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2009 Vol. 26, No. 2

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2009, 26(2): 191-191. doi: 10.1007/s00376-009-0191-0
[Abstract](1200) [PDF 23KB](902)
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2009, 26(2): 192-201. doi: 10.1007/s00376-009-0192-z
[Abstract](1181) [PDF 1856KB](2137)
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East Asia experienced a significant interdecadal climate shift around the late 1970s, with more floods in the valley of the Yangtze River of central-eastern China and more severe drought in North China since then. Whether global SST variations have played a role in this shift is unclear. In the present study, this issue is investigated by ensemble experiments of an atmospheric general circulation model (AGCM), the GFDL AM2, since one validation reveals that the model simulates the observed East Asian Summer Monsoon (EASM) well. The results suggest that decadal global SST variations may have played a substantial role in this climate shift. Further examination of the associated atmospheric circulation shows that these results are physically reasonable.
2009, 26(2): 202-210. doi: 10.1007/s00376-009-0202-1
[Abstract](1184) [PDF 1328KB](1269)
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Cluster analysis has been performed on the tracks of 51 Tropical Cyclones (TCs) that made landfall on the Korean Peninsula (KP) for the period of 1951--2004. The classification technique of the landfalling tracks used in this study was the fuzzy clustering method (FCM) and the resultant silhouette coefficient suggested four clusters as an optimal cluster number. Most TCs of Cluster 2 and Cluster 3 (C-23) tended to pass through mainland China before landfall, but those of Cluster 1 and Cluster 4 (C-14) tended to mostly land after moving northward from the East China Sea (ECS) without passing over mainland China. The TC landfalling frequency of C-14 has begun to clearly increase since the late 1980s, particularly the maximum landfalling frequency in the early 2000s set a record for the 54-year analysis period. The ridge axis of the western North Pacific high (WNPH) of C-23 bends more equatorward than that of C-14, so that the monsoon trough of C-23 is located more equatorward than that of C-14. As a consequence, most TCs of C-23 tend to recurve inland of China, but over the ECS for C-14.
2009, 26(2): 211-221. doi: 10.1007/s00376-009-0211-0
[Abstract](1216) [PDF 751KB](1509)
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Data from a long term measurement of Micro Rain Radar (MRR) at a mountain site (Daegwallyeong, DG, one year period of 2005) and a coastal site (Haenam, HN, three years 2004--2006) in South Korea were analyzed to compare the MRR measured bright band characteristics of stratiform precipitation at the two sites. On average, the bright band was somewhat thicker and the sharpness (average gradient of reflectivity above and below the reflectivity peak) was slightly weaker at DG, compared to those values at HN. The peak reflectivity itself was twice as strong and the relative location of the peak reflectivity within the bright band was higher at HN than at DG. Importantly, the variability of these values was much larger at HN than at DG. The key parameter to cause these differences is suggested to be the difference of the snow particle densities at the two sites, which is related to the degree of riming. Therefore, it is speculated that the cloud microphysical processes at HN may have varied significantly from un-rimed snow growth, producing low density snow particles, to the riming of higher density particles, while snow particle growth at DG was more consistently affected by the riming process, and therefore high density snow particles. Forced uplifting of cloudy air over the mountain area around DG might have resulted in an orographic supercooling effect that led to the enhanced riming of supercooled cloud drops.
2009, 26(2): 222-228. doi: 10.1007/s00376-009-0222-x
[Abstract](1090) [PDF 429KB](1105)
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The snow enhancement experiments, carried out by injecting AgI and water vapor into orographically enhanced clouds (fog), have been conducted to confirm Li and Pitter's forced condensation process in a natural situation. Nine ground-based experiments have been conducted at Daegwallyeong in the Taebaek Mountains for the easterly foggy days from January--February 2006. We then obtained the optimized conditions for the Daegwallyeong region as follows: the small seeding rate (1.04 g min-1) of AgI for the easterly cold fog with the high humidity of Gangneung. Additional experiments are needed to statistically estimate the snowfall increment caused by the small AgI seeding into the orographical fog (cloud) over the Taebaek Mountains.
2009, 26(2): 229-239. doi: 10.1007/s00376-009-0229-3
[Abstract](1054) [PDF 706KB](1326)
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In this study, using the ECMWF reanalysis data, the possible linkage between the Pacific-North American teleconnection pattern (PNA) and the North Atlantic Oscillation (NAO) during boreal winter (December--February) is investigated. The PNA and the NAO pattern are obtained by performing Rotated Empirical Orthogonal Function (REOF) analysis on an anomalous daily mean 300-hPa geopotential height field. The composite daily NAO indices show that the NAO indices are prone to be negative (positive) when the contemporary PNA indices are extremely positive (negative). The correlation coefficients between the daily PNA and NAO indices also confirm that, indeed, there is a significant anti-correlation between the PNA and NAO indices. The correlation peaks at a lag of 0 days (meaning contemporary correlation), and its value is 0.202. Analyses of a newly defined Rossby wave breaking index and diagnostics of the stream function tendency equation indicate that the anti-correlation between PNA and NAO may be caused by the anomalous Rossby wave breaking events associated with the PNA pattern.
2009, 26(2): 240-252. doi: 10.1007/s00376-009-0240-8
[Abstract](1160) [PDF 1003KB](1942)
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Rapid and significant advances in issues relevant to weather modification have been made in the last decade in China due to high water resource stresses and severe weather hazards induced by climate change. This paper reported some progress in aspects of theoretical modeling, field experiment and cloud-seeding tools, as well as research projects regarding weather modification during the ten years from 1997 to 2007. More advanced theoretical models such as cloud models with bin-microphysics and glaciogenic and hygroscopic seeding processes, and mesoscale cloud-resolving models with AgI-seeding processes have been developed to study seeding-induced changes of cloud structure and precipitation as well as to understand critical issues in association with weather modification. More advanced cloud-seeding tools such as mobile ground-based launching system of AgI-rockets and aircraft-based AgI-flares have been developed and used in operation. Several important projects aimed at exploring weather modification techniques and their applications have been conducted during this period.
2009, 26(2): 253-264. doi: 10.1007/s00376-009-0253-3
[Abstract](1126) [PDF 1211KB](1200)
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This paper examined the decadal mean, seasonal cycle, and interannual variations of mean and extreme temperatures using daily temperature and relative humidity data from 589 stations over eastern China and South Korea between 1996--2005. The results show that the decadal mean Tm (mean daily mean temperature) and the TNn (minimum daily minimum temperature) increase from north to south; the opposite spatial gradient is found in the DTR (diurnal temperature range); the value of the DTR over South Korea is in-between that over North China and the mid-low Yangtze River valley; the TXx (maximum daily maximum temperature) has a unique spatial distribution, with the largest value over eastern China. The highest standard deviation (STD) is located over northern China and the TNn has the largest area coverage of the high STD. The peak of the seasonal cycle for the Tm, TXx and TNn over South Korea (August) occurs one month later than that over eastern China (July). The seasonal cycle of the DTR has two peaks (April and October); the value in the middle-lower reaches of the Yangtze River valley is larger than that in South Korea during July and August owing to the seasonal northward jump of the major monsoon rain band. The interannual variations of summertime temperature indices including the T, TXx, and DTR over South Korea are consistent (opposite) to that over northern (southern) China. For the wintertime temperature indices however, the variation over South Korea is consistent with that over eastern China.
2009, 26(2): 265-274. doi: 10.1007/s00376-009-0265-z
[Abstract](1007) [PDF 843KB](1137)
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A global ocean general circulation model (L30T63) is employed to study the uptake and distribution of anthropogenic CO2 in the ocean. A subgrid-scale mixing scheme called GM90 is used in the model. There are two main GM90 parameters including isopycnal diffusivity and skew (thickness) diffusivity. Sensitivities of the ocean circulation and the redistribution of dissolved anthropogenic CO2 to these two parameters are examined. Two runs estimate the global oceanic anthropogenic CO2 uptake to be 1.64 and 1.73 Pg C yr-1 for the 1990s, and that the global ocean contained 86.8 and 92.7 Pg C of anthropogenic CO2 at the end of 1994, respectively. Both the total inventory and uptake from our model are smaller than the data-based estimates. In this presentation, the vertical distributions of anthropogenic CO2 at three meridional sections are discussed and compared with the available data-based estimates. The inventory in the individual basins is also calculated. Use of large isopycnal diffusivity can generally improve the simulated results, including the exchange flux, the vertical distribution patterns, inventory, storage, etc. In terms of comparison of the vertical distributions and column inventory, we find that the total inventory in the Pacific Ocean obtained from our model is in good agreement with the data-based estimate, but a large difference exists in the Atlantic Ocean, particularly in the South Atlantic. The main reasons are weak vertical mixing and that our model generates small exchange fluxes of anthropogenic CO2 in the Southern Ocean. Improvement in the simulation of the vertical transport and sea ice in the Southern Ocean is important in future work.
2009, 26(2): 275-282. doi: 10.1007/s00376-009-0275-x
[Abstract](1046) [PDF 338KB](1296)
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The regional distribution of perceived temperatures (PT) for 28 major weather stations in South Korea during the past 22 years (1983--2004) was investigated by employing a human heat budget model, the Klima-Michel model. The frequencies of a cold stress and a heat load by each region were compared. The sensitivity of PT in terms of the input of synoptic meteorological variables were successfully tested. Seogwipo in Jeju Island appears to be the most comfortable city in Korea. Busan also shows a high frequency in the comfortable PT range. The frequency of the thermal comfort in Seoul is similar to that of Daejeon with a relatively low frequency. In this study, inland cities like Daegu and Daejeon had very hot thermal sensations. Low frequencies of hot thermal sensations appeared in coastal cities (e.g., Busan, Incheon, and Seogwipo). Most of the 28 stations in Korea exhibited a comfort thermal sensation over 40% in its frequency, except for the mountainous regions. The frequency of a heat load is more frequent than that of a cold stress. There are no cities with very cold thermal sensations. In this study, we found the decreasing trend of mortality with an increasing PT. If the PT is over any critical temperature point, however, the mortality rate increases again. The mortality variation with the PT of a station seems to be associated with the latitudinal location of the station, implying that it results from a regional acclimation effect of inhabitants.
2009, 26(2): 283-292. doi: 10.1007/s00376-009-0283-x
[Abstract](1009) [PDF 886KB](1141)
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Spatiotemporal changes in air temperature and humidity associated with the restoration of an inner-city stream in Seoul, Korea, are investigated based on long-term monitoring data. The Cheonggye stream, covered under a concrete structure for 46 years, was restored in 2005 and runs 5.8 km eastward through a central region of Seoul. Long-term monitoring of the air temperature and relative humidity was made along the stream throughout the restoration and across the stream after the restoration. The area along the stream had a higher air temperature than the entire metropolitan area. The temperature anomaly between the monitoring area and the surrounding metropolitan area was 0.13oC lower on average at the center of the stream after the restoration. The stream's effect on the air temperature was also evident in the temperature distribution along a street traversing the stream. The relative and specific humidities were increased due to the restoration. The restored stream modified the nearby urban climate in the opposite direction compared to urbanization. The results could be used as a model case in mitigating urban climate by a stream in future urban planning practices.
2009, 26(2): 293-304. doi: 10.1007/s00376-009-0293-8
[Abstract](1091) [PDF 1489KB](1413)
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Based on a five-variable theoretical ecosystem model, the stability of equilibrium state and the nonlinear feature of the transition between a grassland state and a desert state are investigated. The approach of the conditional nonlinear optimal perturbations (CNOPs), which are the nonlinear generalization of the linear singular vectors (LSVs), is adopted. The numerical results indicate that the linearly stable grassland and desert states are nonlinearly unstable to large enough initial perturbations on the condition that the moisture index $\mu$ satisfies 0.3126<μ<0.3504. The perturbations represent some kind of anthropogenic influence and natural factors. The results obtained by CNOPs, LSVs and Lyapunov vectors (LVs) are compared to analyze the nonlinear feature of the transition between the grassland state and the desert state. Besides this, it is shown that the five-variable model is superior to the three-variable model in providing more visible signals when the transitions occur.
2009, 26(2): 305-311. doi: 10.1007/s00376-009-0305-8
[Abstract](1581) [PDF 516KB](1259)
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Based on TOMS total ozone data and SCIAMACHY ozone profile data, climatology of the ozone mini-hole events over the Tibetan Plateau and ozone vertical structure variations during an ozone mini-hole event in December 2003 are analyzed. The analyses show that before 1990 ozone mini-hole events only occurred in November--December of 1987 but that the number of events increases after 1990. These events only occur from October through February, with maximum occurrence frequency in December. During the event in December 2003, the decrease in total ozone of over 20\% is mainly caused by the ozone loss in the upper troposphere and lower stratosphere region due to the horizontal transport of low ozone from the lower latitude subtropics and the uplift of low ozone from the lower troposphere over the Tibetan Plateau.
2009, 26(2): 312-318. doi: 10.1007/s00376-009-0312-9
[Abstract](1132) [PDF 500KB](1492)
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Temporal-spatial variations in tropospheric ozone concentrations over East Asia in the period from 1 January 2000 to 31 December 2004 were simulated by using the Models-3 Community Multi-scale Air Quality (CMAQ) modeling system with meteorological fields calculated by the Regional Atmospheric Modeling System (RAMS). The simulated concentrations of ozone and carbon monoxide were compared with ground level observations at two remote sites, Ryori (39.03oN, 141.82oE) and Yonagunijima (24.47oN, 123.02oE). The comparison shows that the model reproduces their seasonal variation patterns reasonably well, and simulated ozone levels are generally in good agreement with the observed ones, but carbon monoxide concentrations are underestimated. Analysis of horizontal distributions of monthly averaged ozone mixing ratios in the surface layer indicates that ozone concentrations have noticeable differences among the four seasons; they are generally higher in the spring and summer while lower in the winter, reflecting the seasonal variation of solar intensity and photochemical activity and the fact that the monsoons over East Asia are playing an important role in ozone distributions.
2009, 26(2): 319-326. doi: 10.1007/s00376-009-0319-2
[Abstract](1138) [PDF 415KB](1495)
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The semi-arid regions, as climatic and ecosystem transitional zones, are the most vulnerable to global environmental change. Earlier researches indicate that the semi-arid regions are characterized by strong land-atmosphere coupling in which soil moisture is the crucial variable in land surface processes. In this paper, we investigate the sensitivity of the sensible/latent heat fluxes to soil moisture during the growing season based on the enhanced observations at Tongyu in the Jilin province of China, a reference site of international Coordinated Energy and Water Cycle Observations Project (CEOP) in the semi-arid regions, by using a sophisticated land surface model (NCAR_CLM3.0). Comparisons between the observed and simulated sensible/latent heat fluxes indicate that the soil moisture has obvious effects on the sensible/latent heat fluxes in terms of diurnal cycle and seasonal evolution. Better representation of the soil moisture could improve the model performance to a large degree. Therefore, for the purpose of simulating the land-atmosphere interaction and predicting the climate and water resource changes in semi-arid regions, it is necessary to enhance the description of the soil moisture distribution both in the way of observation and its treatment in land surface models.
2009, 26(2): 327-332. doi: 10.1007/s00376-009-0327-2
[Abstract](1135) [PDF 125KB](1072)
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The objective of this study is to improve the statistical modeling for the ternary forecast of heavy snowfall in the Honam area in Korea. The ternary forecast of heavy snowfall consists of one of three values, 0 for less than 50 mm, 1 for an advisory (50--150 mm), and 2 for a warning (more than 150 mm). For our study, the observed daily snow amounts and the numerical model outputs for 45 synoptic factors at 17 stations in the Honam area during 5 years (2001 to 2005) are used as observations and potential predictors respectively. For statistical modeling and validation, the data set is divided into training data and validation data by cluster analysis. A multi-grade logistic regression model and neural networks are separately applied to generate the probabilities of three categories based on the model output statistic (MOS) method. Two models are estimated by the training data and tested by the validation data. Based on the estimated probabilities, three thresholds are chosen to generate ternary forecasts. The results are summarized in 3×3 contingency tables and the results of the three-grade logistic regression model are compared to those of the neural networks model. According to the model training and model validation results, the estimated three-grade logistic regression model is recommended as a ternary forecast model for heavy snowfall in the Honam area.
2009, 26(2): 333-342. doi: 10.1007/s00376-009-0333-4
[Abstract](1262) [PDF 878KB](1764)
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ENSO's effect on the rainfall in eastern China in the following early summer is investigated by using station precipitation data and the ERA-40 reanalysis data from 1958 to 2002. In June, after the El Ni\~no peak, the precipitation is significantly enhanced in the Yangtze River valley while suppressed in the Huaihe River-Yellow River valleys. This relationship between ENSO and the rainfall in eastern China is established possibly through two teleconnections: One is related to the western North Pacific (WNP) anticyclonic anomaly in the lower troposphere leading to enhanced precipitation in the Yangtze River valley, and the other is related to the southward displacement of the Asian jet stream (AJS) in the upper troposphere resulting in suppressed precipitation in the Huaihe River-Yellow River valleys. This southward displacement of the AJS is one part of ENSO's effect on the zonal flow in the whole Northern Hemisphere. After the El Ni\~no peak, the ENSO-related warming in the tropical troposphere persists into the following early summer, increasing the meridional temperature gradient and through the thermal wind balance, leads to the enhancement of westerly flow in the subtropics south of the westerly jet stream and results in a southward displacement of the westerly jet stream.
2009, 26(2): 343-351. doi: 10.1007/s00376-009-0343-2
[Abstract](1137) [PDF 645KB](1396)
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Tropical zonally symmetric atmospheric warming occurs during ENSO's warm phase, and lags the equatorial east Pacific sea surface temperatures (SSTs) by 3--4 months. The role of the Indian and Atlantic oceans on the atmospheric delayed response has been pointed out by earlier studies. For 1951--2004, a regression analysis based on the observed SST data shows the western Pacific has a similarly important role as the Indian and Atlantic. Nevertheless, there is time mismatch of around 1--2 months between the zonally averaged tropical SST anomalies and the atmospheric temperature anomalies. It is expected that the tropospheric temperature should be controlled by diabatic heating forcing, which is sensitive primarily to SST anomalies over regions of high climatological SST, rather than to the tropical mean SST anomalies. To describe this mechanism, we propose a parameterization scheme of diabatic heating anomalies dependant on SST anomalies and climatological SST. The 1--2 month mismatch between tropical mean SST anomalies and air temperature anomalies is reconciled by the fact that the tropical mean heating anomalies are dominated by the SST anomalies over regions of high climatological SST, and lag the tropical mean SST anomalies by 1 month. The mechanism described by this parameterization scheme joins several physical processes of ENSO with reasonable time intervals. And the parameterized heating anomalies work better than the tropical mean SST anomalies for capturing the atmospheric temperature signal relative to ENSO.
2009, 26(2): 359-372. doi: 10.1007/s00376-009-0359-7
[Abstract](1054) [PDF 1020KB](1380)
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Based on an intermediate coupled model (ICM), a probabilistic ensemble prediction system (EPS) has been developed. The ensemble Kalman filter (EnKF) data assimilation approach is used for generating the initial ensemble conditions, and a linear, first-order Markov-Chain SST anomaly error model is embedded into the EPS to provide model-error perturbations. In this study, we perform ENSO retrospective forecasts over the 120 year period 1886--2005 using the EPS with 100 ensemble members and with initial conditions obtained by only assimilating historic SST anomaly observations. By examining the retrospective ensemble forecasts and available observations, the verification results show that the skill of the ensemble mean of the EPS is greater than that of a single deterministic forecast using the same ICM, with a distinct improvement of both the correlation and root mean square (RMS) error between the ensemble-mean hindcast and the deterministic scheme over the 12-month prediction period. The RMS error of the ensemble mean is almost 0.2oC smaller than that of the deterministic forecast at a lead time of 12 months. The probabilistic skill of the EPS is also high with the predicted ensemble following the SST observations well, and the areas under the relative operating characteristic (ROC) curves for three different ENSO states (warm events, cold events, and neutral events) are all above 0.55 out to 12 months lead time. However, both deterministic and probabilistic prediction skills of the EPS show an interdecadal variation. For the deterministic skill, there is high skill in the late 19th century and in the middle-late 20th century (which includes some artificial skill due to the model training period), and low skill during the period from 1906 to 1961. For probabilistic skill, for the three different ENSO states, there is still a similar interdecadal variation of ENSO probabilistic predictability during the period 1886--2005. There is high skill in the late 19th century from 1886 to 1905, and a decline to a minimum of skill around 1910--50s, beyond which skill rebounds and increases with time until the 2000s.
2009, 26(2): 352-358. doi: 10.1007/s00376-009-0352-1
[Abstract](827) [PDF 299KB](1032)
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Based on the Stratospheric Aerosol and Gas Experiment (SAGE) II and the Halogen Occultation Exper- iment (HALOE) ozone proles and the Total Ozone Mapping Spectrometer (TOMS) total ozone data sets, an empirical model for estimating the vertical distribution of stratospheric ozone over China is proposed. By using this model, the vertical distribution of stratospheric (16{50 km) ozone can be estimated according to latitude, month and total ozone. Comparisons are made between the modeled ozone proles and the SAGEII/HALOE monthly mean ozone measurements, and the results show that the model calculated ozone concentrations conform well with the SAGEII/HALOE measured values, with the dierences being less than 15% between 16 km and 18 km, less than 5% between 19 km and 40 km, and less than 10% between 41 km and 50 km. Comparisons of the model results with balloon-borne ozonesonde measurements performed in Beijing also show good agreement, within 5%, at altitudes between 19 km and 30 km.