The Relationships between Variations of Sea Surface Temperature Anomalies in the Key Ocean Areas and the Precipitation and Surface Air Temperature in China

The relationships between variations of sea surface temperature anomalies (SSTVA) in the key ocean areas and the precipitation / temperature anomalies in China are studied based on the monthly mean sea surface temperature data from January 1951 to December 1998 and the same stage monthly mean precipitation/ temperature data of 160 stations in China. The purpose of the present study is to discuss whether the relationship between SSTVA and precipitation / temperature is different from that between sea surface temperature anomalies (SSTA) and precipitation/ temperature, and whether the uncertainty of prediction can be reduced by use of SSTVA. The results show that the responses of precipitation anomalies to the two kinds of tendency of SSTA are different. This implies that discussing the effects of two kinds of tendency of SSTA on precipitation anomalies is better than just discussing the effects of SSTA on precipitation anomalies. It helps to reduce the uncertainty of prediction. The temperature anomalies have more identical re-sponses to the two kinds of tendency of SSTA than the precipitation except in the western Pacific Ocean. The response of precipitation anomalies to SSTVA is different from that to SSTA, but there are some similarities. Key words Variations of sea surface temperature anomalies - Precipitation anomalies - Temperature anomalies - Statistical significance test Sponsored jointly by the “ National Key Developing Program for Basic Sciences” (G1998040900) Part I and the Key Program of National Nature Science Foundation of China “ Analyses and Mechanism Study of the Regional Climatic Change in China” under Grant No.49735170.

Trends of Temperature Extremes in China and their Relationship with Global Temperature Anomalies

Changes of temperature extremes over China were evaluated using daily maximum and minimum temperature data from 591 stations for the period 1961-2002. A set of indices of warm extremes, cold extremes and daily temperature range （DTR） extremes was studied with a focus on trends. The results showed that the frequency of warm extremes （F WE） increased obviously in most parts of China, and the intensity of warm extremes （I WE） increased significantly in northern China. The opposite distribution was found in the frequency and intensity of cold extremes. The frequency of high DTR extremes was relatively uniform with that of intensity： an obvious increasing trend was located over western China and the east coast, while significant decreases occurred in central, southeastern and northeastern China; the opposite distribution was found for low DTR extreme days. Seasonal trends illustrated that both F WE and I WE showed signifi- cant increasing trends, especially over northeastern China and along the Yangtze Valley basin in spring and winter. A correlation technique was used to link extreme temperature anomalies over China with global temperature anomalies. Three key regions were identified, as follows： northeastern China and its coastal areas, the high-latitude regions above 40~0N, and southwestern China and the equatorial eastern Pacific.

The Vertical Structures of Atmospheric Temperature Anomalies Associated with El Nio Simulated by the LASG/IAPAGCM: Sensitivity to Convection Schemes

The vertical structures of atmospheric temperature anomalies associated with El Nio are simulated with a spectrum atmospheric general circulation model developed by LASG/IAP （SAMIL）. Sensitivity of the model’s response to convection scheme is discussed. Two convection schemes, i.e., the revised Zhang and Macfarlane （RZM） and Tiedtke （TDK） convection schemes, are employed in two sets of AMIP-type （Atmospheric Model Intercomparison Project） SAMIL simulations, respectively. Despite some deficiencies in the upper troposphere, the canonical El Nio-related temperature anomalies characterized by a prevailing warming throughout the tropical troposphere are well reproduced in both simulations. The performance of the model in reproducing temperature anomalies in ＂atypical＂ El Nio events is sensitive to the convection scheme. When employing the RZM scheme, the warming center over the central-eastern tropical Pacific and the strong cooling in the western tropical Pacific at sea surface level are underestimated. The quadru-pole temperature anomalies in the middle and upper troposphere are also obscured. The result of employing the TDK scheme resembles the reanalysis and hence shows a better performance. The simulated largescale circulations associated with atypical El Nio events are also sensitive to the convection schemes. When employing the RZM scheme, SAMIL failed in capturing the classical Southern Oscillation pattern. In accordance with the unrealistic anomalous Walker circulation and the upper tropospheric zonal wind changes, the deficiencies of the precipitation simulation are also evident. These results demonstrate the importance of convection schemes in simulating the vertical structure of atmospheric temperature anomalies associated with El Nio and should serve as a useful reference for future improvement of SAMIL.

Characteristics of Tropical Sea Surface Temperature Anomalies and Their Influences on the Onset of South China Sea Summer Monsoon

The characteristics of sea surface temperature anomalies （SSTAs） in the tropical oceans and their influences on the onset of South China Sea summer monsoon （SCSSM） have been studied.The anomaly of SST in tropical Pacific Ocean exerts persistence impact for one to three months on atmospheric circulations.If the warm pool becomes anomalously warmer during an earlier period from February to April,the SCSSM breaks out earlier,and vice versa.Singular value decomposition （SVD） and composite analysis have shown that,in La Ni（n）a pattern,the convection over Western Pacific will occur earlier and be stronger than normal,which favors the convergence at a lower layer over Western Pacific,as well as the strengthening of upwelling branch of Walker circulation,leading to an earlier burst of westerly in the southern South China Sea.Moreover,the convection in Sumatra appears earlier than normal and favors the westerly evolution in eastern Indian Ocean,resulting in the splitting of the subtropical high belt and an early onset of SCSSM.However,the atmospheric circulation anomaly is reversed in El Ni（n）o pattern.

Subsurface temperature anomalies in the North Pacific Ocean associated with the ENSO cycle

Multi-year Simple Ocean Data Assimilation （SODA） and National Centers for Environmental Prediction （NCEP） datasets were used to investigate the leading patterns of subsurface ocean temperature anomalies （SOTA） and the corresponding atmospheric circulation structure in the Pacific Ocean （20°S-60°N）. In this paper, the evolution of North Pacific SOTA associated with El Nifio-southern oscillation （ENSO）, and their relationship with the overlying zonal/meridional atmospheric circulations were elucidated. The results indicate that： （1） there are two dominant modes for the interannual variability of the North Pacific SOTA. The primary mode is the dipole pattern of the central and western North Pacific SOTA associated with the leading mode of ENSO, and the second mode is the zonal pattern related to the second mode of ENSO. These two modes consist of the temporal-spatial variation of the SOTA in the North Pacific. （2） During the developing phase of the El Nifio event, positive （negative） SOTA appears in the western （central） portion of the North Pacific Ocean. During the mature and decaying phase of the E1 Nifio event, the western positive center and the central negative center continue to be maintained and enhanced. Meanwhile, the position of the western positive center slightly changes, and the central negative center moves eastward slowly. After the El Nifio event vanishes, the positive SOTA disappears, and the central negative SOTA becomes weak and remains in the northeastern Pacific Ocean. The results for La Nifia are generally the opposite. （3） During the El Nifio/La Nifia cycle, formation and evolution of the SOTA, with opposite signs in central and western North Pacific Ocean, resulted from vertical movement of the two northern branches of the Hadley Cell with opposite direction, as well as the positive feedback of the air-sea interaction induced by dynamic processes in the mid-latitudes. The former gives rise to the initial SOTA, and the latter intensifies SOTA. Under the forcing of these two processes, SOTA evolution is formed and sustained during the El Nino/La Nina events. Also discussed herein as background for the ENSO cycle are the possible connections among the West Pacific subtropical high, the strength of the Kuroshio near the East China Sea, the Kuroshio meanders south of Japan, the Aleutian Low, and cold advection in the central North Pacific Ocean.

Global Annual Mean Surface Air Temperature Anomalies and Their Link with Indian Summer Monsoon Failures

Analysis of the global mean annual temperature anomalies based on land and marine data for the last 88 years (1901-1988) of this century has been carried out with a view to find any relationship with failures in Indian summer monsoon rainfall. On the climatological scale (i.e. 30 years) it has been noticed that there is an abnormal increase in the frequency of drought years during epochs of global warming and cooling, while it is considerably less when global temperatures are near normal. Results are unchanged even when the data are filtered out for ENSO (El-Nino Southern Oscillation) effect.It has also been noticed that during warm and cold epochs in global temperatures the amount of summer monsoon rainfall decreases as compared to the rainfall during a normal temperature epoch.

Experiments in numerical modelling of the Pacific sea surface temperature anomalies

By using the atmosphere-ocean coupled model (CGCM) which is composed of a 2-level global atmospheric general circulation model and a 4-layer Pacific oceanic general circulation model developed in the Institute of Atmospheric Physics of Chinese Academy of Sciences, and two model climatological fields got from the two independent models' numerical integrations respectively, the Pacific sea surface temperature anomalies (SSTA) from 1988 to 1989 are simulated in this paper with observed atmospheric general circulation data and sea surface temperature fields as initial conditions and monthly coupling scheme. In order to remove systematic biases of the model climatological fields, interaction variables between atmosphere and ocean are also corrected simultaneously. The experiments show that the simulation results can be improved effectively if these interaction variables are corrected in spite of the fact that there always exist systematic biases in independent numerical simulations of atmospheric part and oceanic part within CGCM. The basic characteristics of the observed Pacific SSTA in September and October 1988 have been simulated by using the correction scheme, such as the negative SSTA domain in the whole E-quatorial Pacific east to 150°E and the positive SSTA domain in the Western Pacific, the northern subtropical Pacific and nearly the whole Southern Pacific. Further numerical simulations show that the model can simulate not only the SSTA in the Pacific and its seasonal variations but also its interannual changes (for example, La Nino event in the Equatorial Pacific terminated after May 1989) to a certain degree. Furthermore, some problems existing in experiment processes and what we shoud do in the following stage are also discussed and analysed in this paper.

Forecasts of South China Sea surface temperature anomalies using the Nio indices and dipole mode index as predictors

Based on an empirical orthogonal function （EOF） analysis of the monthly NCEP Optimum Interpolation Sea Surface Temperature （OISST） data in the South China Sea （SCS） after removing the climatological mean and trends of SST, over the period of January 1982 to October 2003, the corresponding TCF correlates best with the Dipole Mode Index （DMI）, Nino1＋2, Nino3.4, Nino3, and Niflo4 indices with time lags of 10, 3, 6, 5, and 6 months, respectively. Thus, a statistical hindcasts in the prediction model are based on a canonical correlation analysis （CCA） model using the above indices as predictors spanning from 1993/1994 to 2003/2004 with a 1-12 month lead time after the canonical variants are calculated, using data from the training periods from January 1982 to December1992. The forecast model is successful and steady when the lead times are 1-12 months. The SCS warm event in 1998 was successfully predicted with lead times from 1-12 months irrespective of the strength or time extent. The prediction ability for SSTA is lower during weak ENSO years, in which other local factors should be also considered as local effects play a relatively important role in these years. We designed the two forecast models： one using both DMI and Nino indices and the other using only Nino indices without DMI, and compared the forecast accuracies of the two cases. The spatial distributions of forecast accuracies show different confidence areas. By turning off the DMI, the forecast accuracy is lower in the coastal areas off the Philippines in the SCS, suggesting some teleconnection may occur with the Indian Ocean in this area. The highest forecast accuracies occur when the forecast interval is five months long without using the DMI, while using both of Nino indices and DMI, the highest accuracies occur when the forecast interval time is eight months, suggesting that the Nino indices dominate the interannual variability of SST anomalies in the SCS. Meanwhile the forecast accuracy is evaluated over an independent test period of more than 11 years （1993/94 to October 2004） by comparing the model performance with a simple prediction strategy involving the persistence of sea surface temperature anomalies over a 1-12 month lead time （the persisted prediction）. Predictions based on the CCA model show a significant improvement over the persisted prediction, especially with an increased lead time （longer than 3 months）. The forecast model performs steadily and the forecast accuracy, i.e., the correlation coefficients between the observed and predicted SSTA in the SCS are about 0.5 in most middle and southern SCS areas, when the thresholds are greater than the 95% confidence level. For all 1 to 12 month lead time forecasts, the root mean square errors have a standard deviation of about 0.2. The seasonal differences in the prediction performance for the 1-12 month lead time are also examined.

Possible Thermal Brightness Temperature Anomalies Associated with the Yutian (China) M_S7.3 Earthquake on February 12,2014

In order to analyze the seismic brightness temperature anomalies associated with the Yutian earthquake which occurred at Yutian County, Xinjiang on February 12,2014, daily brightness temperature data was collected from the China Geostationary Meteorological Satellite FY-2E,for the period from May 1,2012 to April 30,2014 and the geographical extent of 30°- 45°N latitude and 70°- 95°E longitude. The continuous wavelet transform method was used to analyze the relative wavelet power spectrum( RWPS) of brightness temperature data for each pixel. And the RWPS time-spatial evolution within the analysis area was obtained. The results showed that the anomaly started to appear at the vicinity of epicentre since October 2013, and anomalous areas gradually enlarged and stretched towards to Altun fault zone and the eastern part of West Kunlun fault zone. Anomalies began to appear at fault zones at Middle Tianshan Mountains, Southern Tianshan Mountains and the western part of the West Kunlun Mountains area which is located at the western margin of Tarim basin,since November 2013. Then anomalous area further enlarged and gathered along fault zones,and eventually,anomalous belts were developed along fault zones around the Tarim basin. The anomaly area and amplitude reached their maximum in late December 2013 and early January 2014. With the impending earthquake,the anomaly area and amplitude dwindled. Anomalies at the vicinity of epicentre disappeared days before the occurrence of the main shock. However, the anomaly at Altun and Middle Tianshan areas still remained. After the main shock,the anomaly attenuated quickly and the whole anomaly disappeared in late February 2014.

Effects of Sea Surface Temperature Anomalies off the East Coast of Japan on Development of the Okhotsk High

The study examined effects of sea surface temperature anomalies （SSTAs） off the east coast of Japan on the blocking high over the Okhotsk Sea in June by diagnostic analysis and numerical simulation. Firstly, based on 500-hPa geopotential height fields, the Okhotsk high index （OKHI） for June from 1951 to 2000 is calculated and analyzed. The result indicates that the OKHI has obvious inter-annual and inter-decadal vaxiations, and there are 9 yr of high OKHI and 8 yr of low OKHI in 50 yr. Secondly, by using the OKHI, the relationship between the Okhotsk high and the 500-hPa geopotential height anomaly is investigated. The results indicate that the ＂＋-＋＂ pattern of geopotential height anomaly crossing Eurasia in the mid-high latitudes and the ＂＋-＂ pattern of geopotential height anomaly from high to low latitudes over East Asia are in favor of the formation and maintenance of the Okhotsk high. The relationship between the OKHI and the SSTA over the North Pacific is investigated in early summer by using correlation and composite analysis. We found that when the blocking circulation over the Okhotsk Sea occurs, there is an obvious negative SSTA off the east coast of Japan in early summer. We simulated the effects of the negative SSTA of east coast of Japan on the atmospheric circulation anomaly over East Asia through the control and sensitivity experiments using NCAR CAM3 model in order to confirm our analysis results. The simulation shows that the negative SSTA off the east coast of Japan results in the significant positive 40 gpm 500-hPa geopotential height anomaly over the Okhotsk Sea and the negative anomalies off the east coast of Japan which might contribute to the formation and development of the Okhotsk high in June.

NUMERICAL EXPERIMENTS OF THE EFFECTS OF SEA SURFACE TEMPERATURE ANOMALIES OVER THE PACIFIC ON PRECIPITATION IN 1991

A zonal domain,primitive equation model is used in this paper to study the influences of the main sea surface tem- perature anomaly(SSTA)areas over the Pacific on precipitation in 1991.Some numerical experiments are made and the mechanisms of the influences are discussed.The results show that the influences of the SSTA are mainly confined within the tropical and the subtropical regions.The direct effect of the SSTA is to change the exchanges of the sensible heat and the water vapour between the air and the sea,through the consequent changes of temperature and the flow fields and the feedback process of condensation,the SSTA finally affects precipitation.

Analysis of Temperature Variation in Zhangqiu City during the Past 30 Years

[Objective] This study aimed to analyze the characteristics of temperature variation in Zhangqiu City during the past 30 years. [Method] Variation characteristics of average annual maximum temperature, average annual temperature and average annual minimum temperature in Zhangqiu City during the past 30 years were analyzed by using related temperature data during 1981 -2010 collected from National Meteorological Observation Station in Zhangqiu. [Result] Average annual maximum temperature, average annual temperature and average annual minimum temperature in Zhangqiu City showed an upward trend; average annual minimum temperature showed the most significant increasing tendency, with a tendency rate of 1.347 ℃/10 a; followed by average annual temperature; average annual maximum temperature showed the slowest increasing tendency, with a tendency rate of 0.062 ℃/10 a, indicating that the increase of average annual temperature mainly depended on the contribution of average annual minimum temperature. [Conclusion] This study provides reference and scientific basis for climate change monitoring, diagnosis, assessment, forecast and decision-making in Zhangqiu City.

A DIAGNOSTIC ANALYSIS OF AIR TEMPERATURE ANOMALY MODE OVER CHINA IN 2009/2010 WINTER BASED ON GENERALIZED EQUILIBRIUM FEEDBACK ASSESSMENT(GEFA) METHOD

By using the observed monthly mean data over 160 stations of China and NCAR/NCEP reanalysis data, the generalized equilibrium feedback assessment(GEFA) method, combined with the methods of EOF analysis, correlation and composite analysis, is used to explore the influence of different SST modes on a wintertime air temperature pattern in which it is cold in the northeast and warm in the southwest in China. The results show that the 2009/2010 winter air temperature oscillation mode between the northern and southern part of China is closely related to the corresponding sea surface temperature anomalies(SSTA) and its associated atmospheric circulation anomalies. Exhibiting warming in Northeast China and cooling in Southwest China, the mode is significantly forced by the El Nio mode and the North Atlantic SSTA mode, which have three poles. Under the influence of SSTA modes, the surface northerly flow transported cold air to North and Northeast China, resulting in low temperatures in the regions. Meanwhile, the mid-latitude westerlies intensify and the polar cold air stays in high latitudes and cannot affect the Southwest China, resulting in the warming there.

Long Term Temperature Trends at Major, Medium, Small Cities and Hill Stations in India during the Period 1901-2013

Industrialization and urbanization are the most dominant causal factors for long-term changes in surface air temperatures. To examine this fact, the long term changes in the surface-air temperatures have been evaluated by the linear trend for the different periods, i.e. 1901-2013, 1901-1970 and recent period 1971-2013 as rapid industrialization was observed during the recent four decades. In the present study, seasonal and annual mean, maximum and minimum temperature data of 36 stations for the period 1901-2013 have been used. These stations are classified into 4 groups, namely major, medium, small cities and hill stations. During the period 1901-1970, less than 50% stations from each group showed a significant increasing trend in annual mean temperature, whereas in the recent period 1971-2013, more than 80% stations from all the groups except small city group showed a significant increasing trend. The minimum temperature increased faster than that of the maximum temperature over major and medium cities, while maximum temperature increased faster than the minimum temperature over the small cities and hill stations. The annual mean temperature of all the coastal stations showed a significant increasing trend and positive correlation with Precipitable Water Vapour (PWV). The effect of PWV is more pronounced on minimum temperature than that of the maximum.

The Space and Time Features of Global SST Anomalies Studied by Complex Principal Component Analysis

In this paper, the variability characteristics of the global field of sea surface temperature (SST) anomaly are studied by complex principal component (c.p.c.) analysis, whose results are also compared with those of real p.c. analysis. The data consist of 40 years of global SST monthly averages over latitudes from 42 5°S to 67 5°N. In the spatial domain, it is found that the distribution of the first complex loading amplitude is characterized by three areas of large values: the first one in the eastern and central equatorial Pacific Ocean, the second one in the northern tropical Indian Ocean and South China Sea, the third one in the northern Pacific Ocean. As it will be explained, this pattern may be considered as representative of El Nio mode. The first complex loading phase pattern shows a stationary wave in the Pacific (also revealed by real p.c. analysis) superimposed to an oscillating disturbance, propagating from the Pacific to Indian or the opposite way. A subsequent correlation analysis among different spatial points allows revealing disturbances actually propagating westward from the Pacific to the Indian Ocean, which could therefore represent reflected Rossby waves, i.e. the west phase of the signals that propagate disturbances of thermal structure in the tropical Pacific Ocean. In the time domain, a relation between the trend of the first complex principal component and the ENSO cycle is also established.

Two Northward Jumps of the Summertime Western Pacific Subtropical High and Their Associations with the Tropical SST Anomalies

Based on the pentad mean ridgeline index of the western Pacific subtropical high (WPSH), the authors identified the two northward jumps of the WPSH from 1979 to 2008 and revealed their associations with the tropical SST anomalies. The authors show that the northward jumps, especially the second jump, exhibited remarkable interannual variability. In addition, the authors find that the two northward jumps were mutually independent and were influenced by the SST anomalies in the different regions of the tropical Pacific. The first jump was positively correlated with the SST anomalies in the tropical central Pacific from the preceding winter to June. In contrast, the second jump was positively related to ENSO in the preceding winter, but this correlation tended to weaken with the decay of ENSO and disappeared in July. Instead, a positive correlation was found in the Indian Ocean. We therefore suggest that ENSO plays an indirect role in the second jump through the capacitor effect of the Indian Ocean.

The effects of different sea surface temperature distributions over the western Pacific on the summer monsoon properties

A modified and improved primitive equation numerical model with p-sigma incorporated vertical coordinates is used to simulate the effects of different sea surface temperature distributions over the western Pacific on the summer monsoon properties. The different sea surface temperature (SST) distributions are automatically generated in the time integrations by using two different SST models, one of which is called the deep ocean model (DOM) and the other the shallow ocean model (SOM). The SST generated by the DOM has the distribution pattern of the initial SST which is similar to the pattern in the cold water years over the western Pacific, while the SST generated by the SOM has the pattern similar to that in the warm water years. The differences between the experimental results by using DOM and SOM are analyzed in detail. The analyses indicate that the most basic and important characteristics of the summer monsoon climate can be simulated successfully in both experiments, that means the climatic properties in the monsoonal climate regions are mainly determined by the seasonal heating, the contrast between the land and the sea, the topography, and the physical properties of the underlying surfaces. However, the differences between the two experiments tell us that the climatic properties in the summer monsoon regions in the cold water year and the warm water year do differ from each other in details. In the warm water year, the thermal contrast between the land and the sea becomes weaker. Over the warm water area, the upward motions are induced and the dynamical conditions favorable for the convective activities are formed, the Somali low-level cross equatorial current is somewhat weakened, while the cross equatorial currents, east of 90°E, are strongly strengthened, the precipitation amount in the tropical regions largely increases, and the precipitation over the coastal regions increases, too. However the precipitation over the southeast China and its coastal area decreases. The precipitation amount mainly depends on the strength of the convective activity.

Anomalous changes of temperature and ozone QBOs in 2015−2017 from radiosonde observation and MERRA-2 reanalysis

Anomalous changes of zonal wind quasi-biennial oscillation(QBO)in winter 2015−2016 have received close attention.Combining radiosonde and satellite observations and reanalysis data,we investigate anomalous changes in temperature and ozone QBOs from the lower to middle stratosphere.As wind shear direction is reversed due to unexpected changes of zonal wind QBO at about 24−30 km,the shortest cold phase at 21−27 km appears in temperature QBO.This is different from the completely interrupted westward phase in zonal wind QBO,while the longest cold phase above almost 27 km lasts for 2−3 years from 2015 to 2017,owing to the absence of corresponding warm phase.Meridional scale reduction of temperature QBO causes a small temperature anomaly,thus the thermal wind relationship looks seemingly different from that in the other regular QBO cycles.QBO in the ozone mixing ratio anomaly shows a double-peak with inverse phase,and its phase below(above)30 km is in agreement with(opposite to)the phase of temperature QBO because of different control mechanisms of ozone.Following temperature QBO variation,QBO in the ozone mixing ratio anomaly exhibits a less positive phase at 20−30 km in 2016−2017,and a very long positive phase above 30 km from 2015 to 2017.QBO in total column ozone shows a small peak in winter 2016−2017 since ozone is mainly concentrated at 20 to 30 km.Anomalous changes of temperature and ozone QBOs due to unexpected QBO zonal wind variation can be well-explained according to thermal wind balance and thermodynamic balance.

COMPARISONS OF CIRCULATION ANOMALIES BETWEEN THE DAILY PRECIPITATION EXTREME AND NON-EXTREME EVENTS IN THE MIDDLE AND LOWER REACHES OF YANGTZE RIVER IN BOREAL SUMMER

Based on the NCEP/NCAR reanalysis dataset and in situ meteorological observations of daily precipitation in boreal summer from 1979 to 2008, the features of circulation anomalies have been investigated using the composite analysis for the extreme events and non-extreme events of regional mean daily rainfall(RMDR) occurring over the midand lower- Yangtze valley(MLYV). The extreme RMDR(ERMDR) events are the events at and above the percentile99 in the rearranged time-series of the RMDR with ascending order of rainfall amount. The non-extreme RMDR events are those at the percentiles 90-85 and 80-75 separately. Our results suggest that the threshold value is 25 mm/day for the ERMDR at percentile 99. Precipitation at all the percentiles is found to occur more frequently in the Meiyu rainfall season in MLYV, and the ERMDR events have occurred with higher frequency since the 1990 s. For the percentiles-associated events, the MLYV is under the control of an anomalous cyclonic circulation in the mid- and lower- troposphere with vastly different anomalous circulation at higher levels. However, at both low and high levels, the ERMDR events-related anomalous circulation is stronger compared to that linked to the non-ERMDR events. The dominant sources of water vapor differ between the ERMDR and non-ERMDR events. During the ERMDR events plentiful water vapor is transported from the Bay of Bengal into the MLYV directly by divergence while there is distinctly increased water vapor from the South China Sea(SCS) in non-RMERMDR episodes. The diabatic heating rates < Q1>, < Q2> and< Q1>- < Q2> have their anomalous patterns and are consistent with each other for these percentiles but their strength decreases markedly with the drop of rainfall intensity. For the precipitation at percentiles 99 and 90-85, the sea surface temperature anomalies(SSTA) in the Pacific distribute positively(negatively) in the south(north), and are stronger when the ERMDR emerges, with little or no SSTA as the events at percentile 80-75 occur. Besides, these results suggest that the genesis of the ERMDR event is directly related to intense local circulation anomalies and the circulation anomalies over the Pacific and SCS in tropical to mid-latitudes, and probably linked with the Pacific SSTA closely while the non-ERMDR events are mainly associated with the anomalous circulation on a local basis. The findings here help understand and predict the happening of ERMDR events over the MLYV.

Impacts of SST and SST Anomalies on Low-Frequency Oscillation in the Tropical Atmosphere

Considering the multiscale character of LFO effects of SST on LFO in the tropical atmosphere （low-frequency oscillation） in the tropical atmosphere, the are discussed by using an absolute ageostrophic, baroclinic model. Here, SST effects include sea surface heating and forcing of SST anomalies （SSTAs）. Studies of the influences of sea surface heating on LFO frequency and stability show that sea surface heating can slow the speed of waves and lower their frequency when SST is comparatively low; while higher SST leads to unstable waves and less periods of LFO. Since the impact of a SSTA on ultra-long waves is more evident than that on kilometer-scale waves, long-wave approximation is used when we continue to study the effect of SSTAs. Results indicate that SSTAs can lead to a longer period of LFO, and make waves unstable. In other words, positive （negative） SSTAs can make waves decay （grow）.