VERIFICATION OF TROPICAL CYCLONE RAINFALL PREDICTIONS FROM CMA AND JMA GLOBAL MODELS

The number of tropical cyclone (TC) genesis over the South China Sea and the Northwest Pacific Ocean in 2009 is significantly less than the average (27.4). However, the number of landfall TC over mainland China and its associated rainfall is more than the average. This paper focuses on the performance of numerical weather prediction (NWP) of landfall TC precipitation over China in 2009. The China Meteorological Administration (CMA) and Japan Meteorological Agency (JMA) models are compared. Although the schemes of physical processes, the data assimilation system and the dynamic frame are entirely different for the two models, the results of forecast verification are similar to each other for TC rainfall and track except for TC Goni. In this paper, a day with daily rainfall amount greater than 50 mm was selected as a storm rain day when there was a TC affecting the mainland. There are 32 storm rain days related to the landing of typhoons and tropical depressions. The rainfall forecast verification methods of National Meteorological Centre (NMC) of CMA are selected to verify the models’ rainfall forecast. Observational precipitation analyses related to TCs in 2009 indicate a U-shape spatial distribution in China. It is found that the rain belt forecasted by the two models within 60 hours shows good agreement with observations, both in the location and the maximum rainfall center. Beyond 3 days, the forecasted rainfall belt shifts northward on average, and the rainfall amount of the model forecasts becomes under-predicted. The rainfall intensity of CMA model forecast is more reasonable than that of JMA model. For heavy rain, the JMA model made more missing forecasts. The TC rainfall is verified in Guangdong, Guangxi, Fujian and Hainan where rainfall amount related to TCs is relatively larger than in other regions. The results indicate that the model forecast for Guangdong and Guangxi is more skillful than that for Hainan. The rainfall forecast for Hainan remains difficult for the models because of insufficient observation data and special tropical ocean climate.     

A New Method to Compare Hourly Rainfall between Station Observations and Satellite Products over Central–Eastern China

This study employs a newly defined regional-rainfall-event(RRE) concept to compare the hourly characteristics of warm-season(May–September) rainfall among rain gauge observations, China merged hourly precipitation analysis(CMPA-Hourly), and two commonly used satellite products(TRMM 3B42 and CMORPH).By considering the rainfall characteristics in a given limited area rather than a single point or grid, this method largely eliminates the differences in rainfall characteristics among different observations or measurements over central–eastern China. The results show that the spatial distribution and diurnal variation of RRE frequency and intensity are quite consistent among different datasets, and the performance of CMPAHourly is better than the satellite products when compared with station observations. A regional rainfall coefficient(RRC), which can be used to classify local rain and regional rain, is employed to represent the spatial spread of rainfall in the limited region defining the RRE. It is found that rainfall spread in the selected grid box is more uniform during the nocturnal to morning hours over central–eastern China. The RRC tends to reach its diurnal maximum several hours after the RRE intensity peaks, implying an intermediate transition stage from convective to stratiform rainfall. In the afternoon, the RRC reaches its minimum, implying the dominance of local convections on small spatial scale in those hours, which could cause large differences in rain gauge and satellite observations. Since the RRE method reflects the overall features of rainfall in a limited region rather than at a fixed point or in a single grid, the widely recognized overestimation of afternoon rainfall in satellite products is not obvious, and thus the satellite estimates are more reliable in representing sub-daily variation of rainfall from the RRE perspective. This study proposes a reasonable method to compare satellite products with rain gauge observations on the sub-daily scale,which also has great potential to be used in evaluating the spatiotemporal variation of cloud and rainfall in numerical models.     

A COMPOSITE STUDY OF RAINFALL ASYMMETRY OF TROPICAL CYCLONES AFTER MAKING LANDFALL IN GUANGDONG PROVINCE

Based on observed rainfall data, this study makes a composite analysis of rainfall asymmetry in tropical cyclones(TCs) after making landfall in Guangdong province(GD) during 1998—2015. There are 3.0 TCs per year on average making landfall in GD and west of GD(WGD) has the most landfall TCs. Most of TCs make landfall in June,July, August, and September at the intensities of TY, STS, and TS. On average, there is more rainfall in the southwest quadrant of TC in CGD(center of GD), WGD, and GD as a whole, and the maximum rainfall is located in the southwest near the TC center. The mean TC rainfall in the east of GD(EGD) leans to the eastern side of TC. The TC rainfall distributions in June, July, August, and September all lean to the southwest quadrant and the maximum rainfall is located in the southwest near the TC center. The same features are found in the mean rainfall of TD, TS, STS, TY,and STY. The maximum rainfall is mainly in the downshear of vertical wind shear. Vertical wind shear is probably the dominate factor that determines asymmetric rainfall distribution of TCs in GD. Storm motion has little connection with TC rainfall asymmetry in GD.     

Diurnal Variation in the Vertical Profile of the Raindrop Size Distribution for Stratiform Rain as Inferred from Micro Rain Radar Observations in Sumatra

The diurnal variation in the vertical structure of the raindrop size distribution(RSD) associated with stratiform rain at Kototabang, West Sumatra(0.20°S, 100.32°E), was investigated using micro rain radar(MRR) observations from January 2012 to August 2016. Along with the MRR data, the RSD from an optical disdrometer and vertical profile of precipitation from the Tropical Rainfall Measuring Mission were used to establish the microphysical characteristics of diurnal rainfall.Rainfall during 0000–0600 LST and 1800–2400 LST had a lower concentration of small drops and a higher concentration of large drops when compared to rainfall during the daytime(0600–1800 LST). The RSD stratified on the basis of rain rate(R) showed a lower total concentration of drops and higher mass-weighted mean diameter in 0000–0600 LST and1800–2400 LST than in the daytime. During the daytime, the RSD is likely governed by a riming process that can be seen from a weak bright band(BB). On the other hand, during 0000–0600 LST and 1800–2400 LST, the BB was stronger and the rainfall was associated with a higher concentration of midsize and large drops, which could be attributed to more active aggregation right above the melting layer with minimal breakup. Diurnal variation in the vertical profile of RSD led to a different radar reflectivity(Z)–R relationship in the rain column, in which Z during the periods 0000–0600 LST and1800–2400 LST was larger than at the other times, for the same R.     

The Seasonal and Interannual Variation of Diurnal Precipitation over the Tibetan Plateau and Its Downstream Regions Observed by the Tropical Rainfall Measuring Mission

Using nine years of Tropical Rainfall Measuring Mission(TRMM)2A25 data,based on the probability density function of rainfall,a comparative analysis of the diurnal cycle and its seasonal and interannual variation for convective rain,stratiform rain,and total rain is made between the Tibetan Plateau and the downstream Yangtze River basin and East China Sea.The diurnal convective rain is stronger than the diurnal stratiform rain over the Yangtze River basin,and the convective rain peaks in the afternoon when the stratiform rain maximum happens in the early morning.Convective rain and stratiform rain both peak in the early morning over the East China Sea.The diurnal total rain over the Tibetan Plateau is stronger than its downstream regions.The diurnal cycle appears quite different among the four seasons over the Yangtze River basin,and the seasonal variation of diurnal convective rain is more apparent than diurnal stratiform rain.The seasonal variation of the diurnal cycle is weak over the East China Sea and Tibetan Plateau.The maximum of total rain happens in the afternoon during1998–2002 over the Yangtze River basin,while it peaks in the early morning during 2003–2006,but no obvious phase differences can be found among years in the diurnal rain over the East China Sea and over the Tibetan Plateau.     

Influence of the Mascarene High and Australian High on the Summer Monsoon in East Asia： Ensemble Simulation

By using a nine-level atmospheric general circulation model developed at the Institute of Atmospheric Physics (IAP 9L AGCM), two sets of numerical experiments are carried out to investigate the influence of the Mascarene high (MH) and Australian high (AH) over the southern subtropics upon the East Asian summer monsoon circulation and summer precipitation in East Asia. The use of ensemble statistics is adopted to reduce the simulation errors. The result shows that with the intensification of MH, the Somali low-level jet is significantly enhanced together with the summer monsoon circulation in the tropical Asia and western Pacific region. Furthermore, the anticyclonic anomaly in the tropical western Pacific to the east of the Philippines may induce a weak East-Asia-Pacific teleconnection pattern. In the meantime,geopotential height in the Tropics is enhanced while it is reduced over most regions of mid-high latitudes,thus the northwestern Pacific subtropical high at 500 hPa extends southwestward, resulting in more rainfall in southern China and less rainfall in northern China. A similar anomaly pattern of the atmospheric circulation systems is found in the experiment of the intensification of AH. On the other hand, because the cross-equatorial currents associated with AH are much weaker than the Somali jet, the anomaly magnitude caused by the intensification of AH is generally weak, and the influence of AH on summer rainfall in China seems to be localized in southern China. Comparison between the two sets of experiments indicates that MH plays a crucial role in the interactions of general atmospheric circulation between the two hemispheres.     

东亚夏季风的年际到年代际变化及其与全球大气环流和海表温度的联系

The East Asian summer monsoon (EASM) underwent an interdecadal variation with interannual variations during the period from 1958 to 1997, its index tended to decline from a higher stage in the mid-1960＇s until it reached a lower stage after 1980＇s. Correlation analysis reveals that EASM is closely related with the global atmospheric circulation and sea surface temperature (SST). The differences between the weak and strong stage of EASM shows that, the summer monsoon circulation over East Asia and North Africa is sharply weakened, in the meantime, the westerlies in high latitudes and the trade--wind over the tropical ocean are also changed significantly. Over the most regions south of the northern subtropics, both air temperature in the lower troposphere and SST tended to rise compared with the strong stage of EASM. It is also revealed that the ocean-atmosphere interaction over the western Pacific and Indian Ocean plays a key role in interannual to interdecadal variation of EASM, most probably, the subtropical Indian Ocean is more important. On the other hand, the ENSO event is less related to EASM at least during the concerned period.     

AN OPERATIONAL STATISTICAL SCHEME FOR TROPICAL CYCLONE INDUCED RAINFALL FORECAST

A non-parametric method is used in this study to analyze and predict short-term rainfall due to tropical cyclones(TCs) in a coastal meteorological station. All 427 TCs during 1953-2011 which made landfall along the Southeast China coast with a distance less than 700 km to a certain meteorological station- Shenzhen are analyzed and grouped according to their landfalling direction, distance and intensity. The corresponding daily rainfall records at Shenzhen Meteorological Station(SMS) during TCs landfalling period(a couple of days before and after TC landfall) are collected. The maximum daily rainfall(R-24) and maximum 3-day accumulative rainfall(R-72) records at SMS for each TC category are analyzed by a non-parametric statistical method, percentile estimation. The results are plotted by statistical boxplots, expressing in probability of precipitation. The performance of the statistical boxplots is evaluated to forecast the short-term rainfall at SMS during the TC seasons in 2012 and 2013. Results show that the boxplot scheme can be used as a valuable reference to predict the short-term rainfall at SMS due to TCs landfalling along the Southeast China coast.     

CONVECTIVE ANOMALIES IN TROPICAL OCEAN AREAS AND LONG-LEAD FORECAST OF SUMMER RAINFALL IN SHANDONG

This study focuses on deep convection anomalies in tropical regions in winter-spring period and their possible influence on the following summer rainfall in Shandong province. On the basis of monthly precipitation wet and dry summers in Shandong are defined according to a precipitation index. Then monthly OLR data, observed by NOAA satellites, are used to diagnose the features of deep convection for both wet and dry summers. It is found that negative anomalies seem dominant prior to wet summers, while large areas of positive anomalies appear prior to dry summers in tropical oceans. The differences are remarkable especially in the western, middle and eastern tropical Pacific as well as in the tropical Indian Ocean. Correlative analysis confirms the relations between OLR and precipitation. Subtropical High, which plays an essential role in summer rainfall, is also connected with the deep conviction. Altogether eight EOF-CCA forecast models are established on the basis of the above study. The assessment of the models relies on the gauge observing precipitation in 1997 and 1998. The results show that models using spring OLR data appear to be more practicable than those using winter OLR data, and the models established with OLR in western Pacific and the Indian Ocean perform better than the others.     

OPERATIONAL FORECAST OF RAINFALL INDUCED BY LANDFALLING TROPICAL CYCLONES ALONG GUANGDONG COAST

Following previous studies of the rainfall forecast in Shenzhen owing to landfalling tropical cyclones(TCs), a nonparametric statistical scheme based on the classification of the landfalling TCs is applied to analyze and forecast the rainfall induced by landfalling TCs in the coastal area of Guangdong province, China. All the TCs landfalling with the distance less than 700 kilometers to the 8 coastal stations in Guangdong province during 1950—2013 are categorized according to their landfalling position and intensity. The daily rainfall records of all the 8 meteorological stations are obtained and analyzed. The maximum daily rainfall and the maximum 3 days' accumulated rainfall at the 8 coastal stations induced by each category of TCs during the TC landfall period(a couple of days before and after TC landfalling time) from 1950 to 2013 are computed by the percentile estimation and illustrated by boxplots. These boxplots can be used to estimate the rainfall induced by landfalling TC of the same category in the future. The statistical boxplot scheme is further coupled with the model outputs from the European Centre for Medium-Range Weather Forecasts(ECMWF) to predict the rainfall induced by landfalling TCs along the coastal area. The TCs landfalling in south China from 2014 to 2017 and the corresponding rainfall at the 8 stations area are used to evaluate the performance of these boxplots and coupled boxplots schemes. Results show that the statistical boxplots scheme and coupled boxplots scheme can perform better than ECMWF model in the operational rainfall forecast along the coastal area in south China.     

Warm-Season Diurnal Variations of Total,Stratiform, Convective,and Extreme Hourly Precipitation over Central and Eastern China

Diurnal variations in amount, frequency and intensity of warm-season hourly precipitation(HP) at seven levels, which are defined as HP 0.1, 0.5, 1, 5, 10, 20 and 50 mm, are revealed based on no less than 30 years of hourly rain-gauge observations at national stations over central and eastern China(CEC). This study investigates the variations, relationships, differences and similarities of total, stratiform, convective and extreme HP over the entire CEC and various subregions. Results indicate that the variations in the amount and frequency of HP at the seven levels over the entire CEC all display a bimodal feature. For various regions, the variations of total HP mostly feature two peaks, while convective HP mainly occurs in the late afternoon and determines the diurnal variation of total HP intensity. On the basis of the primary peak time periods of HP frequency at all levels over different subregions, the variations can be classified into three main categories: late-afternoon primary peak, nocturnal primary peak, and time-shifting primary peak. However, the variations over some coastal regions like the Liaodong Peninsula, the Shandong Peninsula, and the coastal regions of Guangdong, distinctly differ from those over their corresponding larger regions. Overall, the normalized diurnal variation amplitude of amount and frequency increases with the increasing HP intensity; convective precipitation can be represented by HP 10 mm; and the intensity of HP 50 mm is slightly larger during the nighttime than during the daytime over the entire CEC. In northern China, diurnal variation in HP 5 mm can represent well that in convective precipitation.     

The Impact of Orographically-Induced Gravity Wave on the Diurnal Cycle of Rainfall over Southeast Kalimantan Island

Precipitation measurements from the Tropical Rainfall Measuring Mission (TRMM) satellite indicate that the southeastern area of Kalimantan (Borneo) Island receives much less rainfall than elsewhere on the island during the period from July to October.Results from sur-face meteorological observations show that the diurnal cycle of rainfall differs greatly between the eastern and western coasts of the island.Rainfall on the western coast of the island is frequent in the afternoon and evening,whereas almost all rainfall on the eastern coast occurs in the morning.Meanwhile,the Global Positioning System (GPS)-derived precipitable water (PW) on the eastern coast shows a substantial decrease in moisture in the af-ternoon and evening.Numerical experiments with a mesoscale model reveal that gravity waves driven by di-urnal heating of the elevated land surface of the moun-tains on Sulawesi Island,which lies approximately 300 kilometers to the east of Kalimantan Island,significantly affect the diurnal cycle of rainfall over southeast Kali-mantan Island.     

Diurnal Variations of Precipitation over North China Regulated by the Mountain-plains Solenoid and Boundary-layer Inertial Oscillation

The mountain-plains solenoid(MPS) and boundary-layer inertial oscillation(BLO) are two typical regional forcings at the diurnal time scale. Their relative role in regulating the diurnal variations of summer rainfall over North China and their change under different monsoon conditions are studied using a 19-yr archive of satellite rainfall and reanalysis data. It is shown that both a strong MPS and BLO can increase nocturnal rainfall in the North China plains but exhibit evident regional differences. The MPS-induced nocturnal rainfall is relatively confined to the plains adjacent to mountains from late night to morning, due to the upward branch of the nighttime MPS. In contrast, the BLO-induced nocturnal rainfall strengthens from early evening and is more extensive in early morning over the open plains further east. The contrasting effect in the evening is related to the convergent(divergent) easterly anomaly in the plains under the BLO(MPS). The BLO also induces the relatively strong enhancement of moisture convergence and high humidity by the southerly anomaly at late night. On strong monsoon days, the nocturnal rainfall amount associated with the MPS and BLO increases considerably in the plains.Both regional forcings become effective in regulating the rainfall diurnal cycle with enhanced moisture convergence under monsoon conditions. Their induced diurnal amplitudes of moisture convergence can be comparable to the daily mean by monsoon flow. The regional forcings thus couple with monsoon flow to strengthen rainfall in the plains, particularly from late night to morning. The results highlight that a combination of regional and large-scale forcings can strongly regulate the warm-season climate.     

Simulation and Projection of Changes in Rainy Season Precipitation over China Using the WRF Model

The Weather Research and Forecasting (WRF) model is used in a regional climate model configuration to simulate past precipitation climate of China during the rainy season (May-September) of 1981-2000, and to investigate potential future (2041-2060 and 2081-2100) changes in precipitation over China relative to the reference period 1981-2000. WRF is run with initial conditions from a coupled general circulation model, i.e., the high-resolution version of MIROC (Model for Interdisciplinary Research on Climate). WRF reproduces the observed distribution of rainy season precipitation in 1981-2000 and its interannual variations better than MIROC. MIROC projects increases in rainy season precipitation over most parts of China and decreases of more than 25 mm over parts of Taiwan and central Tibet by the mid-21st century. WRF projects decreases in rainfall over southern Tibetan Plateau, Southwest China, and northwestern part of Northeast China, and increases in rainfall by more than 100 mm along the southeastern margin of the Tibetan Plateau and over the lower reaches of the Yangtze River during 2041-2060. MIROC projects further increases in rainfall over most of China by the end of the 21st century, although simulated rainfall decreases by more than 25 mm over parts of Taiwan, Guangxi, Guizhou, and central Tibet. WRF projects increased rainfall of more than 100 mm along the southeastern margin of the Tibetan Plateau and over the lower reaches of the Yangtze River and decreased rainfall over Southwest China, and southern Tibetan Plateau by the end of the 21st century.     

THE RELATIONSHIP BETWEEN SOUTH CHINA SEA SOUTHWEST MONSOON ANOMALIES AND IMPORTANT WEATHER IN GUANGDONG PROVINCE DURING THE RAINING SEASONS

The activity of South China Sea southwest monsoon (SCSSM) has direct impacts on the anomalies of important weather in Guangdong province during the raining seasons. So it is necessary to explore thoroughly the activity pattern of SCSSM and its relationship with important weather anomalies in the province. In this paper, the methods of composite analysis and correlation statistics are used to study the relationship between the onset date and intensity of SCSSM and the important weather, such as precipitation trends in Guangdong province during the annually first and second raining seasons, the timing of the annually first and last typhoon and the number of typhoons landing in Guangdong province. The results show that the rainfall is less than normal during the first raining season, but more than normal during the second one and there are more tropical cyclones landing in Guangdong province in the years of early SCSSM onset. The rainfall is more than normal during the second raining season and there are more tropical cyclones landing in Guangdong province in the years of strong SCSSM. The relationship between the SST of April - June, July - September and previous winter (December - February) and 500 hPa geopotential height and the onset date and intensity of SCSSM is analyzed. Some mechanisms between the onset dates and intensity of SCSSM and the important weather anomalies in Guangdong province are preliminarily explored. The results can be used for reference in short-term climate forecast.     

Relationship between winter snow cover days in Northeast China and rainfall near the Yangtze River basin in the following summer

Based on observed snow and precipitation data and NCEP/NCAR reanalysis data,the relationship between the number of winter snow cover days in Northeast China and the following summer’s rainfall in the northern part of southern China is analyzed and the possible underlying mechanisms are discussed.The results indicate that a negative relationship is significant throughout the study period,especially more obvious after the 1980s.The pre-winter circulation patterns in years with more snow cover days and less summer rainfall in the south bank of the Yangtze River are almost the same.In years with more snow cover days,lower temperatures at the lower level over Northeast China are found in winter and spring.The winter monsoon is weaker and retreats later in these years than in those with fewer snow cover days.In spring of years with more snow cover days,anomalous cyclonic circulation is observed over Northeast China,and anomalous northerly wind is found in eastern China.In summer of these years,anomalous northeasterly wind at the lower level is found from the area south of the Yangtze River to the East China Sea and Yellow Sea;and with less southwesterly water vapor transport,the rainfall in the area south of the Yangtze River is less than normal,and the opposite patterns are true in years with fewer snow cover days.In recent years,the stable relationship between winter snow cover in Northeast China and summer rainfall in the Yangtze River basin can be used for summer rainfall prediction.The results are of great importance to short-term climate prediction for summer rainfall.     

The Role of β-effect and a Uniform Current on Tropical Cyclone Intensity

A limited-area primitive equation model is used to study the role of the β-effect and a uniform current on tropical cyclone (TC) intensity.It is found that TC intensity is reduced in a non-quiescent environment compared with the case of no uniform current.On an f-plane,the rate of intensification of a tropical cyclone is larger than that of the uniform flow.A TC on a β-plane intensifies slower than one on an f-plane.The main physical characteristic that distinguishes the experiments is the asymmetric thermodynamic (including convective) and dynamic structures present when either a uniform flow or β-effect is introduced.But a fairly symmetric TC structure is simulated on an f-plane.The magnitude of the warm core and the associated subsidence are found to be responsible for such simulated intensity changes.On an f-plane,the convection tends to be symmetric,which results in strong upper-level convergence near the center and hence strong forced subsidence and a very warm core.On the other hand,horizontal advection of temperature cancels part of the adiabatic heating and results in less warming of the core,and hence the TC is not as intense.This advective process is due to the tilt of the vortex as a result of the β-effect.A similar situation occurs in the presence of a uniform flow.Thus,the asymmetric horizontal advection of temperature plays an important role in the temperature distribution.Dynamically,the asymmetric angular momentum (AM) flux is very small on an f-plane throughout the troposphere.However,the total AM exports at the upper levels for a TC either on aβ-plane or with a uniform flow environment are larger because of an increase of the asymmetric as well as symmetric AM export on the plane at radii ＞450 km,and hence there is a lesser intensification.     

Progress in Studies of the Precipitation Diurnal Variation over Contiguous China

This paper summarizes the recent progress in studies of the diurnal variation of precipitation over con- tiguous China. The main results are as follows. （1） The rainfall diurnal variation over contiguous China presents distinct regional features. In summer, precipitation peaks in the late afternoon over the south- ern inland China and northeastern China, while it peaks around midnight over southwestern China. In the upper and middle reaches of Yangtze River valley, precipitation occurs mostly in the early morning. Summer precipitation over the central eastern China （most regions of the Tibetan Plateau） has two diurnal peaks, i.e., one in the early morning （midnight） and the other in the late afternoon. （2） The rainfall diurnal variation experiences obvious seasonal and sub-seasonal evolutions. In cold seasons, the regional contrast of rainfall diurnal peaks decreases, with an early morning maximum over most of the southern China. Over the central eastern China, diurnal monsoon rainfall shows sub-seasonal variations with the movement of summer monsoon systems. The rainfall peak mainly occurs in the early morning （late afternoon） during the active （break） monsoon period. （3） Cloud properties and occurrence time of rainfall diurnal peaks are different for long- and short-duration rainfall events. Long-duration rainfall events are dominated by strat- iform precipitation, with the maximum surface rain rate and the highest profile occurring in the late night to early morning, while short-duration rainfall events are more related to convective precipitation, with the maximum surface rain rate and the highest profile occurring between the late afternoon and early night. （4） The rainfall diurnal variation is influenced by multi-scale mountain-valley and land-sea breezes as well as large-scale atmospheric circulation, and involves complicated formation and evolution of cloud and rainfall systems. The diurnal cycle of winds in the lower troposphere also contributes to the regional differences     

TRMM-Observed Summer Warm Rain over the Tropical and Subtropical Pacific Ocean:Characteristics and Regional Differences

Based on the merged measurements from the TRMM Precipitation Radar and Visible and Infrared Scanner,refined characteristics(intensity,frequency,vertical structure,and diurnal variation) and regional differences of the warm rain over the tropical and subtropical Pacific Ocean(40°S-40°N,120°E-70°W)in boreal summer are investigated for the period 1998-2012.The results reveal that three warm rain types(phased,pure,and mixed) exist over these regions.The phased warm rain,which occurs during the developing or declining stage of precipitation weather systems,is located over the central to western Intertropical Convergence Zone,South Pacific Convergence Zone,and Northwest Pacific.Its occurrence frequency peaks at midnight and minimizes during daytime with a 5.5-km maximum echo top.The frequency of this warm rain type is about 2.2%,and it contributes to 40%of the regional total rainfall.The pure warm rain is characterized by typical stable precipitation with an echo top lower than 4 km,and mostly occurs in Southeast Pacific.Although its frequency is less than 1.3%,this type of warm rain accounts for 95%of the regional total rainfall.Its occurrence peaks before dawn and it usually disappears in the afternoon.For the mixed warm rain,some may develop into deep convective precipitation,while most are similar to those of the pure type.The mixed warm rain is mainly located over the ocean east of Hawaii.Its frequency is 1.2%,but this type of warm rain could contribute to 80%of the regional total rainfall.The results also uncover that the mixed and pure types occur over the regions where SST ranges from 295 to 299 K,accompanied by relatively strong downdrafts at 500 hPa.Both the mixed and pure warm rains happen in a more unstable atmosphere,compared with the phased warm rain.     

Diurnal cycles of precipitation over subtropical China in IPCC AR5 AMIP simulations

Atmospheric Intercomparison Project simulations of the summertime diurnal cycle of precipitation and low-level winds over subtropical China by Intergovernmental Panel on Climate Change Fifth Assessment Report models were evaluated. By analyzing the diurnal variation of convective and stratiform components, results confirmed that major biases in rainfall diurnal cycles over subtropical China are due to convection parameterization and further pointed to the diurnal variation of convective rainfall being closely related to the closure of the convective scheme. All models captured the early-morning peak of total rainfall over the East China Sea, but most models had problems in simulating diurnal rainfall variations over land areas of subtropical China. When total rainfall was divided into stratiform and convective rainfall, all models successfully simulated the diurnal variation of stratiform rainfall with a maximum in the early morning. The models, overestimating noon-time （nocturnal） total rainfall over land, generally simulated too much convective rainfall, which peaked close to noon （midnight）, sharing some similarities in the closures of their deep convection schemes. The better performance of the Meteorological Research Institute atmospherer. ocean coupled global climate model version 3 （MRI-CGCM3） is attributed to the well captured ratio of the two kinds of rainfall, but not diurnal variations of the two components. Therefore, a proper ratio of convective and stratiform rainfall to total rainfall is also important to improve simulated diurnal rainfall variation.