EASM over southern high latitudes than NCEP-1, both datasets reveal similar connecting patterns between them. A wave-train-like pattern appears in the upper levels, from southern high latitudes through east of Australia and from the Maritime Continent to East Asia. In positive AAO years, the cross equatorial southeasterly flow over the Maritime Continent in the lower levels is strengthened, the specific humidity of the whole atmosphere over East Asia increases, and convective activity is enhanced; thus the summer rainfall over East Asia increases. The spring AAO-EASM connection may be better represented in ERA-40.
2009, 26(4): 717-726.
doi: 10.1007/s00376-009-8210-8
Abstract:
Recent observational study has shown that the southern center of the summer North Atlantic Oscillation (SNAO) was located farther eastward after the late 1970s compared to before. In this study, the cause for this phenomenon is explored. The result shows that the eastward shift of the SNAO southern center after the late 1970s is related to the variability of the Mediterranean-Black Sea (MBS) SST. A warm MBS SST can heat and moisten its overlying atmosphere, consequently producing a negative sea level pressure (SLP) departure over the MBS region. Because the MBS SST is negatively correlated with the SNAO, the negative SLP departure can enhance the eastern part of the negative-phase of the SNAO southern center, consequently producing an eastward SNAO southern center shift. Similarly, a cold MBS SST produces an eastward positive-phase SNAO southern center shift. The reason for why the MBS SST has an impact on the SNAO after the late 1970s but why it is not the case beforehand is also discussed. It is found that this instable relationship is likely to be attributed to the change of the variability of the MBS SST on the decadal time-scale. In 1951--1975, the variability of the MBS SST is quite weak, but in 1978--2002, it becomes more active. The active SST can enhance the interaction between the sea and its overlying atmosphere, thus strengthening the connection between the MBS SST and the SNAO after the late 1970s. The above observational analysis results are further confirmed by sensitivity experiments.
Recent observational study has shown that the southern center of the summer North Atlantic Oscillation (SNAO) was located farther eastward after the late 1970s compared to before. In this study, the cause for this phenomenon is explored. The result shows that the eastward shift of the SNAO southern center after the late 1970s is related to the variability of the Mediterranean-Black Sea (MBS) SST. A warm MBS SST can heat and moisten its overlying atmosphere, consequently producing a negative sea level pressure (SLP) departure over the MBS region. Because the MBS SST is negatively correlated with the SNAO, the negative SLP departure can enhance the eastern part of the negative-phase of the SNAO southern center, consequently producing an eastward SNAO southern center shift. Similarly, a cold MBS SST produces an eastward positive-phase SNAO southern center shift. The reason for why the MBS SST has an impact on the SNAO after the late 1970s but why it is not the case beforehand is also discussed. It is found that this instable relationship is likely to be attributed to the change of the variability of the MBS SST on the decadal time-scale. In 1951--1975, the variability of the MBS SST is quite weak, but in 1978--2002, it becomes more active. The active SST can enhance the interaction between the sea and its overlying atmosphere, thus strengthening the connection between the MBS SST and the SNAO after the late 1970s. The above observational analysis results are further confirmed by sensitivity experiments.
2009, 26(4): 727-735.
doi: 10.1007/s00376-009-9014-6
Abstract:
By examining the second leading mode (EOF2) of the summer rainfall in China during 1958--2001 and associated circulations, the authors found that this prominent mode was a dipole pattern with rainfall decreasing to the north of the Yangtze River and increasing to the south. This reverse relationship of the rainfalls to the north and to the south of the Yangtze River was related with the meridional circulations within East Asia and the neighboring region, excited by SST in the South China Sea-northwestern Pacific. When the SST was warmer, the geopotential heights at 500 hPa were positive in the low and high latitudes and negative in the middle latitudes. The anticyclone in the low latitudes favored the subtropical high over the northwestern Pacific (SHNP) shifting southwestward, leading to additional moisture transport over southern China. The anomalous atmospheric circulations along the East Asian coast tends to enhance upward movement over the region. Subsequently, rainfall in southern China is enhanced.
By examining the second leading mode (EOF2) of the summer rainfall in China during 1958--2001 and associated circulations, the authors found that this prominent mode was a dipole pattern with rainfall decreasing to the north of the Yangtze River and increasing to the south. This reverse relationship of the rainfalls to the north and to the south of the Yangtze River was related with the meridional circulations within East Asia and the neighboring region, excited by SST in the South China Sea-northwestern Pacific. When the SST was warmer, the geopotential heights at 500 hPa were positive in the low and high latitudes and negative in the middle latitudes. The anticyclone in the low latitudes favored the subtropical high over the northwestern Pacific (SHNP) shifting southwestward, leading to additional moisture transport over southern China. The anomalous atmospheric circulations along the East Asian coast tends to enhance upward movement over the region. Subsequently, rainfall in southern China is enhanced.
2009, 26(4): 736-747.
doi: 10.1007/s00376-009-9038-y
Abstract:
This paper reviews some aspects of evaluation of climate simulation, including the ITCZ, the surface air temperature (SAT), and the monsoon. A brief introduction of some recently proposed approaches in weather forecast verification is followed by a discussion on their possible application to evaluation of climate simulation. The authors suggest five strategies to extend the forecast verification methods to climate simulation evaluation regardless significant differences between the forecasts and climate simulations. It is argued that resolution, convection scheme, stratocumulus cloud cover, among other processes in the atmospheric general circulation model (AGCM) and the ocean-atmosphere feedback are the potential causes for the double ITCZ problem in coupled models and AGCM simulations, based on the system- and component-level evaluations as well as the downscaling strategies in some recent research. Evaluations of simulated SAT and monsoons suggest that both coupled models and AGCMs show good performance in representing the SAT evolution and its variability over the past century in terms of correlation and wavelet analysis but poor at reproducing rainfall, and in addition, the AGCM alone is not suitable for monsoon regions due to the lack of air-sea interactions.
This paper reviews some aspects of evaluation of climate simulation, including the ITCZ, the surface air temperature (SAT), and the monsoon. A brief introduction of some recently proposed approaches in weather forecast verification is followed by a discussion on their possible application to evaluation of climate simulation. The authors suggest five strategies to extend the forecast verification methods to climate simulation evaluation regardless significant differences between the forecasts and climate simulations. It is argued that resolution, convection scheme, stratocumulus cloud cover, among other processes in the atmospheric general circulation model (AGCM) and the ocean-atmosphere feedback are the potential causes for the double ITCZ problem in coupled models and AGCM simulations, based on the system- and component-level evaluations as well as the downscaling strategies in some recent research. Evaluations of simulated SAT and monsoons suggest that both coupled models and AGCMs show good performance in representing the SAT evolution and its variability over the past century in terms of correlation and wavelet analysis but poor at reproducing rainfall, and in addition, the AGCM alone is not suitable for monsoon regions due to the lack of air-sea interactions.
2009, 26(4): 748-762.
doi: 10.1007/s00376-009-9032-4
Abstract:
A unified chemistry-aerosol-climate model is applied in this work to compare climate responses to changing concentrat, ions of long-lived greenhouse gases (GHGs, CO2, CH4, N2O, tropospheric O3, and aerosols during the years 1951--2000. Concentrations of sulfate, nitrate, primary organic carbon (POA), secondary organic carbon (SOA), black carbon (BC) aerosols, and tropospheric O3 for the years 1950 and 2000 are obtained a priori by coupled chemistry-aerosol-GCM simulations, and then monthly concentrations are interpolated linearly between 1951 and 2000. The annual concentrations of GHGs are taken from the IPCC Third Assessment Report. BC aerosol is internally mixed with other aerosols. Model results indicate that the simulated climate change over 1951--2000 is sensitive to anthropogenic changes in atmospheric components. The predicted year 2000 global mean surface air temperature can differ by 0.8o with different forcings. Relative to the climate simulation without changes in GHGs, O3, and aerosols, anthropogenic forcings of SO2-4, BC, BC+SO2-4, BC+SO2-4+POA, BC+SO2-4+POA+SOA+NO-3, O3, and GHGs are predicted to change the surface air temperature averaged over 1971--2000 in eastern China, respectively, by -0.40oC, +0.62oC, +0.18oC, +0.15oC, -0.78oC, +0.43oC, and +0.85oC, and to change the precipitation, respectively, by -0.21, +0.07, -0.03, +0.02, -0.24, -0.08, and +0.10 mm d-1. The authors conclude that all major aerosols are as important as GHGs in influencing climate change in eastern China, and tropospheric O3 also needs to be included in studies of regional climate change in China.
A unified chemistry-aerosol-climate model is applied in this work to compare climate responses to changing concentrat, ions of long-lived greenhouse gases (GHGs, CO2, CH4, N2O, tropospheric O3, and aerosols during the years 1951--2000. Concentrations of sulfate, nitrate, primary organic carbon (POA), secondary organic carbon (SOA), black carbon (BC) aerosols, and tropospheric O3 for the years 1950 and 2000 are obtained a priori by coupled chemistry-aerosol-GCM simulations, and then monthly concentrations are interpolated linearly between 1951 and 2000. The annual concentrations of GHGs are taken from the IPCC Third Assessment Report. BC aerosol is internally mixed with other aerosols. Model results indicate that the simulated climate change over 1951--2000 is sensitive to anthropogenic changes in atmospheric components. The predicted year 2000 global mean surface air temperature can differ by 0.8o with different forcings. Relative to the climate simulation without changes in GHGs, O3, and aerosols, anthropogenic forcings of SO2-4, BC, BC+SO2-4, BC+SO2-4+POA, BC+SO2-4+POA+SOA+NO-3, O3, and GHGs are predicted to change the surface air temperature averaged over 1971--2000 in eastern China, respectively, by -0.40oC, +0.62oC, +0.18oC, +0.15oC, -0.78oC, +0.43oC, and +0.85oC, and to change the precipitation, respectively, by -0.21, +0.07, -0.03, +0.02, -0.24, -0.08, and +0.10 mm d-1. The authors conclude that all major aerosols are as important as GHGs in influencing climate change in eastern China, and tropospheric O3 also needs to be included in studies of regional climate change in China.
2009, 26(4): 763-772.
doi: 10.1007/s00376-009-9029-z
Abstract:
This paper describes the construction of a 0.5ox0.5o daily temperature dataset for the period of 1961--2005 over mainland China for the purpose of climate model validation. The dataset is based on the interpolation from 751 observing stations in China and comprises 3 variables: daily mean, minimum, and maximum temperature. The ``anomaly approach" is applied in the interpolation. The gridded climatology of 1971--2000 is first calculated and then a gridded daily anomaly for 1961--2005 is added to the climatology to obtain the final dataset. Comparison of the dataset with CRU (Climatic Research Unit) observations at the monthly scale shows general agreement between the two datasets. The differences found can be largely attributed to the introduction of observations at new stations. The dataset shows similar interannual variability as does CRU data over North China and eastern part of the Tibetan Plateau, but with a slightly larger linear trend. The dataset is employed to validate the simulation of three extreme indices based on daily mean, minimum, and maximum temperature by a high-resolution regional climate model. Results show that the model reproduces these indices well. The data are available at the National Climate Center of China Meteorological Administration, and a coarser resolution (1ox1o) version can be accessed via the World Wide Web.
This paper describes the construction of a 0.5ox0.5o daily temperature dataset for the period of 1961--2005 over mainland China for the purpose of climate model validation. The dataset is based on the interpolation from 751 observing stations in China and comprises 3 variables: daily mean, minimum, and maximum temperature. The ``anomaly approach" is applied in the interpolation. The gridded climatology of 1971--2000 is first calculated and then a gridded daily anomaly for 1961--2005 is added to the climatology to obtain the final dataset. Comparison of the dataset with CRU (Climatic Research Unit) observations at the monthly scale shows general agreement between the two datasets. The differences found can be largely attributed to the introduction of observations at new stations. The dataset shows similar interannual variability as does CRU data over North China and eastern part of the Tibetan Plateau, but with a slightly larger linear trend. The dataset is employed to validate the simulation of three extreme indices based on daily mean, minimum, and maximum temperature by a high-resolution regional climate model. Results show that the model reproduces these indices well. The data are available at the National Climate Center of China Meteorological Administration, and a coarser resolution (1ox1o) version can be accessed via the World Wide Web.
2009, 26(4): 773-782.
doi: 10.1007/s00376-009-8211-7
Abstract:
Projected changes in summer precipitation characteristics in China during the 21st century are assessed using the monthly precipitation outputs of the ensemble of three “best” models under the Special Report on Emissions Scenarios (SRES) A1B, A2, and B1 scenarios. The excellent reproducibility of the models both in spatial and temporal patterns for the precipitation in China makes the projected summer precipitation change more believable for the future 100 years. All the three scenarios experiments indicate a consistent enhancement of summer precipitation in China in the 21st century. However, the projected summer precipitation in China demonstrates large variability between sub-regions. The projected increase in precipitation in South China is significant and persistent, as well as in North China. Meanwhile, in the early period of the 21st century, the region of Northeast China is projected to be much drier than the present. But, this situation changes and the precipitation intensifies later, with a precipitation anomaly increase of 12.4%–20.4% at the end of the 21st century. The region of the Xinjiang Province probably undergoes a drying trend in the future 100 years, and is projected to decrease by 1.7%–3.6% at the end of the 21st century. There is no significant long-term change of the projected summer precipitation in the lower reaches of the Yangtze River valley. A high level of agreement of the ensemble of the regional precipitation change in some parts of China is found across scenarios but smaller changes are projected for the B1 scenario and slightly larger changes for the A2 scenario.
Projected changes in summer precipitation characteristics in China during the 21st century are assessed using the monthly precipitation outputs of the ensemble of three “best” models under the Special Report on Emissions Scenarios (SRES) A1B, A2, and B1 scenarios. The excellent reproducibility of the models both in spatial and temporal patterns for the precipitation in China makes the projected summer precipitation change more believable for the future 100 years. All the three scenarios experiments indicate a consistent enhancement of summer precipitation in China in the 21st century. However, the projected summer precipitation in China demonstrates large variability between sub-regions. The projected increase in precipitation in South China is significant and persistent, as well as in North China. Meanwhile, in the early period of the 21st century, the region of Northeast China is projected to be much drier than the present. But, this situation changes and the precipitation intensifies later, with a precipitation anomaly increase of 12.4%–20.4% at the end of the 21st century. The region of the Xinjiang Province probably undergoes a drying trend in the future 100 years, and is projected to decrease by 1.7%–3.6% at the end of the 21st century. There is no significant long-term change of the projected summer precipitation in the lower reaches of the Yangtze River valley. A high level of agreement of the ensemble of the regional precipitation change in some parts of China is found across scenarios but smaller changes are projected for the B1 scenario and slightly larger changes for the A2 scenario.
2009, 26(4): 783-792.
doi: 10.1007/s00376-009-9034-2
Abstract:
The regional climate change index (RCCI) is employed to investigate hot-spots under 21st century global warming over East Asia. The RCCI is calculated on a 1-degree resolution grid from the ensemble of CMIP3 simulations for the B1, A1B, and A2 IPCC emission scenarios. The RCCI over East Asia exhibits marked sub-regional variability. Five sub-regional hot-spots are identified over the area of investigation: three in the northern regions (Northeast China, Mongolia, and Northwest China), one in eastern China, and one over the Tibetan Plateau. Contributions from different factors to the RCCI are discussed for the sub-regions. Analysis of the temporal evolution of the hot-spots throughout the 21st century shows different speeds of response time to global warming for the different sub-regions. Hot-spots firstly emerge in Northwest China and Mongolia. The Northeast China hot-spot becomes evident by the mid of the 21st century and it is the most prominent by the end of the century. While hot-spots are generally evident in all the 5 sub-regions for the A1B and A2 scenarios, only the Tibetan Plateau and Northwest China hot-spots emerge in the B1 scenario, which has the lowest greenhouse gas (GHG) concentrations. Our analysis indicates that sub-regional hot-spots show a rather complex spatial and temporal dependency on the GHG concentration and on the different factors contributing to the RCCI.
The regional climate change index (RCCI) is employed to investigate hot-spots under 21st century global warming over East Asia. The RCCI is calculated on a 1-degree resolution grid from the ensemble of CMIP3 simulations for the B1, A1B, and A2 IPCC emission scenarios. The RCCI over East Asia exhibits marked sub-regional variability. Five sub-regional hot-spots are identified over the area of investigation: three in the northern regions (Northeast China, Mongolia, and Northwest China), one in eastern China, and one over the Tibetan Plateau. Contributions from different factors to the RCCI are discussed for the sub-regions. Analysis of the temporal evolution of the hot-spots throughout the 21st century shows different speeds of response time to global warming for the different sub-regions. Hot-spots firstly emerge in Northwest China and Mongolia. The Northeast China hot-spot becomes evident by the mid of the 21st century and it is the most prominent by the end of the century. While hot-spots are generally evident in all the 5 sub-regions for the A1B and A2 scenarios, only the Tibetan Plateau and Northwest China hot-spots emerge in the B1 scenario, which has the lowest greenhouse gas (GHG) concentrations. Our analysis indicates that sub-regional hot-spots show a rather complex spatial and temporal dependency on the GHG concentration and on the different factors contributing to the RCCI.
2009, 26(4): 793-802.
doi: 10.1007/s00376-009-9031-5
Abstract:
The recent progresses on the reconstruction of historical land cover and the studies on regional climatic effects to temperature, precipitation, and the East Asian Monsoon across China were reviewed. Findings show that the land cover in China has been significantly modified by human activities over the last several thousands years, mainly through cropland expansion and forest clearance. The cropland over traditional Chinese agricultural areas increased from 5.32x105 km2 in the mid-17th century to 8.27x105 km2 in the mid-20th century, while the forest area over the Chinese mainland had been reduced by 1.66x106 km2 during the last 300 years. These changes of land cover have been detected as an important driving force of climate change by simulations of climatic effects based on various climate models (including RegCM3, RegCM2-NCC, RIEMS version1, MM5 version 2, and AGCM+SSiB) with reconstructed historical land cover data or by contrasting current land cover to potential natural vegetation. The human-induced land cover changes over China have led to the enhancement of the East Asian winter monsoon, as well as cooling in winter and warming in summer approximately since 1700. However, the simulation results on annual mean temperature, precipitation, and the East Asian summer monsoon varied from model to model, which cannot be simply attributed to certain forcing so far, but undoubtedly, using different land cover datasets in various simulations played a key role. Thus, developing more accurate gridded historical land cover datasets on different regional scales with high time resolution is needed in the future.
The recent progresses on the reconstruction of historical land cover and the studies on regional climatic effects to temperature, precipitation, and the East Asian Monsoon across China were reviewed. Findings show that the land cover in China has been significantly modified by human activities over the last several thousands years, mainly through cropland expansion and forest clearance. The cropland over traditional Chinese agricultural areas increased from 5.32x105 km2 in the mid-17th century to 8.27x105 km2 in the mid-20th century, while the forest area over the Chinese mainland had been reduced by 1.66x106 km2 during the last 300 years. These changes of land cover have been detected as an important driving force of climate change by simulations of climatic effects based on various climate models (including RegCM3, RegCM2-NCC, RIEMS version1, MM5 version 2, and AGCM+SSiB) with reconstructed historical land cover data or by contrasting current land cover to potential natural vegetation. The human-induced land cover changes over China have led to the enhancement of the East Asian winter monsoon, as well as cooling in winter and warming in summer approximately since 1700. However, the simulation results on annual mean temperature, precipitation, and the East Asian summer monsoon varied from model to model, which cannot be simply attributed to certain forcing so far, but undoubtedly, using different land cover datasets in various simulations played a key role. Thus, developing more accurate gridded historical land cover datasets on different regional scales with high time resolution is needed in the future.
2009, 26(4): 803-812.
doi: 10.1007/s00376-009-9018-2
Abstract:
Using the monthly NCEP-NCAR reanalysis dataset, the monthly temperature and precipitation at surface stations of China, and the MM5 model, we examine impacts of vegetation cover changes in western China on the interdecadal variability of the summer climate over northwestern China during the past 30 years. It is found that the summer atmospheric circulation, surface air temperature, and rainfall in the 1990s were different from those in the 1970s over northwestern China, with generally more rainfall and higher temperatures in the 1990s. Associated with these changes, an anomalous wave train appears in the lower troposphere at the midlatitudes of East Asia and the low-pressure system to the north of the Tibetan Plateau is weaker. Meanwhile, the South Asian high in the upper troposphere is also located more eastward. Numerical experiments show that change of vegetation cover in western China generally forces anomalous circulations and temperatures and rainfall over these regions. This consistency between the observations and simulations implies that the interdecadal variability of the summer climate over northwestern China between the 1990s and 1970s may result from a change of vegetation cover over western China.
Using the monthly NCEP-NCAR reanalysis dataset, the monthly temperature and precipitation at surface stations of China, and the MM5 model, we examine impacts of vegetation cover changes in western China on the interdecadal variability of the summer climate over northwestern China during the past 30 years. It is found that the summer atmospheric circulation, surface air temperature, and rainfall in the 1990s were different from those in the 1970s over northwestern China, with generally more rainfall and higher temperatures in the 1990s. Associated with these changes, an anomalous wave train appears in the lower troposphere at the midlatitudes of East Asia and the low-pressure system to the north of the Tibetan Plateau is weaker. Meanwhile, the South Asian high in the upper troposphere is also located more eastward. Numerical experiments show that change of vegetation cover in western China generally forces anomalous circulations and temperatures and rainfall over these regions. This consistency between the observations and simulations implies that the interdecadal variability of the summer climate over northwestern China between the 1990s and 1970s may result from a change of vegetation cover over western China.
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