FSS-based Evaluation on Monsoon Precipitation Forecasts in South China from Regional Models with Different Resolution

This study evaluated the forecast skill of CMA-GD 3 km and CMA-GD 1 km with hourly Rapid Update Cycle(RUC)for five monsoon precipitation events in South China from 2018 to 2020,using the fraction skill score(FSS)of the neighborhood spatial verification method.The results revealed that,among the 24-lead-hour forecasts in CMA-GD 3 km,the FSS for the 0.1 mm precipitation threshold increased linearly with the lead time from 3 to 1 hour,while there was no significant improvement in other lead times.For the 5 mm precipitation threshold,the forecast skill was highest for the latest 1-hour lead time,while the FSS showed slight variation between lead times of 24 hours and 8 hours.The FSS for 10 mm and 20 mm precipitation thresholds were similar to that of 5 mm,with the difference that the best score occurred at the 2-hour lead time.Among the 6-lead-hour forecasts in CMA-GD 1 km,the forecasts of the latest 1-hour lead time were the best choices for four precipitation thresholds.When comparing CMA-GD 3 km and CMA-GD 1 km,it was found that CMA-GD 3 km had better skill for forecasts of 0.1 mm and 5 mm precipitation at 2-hour and 1-hour lead times,while CMA-GD 1 km had better skill for all other forecasts,including the forecast of 20 mm precipitation nearly all lead hours(including 3-to 6-hour,and 1-hour lead times).The results suggest that the increased resolution of the model may be beneficial for precipitation forecasts in South China,especially for short-duration heavy precipitation over a longer lead hours.However,the limited sample size of this study calls for further evaluation using more cases to validate the results′generality.

An Assessment of Improvements in Global Monsoon Precipitation Simulation in FGOALS-s2

The performance of Version 2 of the Flexible Global Ocean-Atmosphere-Land System model （FGOALS-s2） in simulat ing global monsoon precipitation （GMP） was evaluated. Compared with FGOALS-sl, higher skill in simulating the annual modes of climatological tropical precipitation and interannual variations of GMP are seen in FGOALS-s2. The simulated domains of the northwestern Pacific monsoon （NWPM） and North American monsoon are smaller than in FGOALS-s 1. The main deficiency of FGOALS-s2 is that the NWPM has a weaker monsoon mode and stronger negatiw,＇ pattern in spring-fall asymmetric mode. The smaller NWPM domain in FGOALS-s2 is due to its simulated colder SST over the western Pacific warm pool. The relationship between ENSO and GMP is simulated reasonably by FGOALS-s2. However, the simulated precipitation anomaly over the South African monsoon region-South Indian Ocean during La Nina years is opposite to the observation. This results mainly from weaker warm SST anomaly over the maritime continent during La Nifia years, leading to stronger upper-troposphere （lower-troposphere） divergence （convergence） over the Indian Ocean, and artificial vertical as cent （descent） over the Southwest Indian Ocean （South African monsoon region）, inducing local excessive （deficient） rainfall. Comparison between the historical and pre-industrial simulations indicated that global land monsoon precipitation changes from 1901 to the 1970s were caused by internal variation of climate system. External forcing may have contributed to the increasing trend of the Australian monsoon since the 1980s. Finally, it shows that global warming could enhance GMR especially over the northern hemispheric ocean monsoon and southern hemispheric land monsoon.

Decreasing Trend in Global Land Monsoon Precipitation over the Past 50 Years Simulated by a Coupled Climate Model

The authors examine the effects of external forcing agents such as greenhouse gases （GHGs） and aerosols, as well as solar variability and ozone, on global land monsoon precipitation by using a coupled climate model HadGEM1, which was developed by the Met Office Hadley Centre for Climate Research. The results indicate that HadGEM1 performs well in simulating the observed decreasing trend of global land monsoon precipitation over the past 50 years. This trend mainly occurred in the Northern Hemisphere and is significantly different from the trend of natural variability due to ocean-atmosphere-land interactions. The coherence between the simulation and the observations indicates that the specified external forcing agents, including GHGs and aerosols as well as solar variability and ozone, are important factors that have affected the decreasing trend of global land monsoon precipitation in the past 50 years.

Forecasting Monsoon Precipitation Using Artificial Neural Networks

This paper explores the application of Artificial Intelligent (AI) techniques for climate forecast. It presents a study on modelling the monsoon precipitation forecast by means of Artificial Neural Networks (ANNs). Using the historical data of the total amount of summer rainfall over the Delta Area of Yangtze River in China, three ANNs models have been developed to forecast the monsoon precipitation in the corresponding area one year, five-year, and ten-year forward respectively. Performances of the models have been validated using a 'new' data set that has not been exposed to the models during the processes of model development and test. The experiment results are promising, indicating that the proposed ANNs models have good quality in terms of the accuracy, stability and generalisation ability.

Interdecadal Variability of East Asian Summer Monsoon Precipitation over 220 Years (1777-1997)

In this study, long-term （1777–1997） precipitation data for Seoul, Korea, wetness indices from eastern China, and modern observations are used to identify the interdecadal variability in East Asian summer monsoon precipitation over the last 220 years. In the East Asian monsoon region, two long-term timescales of dry–wet transitions for the interdecadal variability and quasi-40-and quasi-60-year timescales are dominant in the 220-year precipitation data of Seoul, as well as in the wetness indices over China. The wet and dry spells between Seoul （southern China） and northern China are out-of-phase （out-of-phase） at the quasi-60-year timescale, and in-phase （out-of-phase by approximately 90 ？ before 1900 and in-phase after 1900） at the quasi-40-year timescale. In particular, during the last century, the dominant long-term timescales over East Asia tend to decrease from the quasi-60-year to the quasi-40-year with increasing time. The dominant quasi-40-year and quasi-60-year timescales of the Seoul precipitation in Korea are strongly correlated with these timescales of the northern Pacific Ocean.

Impacts of Cumulus Convective Parameterization Schemes on Summer Monsoon Precipitation Simulation over China

By using the Betts-Miller-Janji＇c,Grell-Devenyi,and Kain-Fritsch cumulus convective parameterization schemes in the Weather Research and Forecasting（WRF） model,long time simulations from 2000 to 2009 are conducted to investigate the impacts of different cumulus convective parameterization schemes on summermonsoon precipitation simulation over China.The results show that all the schemes have the capability to reasonably reproduce the spatial and temporal distributions of summer monsoon precipitation and the corresponding background circulation.The observed north-south shift of monsoon rain belt is also well simulated by the three schemes.Detailed comparison indicates that the Grell-Devenyi scheme gives a better performance than the others.Deficiency in simulated water vapor transport is one possible reason for the precipitation simulation bias.

Analogue-Dynamical Prediction of Monsoon Precipitation in Northeast China Based on Dynamic and Optimal Configuration of Multiple Predictors

Based on the National Climate Center （NCC） of China operational seasonal prediction model results for the period 1983-2009 and the US National Weather Service Climate Prediction Center merged analysis of precipitation in the same period, together with the 74 circulation indices of NCC Climate System Diagnostic Division and 40 climate indices of NOAA of US during 1951 2009, an analogue-dynamical technique for objective and quantitative prediction of monsoon precipitation in Northeast China is proposed and implemented. Useful information is extracted from the historical data to estimate the model forecast errors. Dominant predictors and the predictors that exhibit evolving analogues are identified through cross validating the anomaly correlation coefficients （ACC） among single predictors, meanwhile with reference of the results from the dynamic analogue bias correction using four analogue samples. Next, an optimal configuration of multiple predictors is set up and compared with historical optimal multi-predictor configurations and then dynamically adjusted. Finally, the model errors are evaluated and utilized to correct the NCC operational seasonal prediction model results, and the forecast of monsoon precipitation is obtained at last. The independent sample validation shows that this technique has effectively improved the monsoon precipitation prediction skill during 2005 -2009. This study demonstrates that the analogue-dynamical approach is feasible in operational prediction of monsoon precipitation.

Distinct response of Northern Hemisphere land monsoon precipitation to transient and stablized warming scenarios

To better understand the climate response under stabilized,overshoot,and transient global warming,four types of ensemble experiments on 1.5℃/2℃ global warming scenarios(i.e.,stabilized 1.5℃,1.5℃ overshoot,stabilized 2℃,and transient 2℃)are elaborately designed using the Nanjing University Information Science and Technology Earth System Model(NESM).Compared with the modern climate(1985–2014),the projected surface air temperature(SAT)change is characterized by a robust‘Northern Hemisphere(NH)-warmer than-Southern Hemisphere(SH)’and‘land-warmer than-ocean’patterns.The projected precipitation change exhibits‘NH-wetter than-SH’pattern in the tropics.Although the response of SAT and precipitation climatology show similar pattern between stabilized and overshoot scenarios,some significant differences are still found.The projected change in the Northern Hemisphere land monsoon precipitation(NHLMP)is 30% larger in the transient 2℃ experiment compared with that in the stabilized 2℃ experiment.The more vigorous NHLMP in the transient global warming scenario is mainly due to the enhanced land-sea thermal contrast and interhemispheric temperature difference.The enlarged land-sea thermal contrast increases the surface pressure gradient between the NH continents and its adjacent oceans,thus enhancing the NH monsoon circulation and moisture convergence.The enhanced interhemispheric temperature difference shifts the Hadley circulation and intertropical convergence zone northward,leading to the enhanced moisture convergence and the shifts of tropical rain band over the NH monsoon region.This result highlights that climate responses may depend on different warming trajectories and,which could facilitate the strategic planning of governments.

Relationship Between Soil Temperature in May over Northwest China and the East Asian Summer Monsoon Precipitation

This study investigates the relationship between the soil temperature in May and the East Asian summer monsoon （EASM） precipitation in June and July using station observed soil temperature data over Northwest China from 1971 to 2000.It is found that the memory of the soil temperature at 80-cm depth can persist for at least 2 months,and the soil temperature in May is closely linked to the EASM precipitation in June and July.When the soil temperature is warmer in May over Northwest China,less rainfall occurs over the Yangtze and Huaihe River valley but more rainfall occurs over South China in June and July.It is proposed that positive anomalous soil temperature in May over Northwest China corresponds to higher geopotential heights over the most parts of the mainland of East Asia,which tend to weaken the ensuing EASM.Moreover,in June and July,a cyclonic circulation anomaly occurs over Southeast China and Northwest Pacific and an anticyclonic anomaly appears in the Yangtze and Huaihe River valley at 850 hPa.All the above tend to suppress the precipitation in the Yangtze and Huaihe River valley.The results also indicate that the soil temperature in May over Northwest China is closely related to the East Asia/Pacific （EAP） teleconnection pattern,and it may be employed as a useful predictor for the East Asian summer monsoon rainfall.

Variations in monsoon precipitation over southwest China during the last 1500 years and possible driving forces

Understanding hydroclimatic patterns and their possible driving mechanisms during distinct climate periods over the last 1500 years—such as the Medieval Warm Period(MWP),the Little Ice Age(LIA),and the Current Warm Period—is crucial for predicting future changes to monsoon precipitation in southwest China under global warming scenarios.In this study,based on ^(210)Pb and ^(137)Cs dating of surface sediments and AMS ^(14)C dating of terrestrial plant residues,we establish a robust age model that covers the last~1500 years(AD 439–2012)at Lake Yihai in southwest China.We use analyses of multiple geochemical proxy indices,including loss on ignition at 550℃,total organic carbon,total nitrogen,C/N ratios,and stable carbon isotopes of organic matter to reconstruct changes in summer monsoon precipitation at Lake Yihai during the last~1500 years.The results show that,over southwest China,warm and dry climate conditions prevailed during the MWP(AD 1000–1400)and the past 200 years,whereas conditions during the LIA(AD 1400–1800)were cold and wet.This is consistent with evidence from other geological records over southwest China,such as stalagmite and lake sediment data.Similar hydroclimatic patterns have occurred over the last 1500 years in adjacent tropical/subtropical monsoon regions where the climate is similarly dominated by the Indian summer monsoon(e.g.,South China,the South China Sea,Southeast Asia,Northeast India).We suggest that the meridional migration of the mean position of the Inter-tropical Convergence Zone,and El Niño/Southern Oscillation conditions which are linked to tropical Pacific sea surface temperature,are responsible for centennial-scale hydroclimatic patterns over southwest China and adjacent areas during the last 1500 years.

Precipitation Distribution of the Extended Global Spring-Autumn Monsoon and Its Possible Formation Mechanism

The global monsoon(GM)comprises two major modes,namely,the solstitial mode and equinoctial asymmetric mode.In this paper,we extend the GM domain from the tropics to the global region and name it the global spring-autumn monsoon(GSAM),which mainly indicates a spring-autumn asymmetrical precipitation pattern exhibiting annual variation.Its distribution and possible formation mechanisms are also analyzed.The GSAM domain is mainly distributed over oceans,located both in the midlatitude and tropical regions of the Pacific and Atlantic.In the GSAM domains of both the Northern and Southern Hemispheres,more precipitation occurs in local autumn than in local spring.The formation mechanisms of GSAM precipitation vary according to the different domains.GSAM precipitation in the tropical domain of the Eastern Hemisphere is influenced by the circulation differences between the onset and retreat periods of the Asian summer monsoon,while tropical cyclone activities cause precipitation over the South China Sea(SCS)and western North Pacific(WNP).GSAM precipitation in the tropical domain of the Western Hemisphere is influenced by the tropical asymmetrical circulation between the Northern and Southern Hemispheres and the variation in the intertropical convergence zone(ITCZ)driven by the intensity of the sea surface temperature cold tongues over the equatorial eastern Pacific and eastern Atlantic.GSAM precipitation in the midlatitude domain is influenced by the differences in water vapor transportation and convergence between spring and autumn.In addition,GSAM precipitation is also affected by extratropical cyclone activities.

THE MONSOON PRECIPITATION VARIATION IN THE CLIMATE CHANGE

First,studies on the East Asian monsoon simulation were reviewed.Then the monsoon precipitation change in the paleoclimate was simulated and analyzed.This paper also analyzed and simulated the interannual changes of monsoon precipitation and their relations with the sea surface temperature (SST) changes.Finally,the simulated monsoon precipi- tation change in the CO_2-induced climate change was discussed.

Statistical Downscaling for Multi-Model Ensemble Prediction of Summer Monsoon Rainfall in the Asia-Pacific Region Using Geopotential Height Field

The 21-yr ensemble predictions of model precipitation and circulation in the East Asian and western North Pacific （Asia-Pacific） summer monsoon region （0°-50°N, 100° 150°E） were evaluated in nine different AGCM, used in the Asia-Pacific Economic Cooperation Climate Center （APCC） multi-model ensemble seasonal prediction system. The analysis indicates that the precipitation anomaly patterns of model ensemble predictions are substantially different from the observed counterparts in this region, but the summer monsoon circulations are reasonably predicted. For example, all models can well produce the interannual variability of the western North Pacific monsoon index （WNPMI） defined by 850 hPa winds, but they failed to predict the relationship between WNPMI and precipitation anomalies. The interannual variability of the 500 hPa geopotential height （GPH） can be well predicted by the models in contrast to precipitation anomalies. On the basis of such model performances and the relationship between the interannual variations of 500 hPa GPH and precipitation anomalies, we developed a statistical scheme used to downscale the summer monsoon precipitation anomaly on the basis of EOF and singular value decomposition （SVD）. In this scheme, the three leading EOF modes of 500 hPa GPH anomaly fields predicted by the models are firstly corrected by the linear regression between the principal components in each model and observation, respectively. Then, the corrected model GPH is chosen as the predictor to downscale the precipitation anomaly field, which is assembled by the forecasted expansion coefficients of model 500 hPa GPH and the three leading SVD modes of observed precipitation anomaly corresponding to the prediction of model 500 hPa GPH during a 19-year training period. The cross-validated forecasts suggest that this downscaling scheme may have a potential to improve the forecast skill of the precipitation anomaly in the South China Sea, western North Pacific and the East Asia Pacific regions, where the anomaly correlation coefficient （ACC） has been improved by 0.14, corresponding to the reduced RMSE of 10.4% in the conventional multi-model ensemble （MME） forecast.

Variable and Robust East Asian Monsoon Rainfall Response to El Nio over the Past 60 Years(1957–2016)

Severe flooding occurred in southern and northern China during the summer of 2016 when the 2015 super El Nio decayed to a normal condition. However, the mean precipitation during summer（June–July-August） 2016 does not show significant anomalies, suggesting that — over East Asia（EA） — seasonal mean anomalies have limited value in representing hydrological hazards. Scrutinizing season-evolving precipitation anomalies associated with 16 El Nio episodes during 1957–2016 reveals that, over EA, the spatiotemporal patterns among the four categories of El Nio events are quite variable, due to a large range of variability in the intensity and evolution of El Nio events and remarkable subseasonal migration of the rainfall anomalies. The only robust seasonal signal is the dry anomalies over central North China during the El Nio developing summer. Distinguishing strong and weak El Nio impacts is important. Only strong El Nio events can persistently enhance EA subtropical frontal precipitation from the peak season of El Nio to the ensuing summer, by stimulating intense interaction between the anomalous western Pacific anticyclone（WPAC） and underlying dipolar sea surface temperature anomalies in the Indo-Pacific warm pool, thereby maintaining the WPAC and leading to a prolonged El Nio impact on EA. A weak El Nio may also enhance the post-El Nio summer rainfall over EA, but through a different physical process： the WPAC re-emerges as a forced response to the rapid cooling in the eastern Pacific. The results suggest that the skillful prediction of rainfall over continental EA requires the accurate prediction of not only the strength and evolution of El Nio, but also the subseasonal migration of EA rainfall anomalies.

THE DIRECT EFFECTS OF AEROSOLS AND DECADAL VARIATION OF GLOBAL SEA SURFACE TEMPERATURE ON THE EAST ASIAN SUMMER PRECIPITATION IN CAM3.0

Using the CAM3.0 model, we investigated the respective effects of aerosol concentration increasing and decadal variation of global sea surface temperature(SST) around year 1976/77 on the East Asian precipitation in boreal summer. By doubling the concentration of the sulfate aerosol and black carbon aerosol separately and synchronously in East Asia(100-150 °E, 20-50 °N), the climate effects of these aerosols are specifically investigated. The results show that both the decadal SST changing and aerosol concentration increasing could lead to rainfall decreasing in the center of East Asia, but increasing in the regions along southeast coast areas of China. However, the different patterns of rainfall over ocean and lower wind field over Asian continent between aerosol experiments and SST experiments in CAM3.0 indicate the presence of different mechanisms. In the increased aerosol concentration experiments, scattering effect is the main climate effect for both sulfate and black carbon aerosols in the Eastern Asian summer. Especially in the increased sulfate aerosol concentration experiment, the climate scattering effect of aerosol leads to the most significant temperature decreasing, sinking convection anomalies and decreased rainfall in the troposphere over the central part of East Asia. However, in an increased black carbon aerosol concentration experiment, weakened sinking convection anomalies exist at the southerly position. This weakened sinking and its compensating rising convection anomalies in the south lead to the heavy rainfall over southeast coast areas of China. When concentrations of both sulfate and black carbon aerosols increase synchronously, the anomalous rainfall distribution is somewhat like that in the increased black carbon concentration aerosol experiment but with less intensity.

Effect of climate change on seasonal monsoon in Asia and its impact on the variability of monsoon rainfall in Southeast Asia

Global warming and climate change is one of the most extensively researched and discussed topical issues affecting the environment.Although there are enough historical evidence to support the theory that climate change is a natural phenomenon,many research scientists are widely in agreement that the increase in temperature in the 20 th century is anthropologically related.The associated effects are the variability of rainfall and cyclonic patterns that are being observed globally.In Southeast Asia the link between global warming and the seasonal atmospheric flow during the monsoon seasons shows varying degree of fuzziness.This study investigates the impact of climate change on the seasonality of monsoon Asia and its effect on the variability of monsoon rainfall in Southeast Asia.The comparison of decadal variation of precipitation and temperature anomalies before the 1970 s found general increases which were mostly varying.But beyond the 1970 s,global precipitation anomalous showed increases that almost corresponded with increases in global temperature anomalies for the same period.There are frequent changes and a shift westward of the Indian summer monsoon.Although precipitation is observed to be 70%below normal levels,in some areas the topography affects the intensity of rainfall.These shifting phenomenon of other monsoon season in the region are impacting on the variability of rainfall and the onset of monsoons in Southeast Asia and is predicted to delay for 15 days the onset of the monsoon in the future.The variability of monsoon rainfall in the SEA region is observed to be decadal and the frequency and intensity of intermittent flooding of some areas during the monsoon season have serious consequences on the human,financial,infrastructure and food security of the region.

Antarctica Sea-ice Oscillation and Its Possible Impact on Monsoon of South Sea

Antarctic sea-ice oscillation index with a seesaw pattern is defined using NCEP/NCAR reanalysis girds data of monthly Antarctica sea-ice concentration from 1979 to 2002.The relationships between the index of winter and the summer precipitations in China as well as the onset date of the summer East Asia monsoon are presented.The study result shows that the grids of correlation coefficients passed 5% confidence level between Antarctic sea-ice oscillation index and Antarctic sea-ice concentration are more than 1/3 of all grids of Antarctica sea-ice,that means the index can represent 1/3 sea-ice area.The winter index has a significant correlation with abnormal summer（June-August） precipitation in China.The area of positive correlation lies in the Yangtze River basin and its south,and that of negative correlation lies mainly in the north of Yangtze River basin.While the winter index is positive（negative）,the onset date of South China Sea monsoon is earlier（later）,with a probability of 79%（80%）.Consequently, a conceptual model is given in term of discussing the possible process between the winter Antarctic sea ice and the monsoon precipitation in China.

Changed Relationships Between the East Asian Summer Monsoon Circulations and the Summer Rainfall in Eastern China

In previous statistical forecast models,prediction of summer precipitation along the Yangtze River valley and in North China relies heavily on its close relationships with the western Pacific subtropical high（WPSH）,the blocking high in higher latitudes,and the East Asian summer monsoon（EASM）.These relationships were stable before the 1990 s but have changed remarkably in the recent two decades.Before the 1990 s,precipitation along the Yangtze River had a significant positive correlation with the intensity of the WPSH,but the correlation weakened rapidly after 1990,and the correlation between summer rainfall in North China and the WPSH also changed from weak negative to significantly positive.The changed relationships present a big challenge to the application of traditional statistical seasonal prediction models.Our study indicates that the change could be attributed to expansion of the WPSH after around 1990.Owing to global warming,increased sea surface temperatures in the western Pacific rendered the WPSH stronger and further westward.Under this condition,more moisture was transported from southern to northern China,leading to divergence and reduced（increased） rainfall over the Yangtze River（North China）.On the other hand,when the WPSH was weaker,it stayed close to its climatological position（rather than more eastward）,and the circulations showed an asymmetrical feature between the stronger and weaker WPSH cases owing to the decadal enhancement of the WPSH.Composite analysis reveals that the maximum difference in the moisture transport before and after 1990 appeared over the western Pacific.This asymmetric influence is possibly the reason why the previous relationships between monsoon circulations and summer rainfall have now changed.

Observational and Modeling Studies of Impacts of the South China Sea Monsoon on the Monsoon Rainfall in the Middle-Lower Reaches of the Yangtze River During Summer

Based on the ERA-40 and NCEP/NCAR reanalysis data,the NOAA Climate Prediction Center＇s merged analysis of precipitation（CMAP）,and the fifth-generation PSU/NCAR Mesoscale Model version 3（MM5v3）,we defined a monsoon intensity index over the East Asian tropical region and analyzed the impacts of summer（June-July） South China Sea（SCS） monsoon anomaly on monsoon precipitation over the middle-lower reaches of the Yangtze River（MLRYR） using both observational data analysis and numerical simulation methods.The results from the data analysis show that the interannual variations of the tropical monsoon over the SCS are negatively correlated with the southwesterly winds and precipitation over the MLRYR during June-July.Corresponding to stronger（weaker） tropical monsoon and precipitation,the southwesterly winds are weaker（stronger） over the MLRYR,with less（more） local precipitation.The simulation results further exhibit that when changing the SCS monsoon intensity,there are significant variations of monsoon and precipitation over the MLRYR.The simulated anomalies generally consist with the observations,which verifies the impact of the tropical monsoon on the monsoon precipitation over the MLRYR.This impact might be supported by certain physical processes.Moreover,when the tropical summer monsoon is stronger,the tropical anomalous westerly winds and positive precipitation anomalies usually maintain in the tropics and do not move northward into the MLRYR,hence the transport of water vapor toward southern China is weakened and the southwest flow and precipitation over southern China are also attenuated.On the other hand,the strengthened tropical monsoon may result in the weakening and southward shift of the western Pacific subtropical high through self-adjustment of the atmospheric circulation,leading to the weakening of the monsoon flows and precipitation over the MLRYR.