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2010 Vol. 27, No. 1

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2010, 27(1): 1-13. doi: 10.1007/s00376-009-8207-3
[Abstract](1069) [PDF 1834KB](1190)
Abstract:
After the passage of a cold front, spring in northern China, the outbreak of strong wind is often accompanied by dust emissions. Through analyses of data in the atmospheric boundary layer during a typical case, it is revealed there are rather regular gust wave packets superimposed on the basic strong wind flow. The gust-wind wave packets have a period equal to around 3--6 mins and possess coherent structure. As the vertical transport of momentum is decomposed into separate parts by (a) basic flow, (b) gust-wind, and (c) turbulence, they are all in a downwards direction at the lower levels of the atmospheric boundary layer during strong wind periods. However, (a) is the largest, while (b) and (c) are comparable. All these are very different from the case of normal weather. Besides, the friction velocity at the ground surface is also much larger than that of normal weather and should be corrected by taking the contributions of the basic flow and gust-wind into account.The strong basic flow with descending motion is very favorable for soil erosion and sand/dust emissions, but suppresses the entrainment of dust particles by keeping them within the bottom levels of the atmospheric boundary layer. Owing to the coherent structure of gust-wind, dust particles can effectively overcome the systematic descending air motion and penetrate into the middle and upper levels of the atmospheric boundary layer, and then propagate further and diffuse into the troposphere where ascending air motion prevails.
2010, 27(1): 14-32. doi: 10.1007/s00376-009-8206-4
Abstract:
In this paper, the influence of Typhoon Chanthu on Thailand during June 2004 was studied. Several major features have been revealed. (1) Chanthu formed and developed in favorable large-scale conditions. A continental high-pressure system covered most of China and merged with the West Pacific Subtropical High to become a west-east oriented high-pressure band, which was responsible for the westward movement of the typhoon. (2) There existed a stationary and active ITCZ, which was the preferred formation area of the typhoon. The ITCZ extended from the Bay of Bengal, through the Indo-China Peninsula and the South China Sea, to the western Pacific. Chanthu formed in the ITCZ and moved almost directly along it. (3) The moisture sources differed during the various stages of development. In the earlier stages, water vapor came largely from the South China Sea but in later stages, the source was mainly from the Bay of Bengal. The rich water vapor supply explains the long-lived effects of Chanthu and its remnants after landfall. (4) Cyclonic circulation remained following the landfall of Chanthu, as did a weak warm core in the upper-middle troposphere, which was likely caused by the release of latent heat from convective condensation. Due to the ample moisture supply from the ITCZ, convective activity was still very active after landfall. (5) Subgrid-scale convective systems played an important role in the kinetic energy budget. In addition, numerical simulations show that, among various cumulus convective parameterization schemes, the Betts-Miller-Janjic scheme seemed to be the best in the summer season.
2010, 27(1): 33-46. doi: 10.1007/s00376-009-8139-y
[Abstract](1078) [PDF 1407KB](1210)
Abstract:
The responses of vertical structures, in convective and stratiform regions, to the large-scale forcing during the landfall of tropical storm Bilis (2006) are investigated using the data from a two-dimensional cloud-resolving model simulation. An imposed large-scale forcing with upward motion in the mid and upper troposphere and downward motion in the lower troposphere on 15 July suppresses convective clouds, which leads to ～100% coverage of raining stratiform clouds over the entire model domain. The imposed forcing extends upward motion to the lower troposphere during 16--17 July, which leads to an enhancement of convective clouds and suppression of raining stratiform clouds. The switch of large-scale lower-tropospheric vertical velocity from weak downward motion on 15 July to moderate upward motion during 16--17 July produces a much broader distribution of the vertical velocity, water vapor and hydrometeor fluxes, perturbation specific humidity, and total hydrometeor mixing ratio during 16--17 July than those on 15 July in the analysis of contoured frequency-altitude diagrams. Further analysis of the water vapor budget reveals that local atmospheric moistening is mainly caused by the enhancement of evaporation of rain associated with downward motion on 15 July, whereas local atmospheric drying is mainly determined by the advective drying associated with downward motion over raining stratiform regions and by the net condensation associated with upward motion over convective regions during 16--17 July.
2010, 27(1): 47-59. doi: 10.1007/s00376-009-8014-x
[Abstract](1046) [PDF 766KB](946)
Abstract:
In this study, seasonal predictions were applied to precipitation in China on a monthly basis based on a multivariate linear regression with an adaptive choice of predictors drawn from regularly updated climate indices with a two to twelve month lead time. A leave-one-out cross validation was applied to obtain hindcast skill at a 1% significance level. The skill of forecast models at a monthly scale and their significance levels were evaluated using Anomaly Correlation Coefficients (ACC) and Coefficients Of Determination (COD). The monthly ACC skill ranged between 0.43 and 0.50 in Central China, 0.41--0.57 in East China, and 0.41--0.60 in South China. The dynamic link between large-scale climate indices with lead time and the precipitation in China is also discussed based on Singular Value Decomposition Analysis (SVDA) and Correlation Analysis (CA).
2010, 27(1): 60-68. doi: 10.1007/s00376-009-8050-6
Abstract:
Both box and inverse methods are used to study the relative importance of outflow passages of the South China Sea. The physical meaning of the box model is described in detail, and its optimization is based on the most efficient way to remove the warm and fresh water in terms of the heat and salt budgets. The box model results suggest that the Kalimantan Strait is the main outflow passage, because the water near the Kalimantan is the warmest and freshest. The system of the South China Sea advects the warmest and freshest water through the wide Kalimantan Strait out of the South China Sea to achieve a quick heat and salt balance because of the huge amount of heat flux and large precipitation gained from the atmosphere. These results are confirmed by an inverse method, in which detailed dynamics and thermohaline structure are considered. The velocity distribution in the transect of the Luzon Strait revealed by the inverse method is similar to that obtained by earlier studies.
2010, 27(1): 69-79. doi: 10.1007/s00376-009-7209-5
[Abstract](1076) [PDF 562KB](1077)
Abstract:
Based on gradient wind equations, including frictional force, and considering the effect of the movement of a tropical cyclone on wind speed, the Fujita Formula is improved and further simplified, and the numerical scheme for calculating the maximum wind speed radius and wind velocity distribution of a moving tropical cyclone is derived. In addition, the effect of frictional force on the internal structure of the tropical cyclone is discussed. By comparison with observational data, this numerical scheme demonstrates great advantages, i.e.: it can not only describe the asymmetrical wind speed distribution of a tropical cyclone reasonably, but can also calculate the maximum wind speed in each direction within the typhoon domain much more accurately. Furthermore, the combination of calculated and analyzed wind speed distributions by the scheme is perfectly consistent with observations.
2010, 27(1): 80-86. doi: 10.1007/s00376-009-8151-2
Abstract:
Surface albedo over typical types of surfaces in the North China Plain was observed using a Multi-field Albedo Observation System before and after several snowfalls from 13 to 27 February 2005. Dramatic variations of the surface albedos of bare land, a frozen pond, and withered grassland during that period were analyzed. Under cloudy sky, the mean surface albedo of bare land was about 0.23, but it immediately rose to 0.85 when the surface was covered by fresh snow. The albedo decreased gradually to normal levels afterwards. The melting processes were different depending on the characteristics of the underlying surfaces. For example, over grassland the surface albedo was relatively lower after snowfall, and as a result, more solar energy could be absorbed and consequently the snow melting process was accelerated. Significant variations of surface albedo cannot be easily captured by satellite observations; therefore, detailed measurements of surface albedo and related parameters are essential for determining the impact of snow on the energy budget of the Earth.
2010, 27(1): 87-94. doi: 10.1007/s00376-009-8061-3
[Abstract](964) [PDF 945KB](1198)
Abstract:
Changes in the Indonesian Throughflow (ITF) and the South China Sea throughflow---measured by the Luzon Strait Transport (LST)---associated with the 1976/77 regime shift are analyzed using the Island Rule theory and the Simple Ocean Data Assimilation dataset. Results show that LST increased but ITF transport decreased after 1975. Such changes were induced by variations in wind stress associated with the regime shift. The strengthening of the easterly wind anomaly east of the Luzon Strait played an important role in the increase of LST after 1975, while the westerly wind anomaly in the equatorial Pacific contributed significantly to the decrease in ITF transport after 1975, accounting for 53% of the change. After 1975, the Kuroshio Current strengthened and the Mindanao Current weakened in response to a decrease in the total transport of the North Equatorial Current. Both the North Equatorial Countercurrent and the South Equatorial Current weakened after 1975, and an anomalous cyclonic circulation in the western equatorial Pacific prevented the tropical Pacific water from entering the Indian Ocean directly.
2010, 27(1): 95-99. doi: 10.1007/s00376-009-8067-x
[Abstract](1040) [PDF 545KB](977)
Abstract:
Mechanisms for the spatio-temporal development of the Tropical Pacific Meridional Mode (TPMM) are investigated using a coupled ocean-atmosphere model and observations. In both observations and the model, this meridional mode displays decadal variations and is most pronounced in spring and early summer. The model simulation suggests that once SST anomalies in the subtropical northeastern Pacific are initiated, say by northeasterly trade wind variability, perturbations evolve into a merdional dipole in 2--3 months. A wind-evaporative-SST feedback causes a southwestward propagation of initial subtropical SST anomalies, while anomalous equatorial upwelling helps form the southern lobe of the meridional dipole. The TPMM development is a fast process (a few months) and depends on the seasonal cycle.
2010, 27(1): 100-114. doi: 10.1007/s00376-009-8178-4
[Abstract](961) [PDF 523KB](1039)
Abstract:
Abstract Methane (CH4) emissions from paddy rice fields substantially contribute to the dramatic increase of this greenhouse gas in the atmosphere. Due to great concern about climate change, it is necessary to predict the effects of the dramatic increase in atmospheric carbon dioxide (CO2) on CH4 emissions from paddy rice fields. CH4MOD 1.0 is the most widely validated model for simulating CH4 emissions from paddy rice fields exposed to ambient CO2 (hereinafter referred to as aCO2). We upgraded the model to CH4MOD 2.0 by: (a) modifying the description of the influences of soil Eh and the water regime on CH4 production; (b) adding new features to reflect the regulatory effects of atmospheric CO2 upon methanogenic substrates, soil Eh during drainages, and vascular CH4 transport; and (c) adding a new feature to simulate the influences of nitrogen (N) addition rates on methanogenic substrates under elevated CO2 (hereinafter referred to as eCO2) condition. Validation with 109 observation cases under aCO2 condition showed that CH4MOD 2.0 possessed a minor systematic bias in the prediction of seasonally accumulated methane emissions (SAM). Validation with observations in free-air CO2 enrichment (FACE) experiments in temperate and subtropical climates showed that CH4MOD 2.0 successfully simulated the effects of eCO2 upon SAM from paddy rice fields incorporated with various levels of previous crop residues and/or N fertilizer. Our results imply that CH4MOD 2.0 provides a potential approach for estimating of the effects of elevated atmospheric CO2 upon CH4 emissions from regional or global paddy rice fields with various management practices in a changing climate.
2010, 27(1): 115-122. doi: 10.1007/s00376-009-8193-5
Abstract:
The diurnal variability of precipitation depth over the Tibetan Plateau and its surrounding regions is investigated using nine years of Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) measurements. The Tibetan Plateau, the plains area, and the East China Sea are selected as the focus regions in this study. The average precipitation depths (PD) are about 4.6 km, 5.8 km, and 5.6 km, while convective (stratiform) PDs are about 6.6 (4.5) km, 7.5 (5.7) km, and 6.0 (5.6) km over the plateau, the plains, and the ocean region, respectively. Results demonstrate a prominent PD diurnal cycle, and its diurnal phase is generally a few hours behind the surface precipitation. The spatial variation of the PD diurnal magnitude is weaker near the coastal areas than that of surface precipitation. The height of the PD diurnal peak is around 6--7 km for convective systems and 5--6 km for stratifrom systems. The dominant afternoon diurnal peak for convective PD and the flat diurnal peak for stratiform PD over the Tibetan Plateau indicate that solar diurnal forcing is the key mechanism of the PD diurnal cycle over land. In addition, the diurnal variation is obvious for shallow and deep convective systems, but not for shallow and deep stratiform systems.
2010, 27(1): 123-136. doi: 10.1007/s00376-009-8154-z
[Abstract](1010) [PDF 1250KB](1587)
Abstract:
During the period between 18 August and 22 September 2006, an ultraviolet photometric O3 analyzer, a NO-NO2-NOx chemiluminescence analyzer, and a quartz micro-oscillating-scale particle concentration analyzer were simultaneously used for monitoring at three different heights each at Beijing (325-m tower) and Tianjin (255-m tower). These towers belong to the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences (CAS) and to the Tianjin Municipal Meteorological Bureau, respectively. These measurements were used to continuously measure the atmospheric O3 and NOx volume-by-volume concentrations and the PM2.5 mass concentration within a vertical gradient. When combined with meteorological data and information on the variation of vertical characteristics of the various atmospheric pollutants in the two cities, analysis shows that these two cities were seriously polluted by both PM2.5 and O3 during summer and autumn. The highest daily-average concentrations of PM2.5 near the ground in Beijing and Tianjin reached 183 μg m-3 and 165 μg m-3, respectively, while the O3 concentrations reached 52 ppb and 77 ppb, and NOx concentrations reached 48 ppb and 62 ppb for these two cities, respectively. The variations in the daily-average concentrations of PM2.5 between Beijing and Tianjin were demonstrated to be consistent over time. The concentrations of PM2.5 measured in Beijing were found to be higher than those in Tianjin. However, the overall O3 concentrations near the ground in Tianjin were higher than in Beijing. NOx concentrations in Tianjin were consistently lower than in Beijing. It was also found that PM2.5 pollution in Beijings atmosphere may also be affected by the pollutants originating in and delivered from Tianjin, and that Ti
2010, 27(1): 137-150. doi: 10.1007/s00376-009-8191-7
[Abstract](923) [PDF 720KB](1319)
Abstract:
In this study, in order to numerically simulate daily nitrous oxide (N2O) emission from a rice-winter wheat rotation cropping system, we developed a process-based site model (referred to as IAP-N-GAS) tracking the movement and transformation of several forms of nitrogen in the agroecosystem, which is affected by climate, soil, crop growth and management practices. The simulation of daily N2O fluxes, along with key daily environmental variables, was validated with three-year observations conducted in East China. The validation demonstrated that the model simulated daily solar radiation, soil temperature and moisture well, and it almost exactly captured the dynamics and magnitude of accumulated rice above-ground biomass and mineral nitrogen in the soil. The simulated daily N2O emissions over all three years investigated were generally in good agreement with field observations. In particular, the peak N2O emissions induced by fertilizations, rainfall events or mid-season drainages, were well simulated. The model simulation also closely represented the inter-annual variation in N2O emission. These validations imply that the model has the capability to capture the general characteristics of N2O emission from a typical rice-wheat rotation agroecosystem. Sensitivity analyses revealed that the simulated N2O emission is most sensitive to the fertilizer application rate and the soil organic matter content, but it is much less sensitive to variations in the soil pH and texture, temperature, precipitation and crop residue incorporation rate under local conditions.
2010, 27(1): 154-163. doi: 10.1007/s00376-009-8117-4
Abstract:
The combined approach', which is suitable to represent subgrid land surface heterogeneity in both inter-patch and intra-patch variabilities, is employed in the Biosphere/Atmosphere Transfer Scheme (BATS) as a land surface component of the regional climate model RegCM3 to consider the heterogeneities in temperature and moisture at the land surface, and then annual-scale simulations for 5 years (1988--1992) were conducted. Results showed that on the annual scale, the models response to the heterogeneities is quite sensitive, and that the effect of the temperature heterogeneity (TH) is more pronounced than the moisture heterogeneity (MH). On the intraannual scale, TH may lead to more (less) precipitation in warm (cold) seasons, and hence lead to larger intraannual variability in precipitation; the major MH effects may be lagged by about 1 month during the warm, rainy seasons, inducing ～6% more precipitation for some sub-regions. Additionally, the modeled climate for the northern sub-regions shows larger sensitivities to the land surface heterogeneities than those for the southern sub-regions. Since state-of-art land surface models seldom account for surface intra-patch variabilities, this study emphasizes the importance of including this kind of variability in the land surface models.
2010, 27(1): 164-176. doi: 10.1007/s00376-009-8146-z
[Abstract](1615) [PDF 392KB](968)
Abstract:
At present, the Topographic Index Model (TOPMODEL) has been recommended for integration in Land Surface Models (LSMs). But, the applicable scope of the original TOPMODEL (OTOP) is limited because the OTOP derivation relies on three fundamental but unrealistic assumptions. In this paper, several versions of a generalized TOPMODEL (GTOP), which relax some unrealistic assumptions involved in OTOP, are presented, and the theoretical derivationsn to obtain these modifications are demonstrated in detail. Specifically, the extension for the OTOP applicability comes down to following three basic cases: (1) Give up the assumption of spatially uniform recharge rate to the groundwater and let the rate be spatially varying, (2) Keep same original exponential distribution profile of hydraulic conductivity used in OTOP but change the saturated hydraulic conductivity and effective soil depth from spatial constants in OTOP to spatially variable quantities; and (3) Extend the original exponential distribution profile of hydraulic conductivity to more general power law distribution profile of hydraulic conductivity together with spatially variable saturated hydraulic conductivity and effective soil depth. Finally, a brief numerical sensitivity study based on one version of GTOP using an exponential distribution profile for soil hydraulic conductivity is conducted. This shows the heterogeneous effects of the effective soil depth, saturated hydraulic conductivity,at ground surface and groundwater recharge rate on hydrological processes and serves as an example application of GTOP to a heterogeneous catchment.
2010, 27(1): 177-184. doi: 10.1007/s00376-009-8144-1
Abstract:
The relationship between the boreal winter (December, January, February) Aleutian Low (AL) and the simultaneous Australian summer monsoon (ASM) is explored in this study. A significant correlation is found between the North Pacific index (NPI) and ASM index, the bulk of which is attributed to the significant correlation after late 1970s. Significant differences in precipitation and outgoing long-wave radiation between typical negative and positive NPI years appear over the ASM area. A regression analysis of the circulation pattern against the NPI during the three months is performed separately. We propose that the NPI is related with the ASM circulation possibly through the changes in the upper level westerly jet. In a typical negative NPI (strong Aleutian Low) year, the jet is greatly reinforced and the anomalous anticyclonic circulation to the south is thus excited, from which the easterly wind anomalies flowing into the ASM region emanate. Further, strong sinking motion over the northern entrance region of the jet is enhanced, and the local Hadley circulation anomaly between the ASM region and the coast of East Asia is strengthened. In this way, anomalous upward motion over the ASM area can thus be strengthened, and the convective activity intensified. Then the monsoon rainfall over ASM area is increased. An asymmetric' connection between AL and the monsoon is found in this study.
2010, 27(1): 185-194. doi: 10.1007/s00376-009-8089-4
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This paper outlines a methodology to estimate monthly precipitation surfaces at 1-km resolution for the Upper Shiyang River watershed (USRW) in northwest China. Generation of precipitation maps is based on the application of a four-variable genetic algorithm (GA) trained on 10 years of weather and ancillary data, i.e., surface air temperature, relative humidity, Digital Elevation Model-derived estimates of elevation, and time of year collected at 29 weather stations in west-central Gansu and northern Qinghai province. An observed-to-GA predicted data comparison of 10 years of precipitation collected at the 29 weather stations showed that about 84\% of the variability in observed values could be explained by the trained GA, including variability in two independent datasets. Point-comparisons of observed and modeled precipitation along an elevation-rainfall gradient demonstrated near-similar spatiotemporal patterns. A precipitation surface for USRW for July, 2005, was developed with the trained GA and input surfaces of surface air temperature and relative humidity generated from Moderate Resolution Imaging Spectroradiometer sensor (MODIS) products of land surface temperature. Spatial tendencies in predicted maximum and minimum values of surface air temperature, relative humidity, and precipitation within a 2-km radius circle around selected weather stations were in close agreement with the values measured at the weather stations.