Seasonal evolution of the dominant modes of the Eurasian snowpack and atmospheric circulation from autumn to the subsequent spring and the associated surface heat budget

This study investigates the seasonal evolution of the dominant modes of the Eurasian snowpack and atmospheric circulation from autumn to the subsequent spring using snow water equivalent （SWE）, snow cover frequency （SCF）, and 500 hPa geopotential height data. It is found that the Eurasian SWE/SCF and circulation dominant modes are stably coupled from autumn to the subsequent spring.The temporal coherence of the seasonal evolution of the dominant modes is examined.The seasonal evolution of the Eurasian circulation and SWE dominant modes exhibit good coherence, whereas the evolution of the Eurasian SCF dominant mode is incoherent during the autumn-winter transition season. This incoherence is associated with a sign-change in the SCF anomalies in Europe during the autumn-winter transition season, which is related to the wind anomalies over Europe. In addition, the surface heat budget associated with the Eurasian SWE/SCF and circulation dominant modes is analyzed. The sensible heat flux （SHF） related to the wind-induced thermal advection dominates the surface heat budget from autumn to the subsequent spring, with the largest effect during winter. The surface net shortwave radiation is mainly modulated by snow cover rather than cloud cover, which is estimated to be as important as, or likely superior to, the SHF for the surface heat budget during spring.The NCEP-NCAR surface heat flux reanalysis data demonstrate a consistency with the SWE/SCF and air temperature observational data, indicating a good capability for snow-atmosphere interaction analysis.

SIMULATION OF SUMMER CLIMATE IN CHINA DURING 1997 AND 1998 USING A REGIONAL AIR-SEA COUPLED MODEL

Using the regional air-sea coupled climate model RegCM3-POM,a series of numerical experiments are performed to simulate the summer climate in 1997 and 1998 with different coupling time steps.The results show that the coupled model has good performance on the simulation of the summer sea surface temperature(SST) in 1997 and 1998,and the simulation results of CPL1(with the coupling time step at 1 hour) are similar to those of CPL6(with the coupling time step at 6 hours).The coupled model can well simulate SST differences between 1997 and 1998.As for the simulation of the drought in 1997 and the flood in 1998,the results of CPL6 are more accurate.The coupled model can well simulate the drought in 1997 over North China,and compared with the results of the atmosphere model RegCM3,the simulation ability of the coupled model is improved.The coupling model has better ability in the simulation of the circulation in the middle and low levels,and the water vapor transportation in the coupling model is reasonable in both 1997 and 1998.RegCM3(an uncoupled model) cannot correctly simulate the transportation path differences between 1997 and 1998,but the coupled model can simulate the differences well.

Evaluation of the individual allocation scheme and its impacts in a dynamic global vegetation model

The strategies of plant growth play an important role not only in ecosystem structure,but also in global carbon and water cycles.In this work,the individual carbon allocation scheme of tree PFTs and its impacts were evaluated in China with Institute of Atmospheric Physics-Dynamic Global Vegetation Model,version 1.0（IAP-DGVM1.0）as a test-bed.The results showed that,as individual growth,the current scheme tended to allocate an increasing proportion of annual net primary productivity（NPP）to sapwood and decreasing proportions to leaf and root accordingly,which led to underestimated individual leaf biomass and overestimated individual stem biomass.Such biases resulted in an overestimation of total ecosystem biomass and recovery time of mature forests,and an underestimation of ecosystem NPP and tree leaf area index in China.

Energetic processes regulating the strength of MJO circulation over the Maritime Continent during two types of El Ni?o

The zonal shift of SST warming patterns associated with the eastern Pacific （EP） and central Pacific （CP） El Ni（n）o leads to a significant contrast in MJO strength over the Maritime Continent.The MJO circulation tends to be stronger over the Maritime Continent during the mature phase （autumnwinter） of CP El Ni（n）o than of EP El Ni（n）o.Based on a new MJO kinetic energy （KE） budget equation,in which the effects of mean flow and high-frequency disturbances on the MJO are separated,we found that the low-level MJO gains more KE from the background mean flow during CP El Ni（n）o events,although at the same time the enhanced MJO transfers more KE to high-frequency eddies.Among the three-dimensional circulation anomalies,the low-level convergence and cyclonic anomalies associated with upward anomalies of the Walker circulation over the Maritime Continent play leading roles in inducing the enhanced barotropic energy conversion from mean flow to MJO during CP El Ni（n）o events relative to EP El Ni（n）o events.The more vigorous MJO with strengthened vertical motion and heating anomalies at the upper troposphere can maintain its amplitude through the baroclinic energy conversion from the MJO available potential energy to KE.Both the low-tomid tropospheric barotropic energy conversion from mean flow to MJO and upper-level baroclinic energy conversion contribute positively to the enhanced MJO over the Maritime Continent during CP El Ni（n）o years compared to during EP El Ni（n）o years.

Response of fine particulate matter to reductions in anthropogenic emissions in Beijing during the 2014 Asia–Pacific Economic Cooperation summit

The nested-grid capability of the global chemical transport model GEOS-Chem, with a horizontal resolution of 1/4°× 5/16° （latitude x longitude）, was used to identify the chemical species whose reductions made the largest contributions to decreases in PM2.s concentrations （fine particulate matter, diameter 〈 2.5μm, defined in this study as the sum of sulfate, nitrate, ammonium, black carbon, and organic carbon aerosols） in Beijing during the 2014 Asia-Pacific Economic Cooperation （APEC） summit. A number of numerical experiments were carried out for the period 15 October-29 November 2014. The model reproduced the observed daily variations of concentrations of PM2.s and gas-phase species （carbon monoxide, nitrogen dioxide, and sulfur dioxide）. Simulated PM2.s concentrations decreased by 55.9%-58.5% during the APEC period, compared to other periods in October and November 2014, which agreed closely with measurements. Sensitivity results showed that emissions control measures regarding nitrogen oxides and organic carbon over North China led to the largest reductions in PM2.s concentrations in Beijing during the APEC summit, which led to overall reductions in the PM2.5 concentration of Beijing by 5.7% and 4.6%, respectively. The control of ammonia emissions was found to be able to greatly reduce PM2.5 concentrations in the whole of North China during the APEC meeting.

Crystal Structure and Theoretical Energy Gap of 2-(2-((4-(Pyridin-2-yl)pyrimidin-2-yl)disulfanyl)pyrimidin-4-yl)pyridinium Hexafluorophosphate

The crystal structure of 2-（2-（（4-（pyridin-2-yl）pyrimidin-2-yl）disulfanyl）pyrimidin-4-yl）pyridinium hexafluorophosphate was obtained by X-ray single-crystal diffraction. This molecule crystallizes in monoclinic P2/c space group with a=6.219（1）, b=13.103（2）, c=13.059（2） , β=97.567（2）°, Z=2, the final R=0.0525 and w R=0.1434. The title compound was prepared successfully from 1,2-bis（4-（pyridin-3-yl）pyrimidin-2-yl）disulfane（BPPD）. TD-DFT computational studies on energy gaps and UV-Vis spectra of BPPD and the title compound have been carried out for comparisons. The resultant HOMO-LUMO gap of the BPPD compound is 4.45 e V, while that for the corresponding hexafluorophosphate salt is much smaller at 2.46 e V, which are in agreement with their UV-Vis absorptions.

A synthetic aperture radar sea surface distribution estimation by n-order Bézier curve and its application in ship detection

To dates,most ship detection approaches for single-pol synthetic aperture radar（SAR） imagery try to ensure a constant false-alarm rate（CFAR）.A high performance ship detector relies on two key components：an accurate estimation to a sea surface distribution and a fine designed CFAR algorithm.First,a novel nonparametric sea surface distribution estimation method is developed based on n-order Bézier curve.To estimate the sea surface distribution using n-order Bézier curve,an explicit analytical solution is derived based on a least square optimization,and the optimal selection also is presented to two essential parameters,the order n of Bézier curve and the number m of sample points.Next,to validate the ship detection performance of the estimated sea surface distribution,the estimated sea surface distribution by n-order Bézier curve is combined with a cell averaging CFAR（CA-CFAR）.To eliminate the possible interfering ship targets in background window,an improved automatic censoring method is applied.Comprehensive experiments prove that in terms of sea surface estimation performance,the proposed method is as good as a traditional nonparametric Parzen window kernel method,and in most cases,outperforms two widely used parametric methods,K and G0 models.In terms of computation speed,a major advantage of the proposed estimation method is the time consuming only depended on the number m of sample points while independent of imagery size,which makes it can achieve a significant speed improvement to the Parzen window kernel method,and in some cases,it is even faster than two parametric methods.In terms of ship detection performance,the experiments show that the ship detector which constructed by the proposed sea surface distribution model and the given CA-CFAR algorithm has wide adaptability to different SAR sensors,resolutions and sea surface homogeneities and obtains a leading performance on the test dataset.

Observed Trends in Various Aspects of Compound Heat Waves across China from 1961 to 2015

Based on combined thresholds of daily maximum and minimum temperatures, a compound heat wave is defined, and then changes in multiple aspects of such heat waves in China are estimated between 1961 and 2015. Our results intriguingly indicate that severe compound heat waves in northern China are characterized by excessively high in- tensity within short duration, while long duration determines great disaster-causing potential of severe events in the south. In the past few decades, large areas of China have experienced longer, stronger, and more frequent compound heat waves. Northern China has witnessed dramatic intensity increases, with a maximum amplification over 5~C dec- ade-~; while remarkable lengthening in duration has been mostly recorded in the south, with a maximum trend over 1 day decade-1. The spatial extent affected by compound heat waves has significantly expanded since the 1960s, with the largest expanding rate over 6% decade-1 detected in North China and Northeast China. These systematic assess- ments serve to deepen our understanding of observed changes in compound heat waves across China, and may fur- ther shed some light on future adaptations and mitigations against an increasingly wanning climate.

Assessment of the GPM and TRMM Precipitation Products Using the Rain Gauge Network over the Tibetan Plateau

Using high-quality hourly observations from national-level ground-based stations, the satellite-based rainfall products from both the Global Precipitation Measurement（GPM） Integrated Multisatellit E Retrievals for GPM（IMERG） and its predecessor, the Tropical Rainfall Measuring Mission（TRMM） Multi-satellite Precipitation Analysis（TMPA）, are statistically evaluated over the Tibetan Plateau（TP）, with an emphasis on the diurnal variation.The results indicate that：（1） the half-hourly IMERG rainfall product can explicitly describe the diurnal variation over the TP, but with discrepancies in the timing of the greatest precipitation intensity and an overestimation of the maximum rainfall intensity over the whole TP. In addition, the performance of IMERG on the hourly timescale, in terms of the correlation coefficient and relative bias, is different for regions with sea level height below or above 3500 m;（2） the IMERG products, having higher correlation and lower root-mean-square error, perform better than the TMPA products on the daily and monthly timescales; and（3） the detection ability of IMERG is superior to that of TMPA, as corroborated by a higher Hanssen and Kuipers score, a higher probability of detection, a lower false alarm ratio, and a lower bias. Compared to TMPA, the IMERG products ameliorate the overestimation across the TP. In conclusion,GPM IMERG is superior to TRMM TMPA over the TP on multiple timescales.

Improving CLM4.5 Simulations of Land–Atmosphere Exchange during Freeze–Thaw Processes on the Tibetan Plateau

Soil is heterogeneous and has different thermal and hydraulic properties, causing varied behavior in heat and mois- ture transport. Therefore, soil has an important effect on lanatmosphere interactions. In this study, an improved soil parameterization scheme that considers gravel and organic matter in the soil was introduced into CLM4.5 （Com- munity Land Model）. By using data from the Zoige and Madoi sites on the Tibetan Plateau, the ability of the model to simultaneously simulate the duration of freeze-thaw periods, soil temperature, soil moisture, and surface energy during freeze-thaw processes, was validated. The results indicated that： （1） the new parameterization performed bet- ter in simulating the duration of the frozen, thawing, unfrozen, and freezing periods; （2） with the new scheme, the soil thermal conductivity values were decreased; （3） the new parameterization improved soil temperature simulation and effectively decreased cold biases; （4） the new parameterization scheme effectively decreased the dry biases of soil li- quid water content during the freezing, completely frozen, and thawing periods, but increased the wet biases during the completely thawed period; and （5） the net radiation, latent heat flux, and soil surface heat flux of the Zoige and Madoi sites were much improved by the new organic matter and thermal conductivity parameterization.

Remote Sensing of Tropical Cyclone Thermal Structure from Satellite Microwave Sounding Instruments: Impacts of Background Profiles on Retrievals

A variational retrieval system often requires background atmospheric profiles and surface parameters in its minimization process. This study investigates the impacts of specific background profiles on retrievals of tropical cyclone(TC) thermal structure. In our Microwave Retrieval Testbed(MRT), the K-means clustering algorithm is utilized to generate a set of mean temperature and water vapor profiles according to stratiform and convective precipitation in hurricane conditions. The Advanced Technology Microwave Sounder(ATMS) observations are then used to select the profiles according to cloud type. It is shown that the cloud-based background profiles result in better hurricane thermal structures retrieved from ATMS observations. Compared to the Global Positioning System(GPS) dropsonde observations, the temperature and specific humidity errors in the TC inner region are less than 3 K and 2.5 g kg^(–1), respectively, which are significantly smaller than the retrievals without using the cloud-based profiles. Further experiments show that all the ATMS observations could retrieve well both temperature and humidity structures, especially within the inner core region. Thus, both temperature and humidity profiles derived from microwave sounding instruments in hurricane conditions can be reliably used for evaluation of the storm intensity with a high fidelity.

Estimation and inter-comparison of dust aerosols based on MODIS, MISR and AERONET retrievals over Asian desert regions

This study presents detailed analysis of spatiotemporal variations and trend of dust optical properties i.e., Aerosol Optical Depth(AOD) and Angstrom component over Asian desert regions using thirteen years of data(i.e., 2001–2013) retrieved from Aerosol Robotic Network(AERONET), Moderate Resolution Imaging Spectroradiometer(MODIS) and Multi-angle Imaging Spectroradiometer(MISR). These regions include Solar Village, Dunhuang and Dalangzadgad and are considered as origin of desert aerosols in Asia. Mann–Kendall trend test was used to show the trend of AOD. The relationship of AOD with weather parameters and general AOD trend over different wavelengths has also been shown. AOD's trend has been observed significant throughout the year in Solar Village, while in Dunhuang and Dalanzadgad the significant trend has been found only in peak period(March–June).Analysis show high values of AOD and low values of angstrom in Solar Village during peak period. In Chinese desert regions, high values of AOD have been found during peak period and low values in pre-peak period. Significant relationship has been observed between AOD and average temperature in Solar Village and Dalanzadgad whereas rainfall and wind speed showed no significant impact on AOD in all desert regions.

Joint Impacts of SSTA in Tropical Pacific and Indian Oceans on Variations of the WPSH

Using the NCEP/NCAR reanalysis and HadlSST sea surface temperature （SST） data, the joint effects of the tropi-cal Indian Ocean and Pacific on variations of area of the summertime western Pacific subtropical high （WPSH） for period 1980-2016 are investigated. It is demonstrated that the central tropical Indian Ocean （CTI） and central equat-orial Pacific （CEP） are two key oceanic regions that affect the summertime WPSH. During autumn and winter, warm SST anomalies （SSTAs） in CEP force the Walker circulation to change anomalously, resulting in divergence anom- alies over the western Pacific and Maritime Continent （MC）. Due to the Gill-type response, the abnormal anticyclo- nic circulation is generated over the western Pacific and South China Sea （SCS）. In the subsequent spring, the warm SSTAs in CEP weaken, while the SST over CTI demonstrates a lagged response to Pacific SSTA. The warm CTI-SSTA and CEP-SSTA cooperate with the eastward propagation of cold Kelvin waves in the western Pacific, leading to the eastward shift of the abnormal divergence center that originally locates at the western Pacific and MC. The an-ticyclone forced by this divergence subsequently moves eastward, leading to the intensification of the negative vorti- city there. Meanwhile, warm SSTA in CTI triggers eastward propagating Kelvin waves, which lead to easterly anom- alies over the equatorial Indian Ocean and Indonesia, being favorable for maintenance and intensification of the anti-cyclone over the SCS and western Pacific. The monsoonal meridional-vertical circulation strengthens, which is fa-vorable for the intensification of the WPSH. Using SSTA over the two key oceanic regions as predictors, a multiple regression model is successfully constructed for prediction of WPSH area. These results are useful for our better un-derstanding the variation mechanisms of WPSH and better predicting summer climate in East Asia.

Liquid Water Path Retrieval Using the Lowest Frequency Channels of Fengyun-3C Microwave Radiation Imager(MWRI)

The Microwave Radiation Imager （MWRI） on board Chinese Fengyun-3 （FY-3） satellites provides measurements at 10.65, 18.7, 23.8, 36.5, and 89.0 GHz with both horizontal and vertical polarization channels. Brightness temperature measurements of those channels with their central frequencies higher than 19 GHz from satellite-based microwave imager radiometers had traditionally been used to retrieve cloud liquid water path （LWP） over ocean. The results show that the lowest frequency channels are the most appropriate for retrieving LWP when its values are large. Therefore, a modified LWP retrieval algorithm is developed for retrieving LWP of different magnitudes involving not only the high frequency channels but also the lowest frequency channels of FY-3 MWRI. The theoretical estimates of the LWP retrieval errors are between 0.11 and 0.06 mm for 10.65- and 18.7-GHz channels and between 0.02 and 0.04 mm for 36.5- and 89.0-GHz channels. It is also shown that the brightness temperature observations at 10.65 GHz can be utilized to better retrieve the LWP greater than 3 mm in the eyewall region of Super Typhoon Neoguri （2014）. The spiral structure of clouds within and around Typhoon Neoguri can be well captured by combining the LWP retrievals from different frequency channels.

Simulation of the stratosphere-troposphere exchange process in a typical cold vortex over Northeast China

A mesoscale weather research and forecasting(WRF)model was used to simulate a cold vortex that developed over Northeast China during June 19–23,2010.The simulation used high vertical resolution to reproduce the key features of the cold vortex development.Characteristics of the associated stratosphere-troposphere exchange(STE),specifically the spatiotemporal distribution of the cross-tropopause mass flux(CTF),were investigated using the Wei formula.The simulation results showed that the net mass exchange induced by the cold vortex was controlled by stratosphere-to-troposphere transport(STT)processes.In the pre-formation stage of the cold vortex(i.e.,the development of the trough and ridge),active exchange was evident.Over the lifecycle of the cold vortex,STT processes prevailed at the rear of the trough and moving vortex,whereas troposphere-to-stratosphere transport(TST)processes prevailed at the front end.This spatial pattern was caused by temporal fluctuations of the tropopause.However,because of the cancellation of the upward flux by the downward flux,the contribution of the tropopause fluctuation term to the net mass exchange was only minor.In this case,horizontal motion dominated the net mass exchange.The time evolution of the CTF exhibited three characteristics:(1)the predominance of the STT during the pre-formation stage;(2)the formation and development of the cold vortex,in which the CTF varied in a fluctuating pattern from TST to STT to TST;and(3)the prevalence of the STT during the decay stage.

Analysis of the Structure of Different Tibetan Plateau Vortex Types

Knowledge of the structure of the Tibetan Plateau vortex （TPV） is of considerable importance for understanding the generation and development mechanisms of this mesoscale system. However, our understanding of vortex struc- tures and our ability to classify them on a physical basis is limited due to insufficient observations. The high- resolution new-generation NCEP-CFSR （Climate Forecast System Reanalysis） dataset is used in the present paper to investigate the general structural features of various types of mature TPV through classification and composite struc- ture analysis. Results indicate that the dynamic and thermodynamic structures show regional and seasonal depend- ency, as well as being influenced by attributes of translation, associated precipitation, and the South Asian high （SAH）. The common precipitating TPV （type I）, frequently occurring in the west-east-oriented zonal region between 33° and 36°N, is a notably low-level baroclinic and asymmetric system. It resides within a large-scale confluent zone and preferentially travels eastward, potentially moving out of the plateau. The heavy rain vortex （type II） corresponds to a deep vortex circulation occurring in midsummer. The low-level baroclinic sub-category （type IIa） is associated with a low-level jet and mainly originates in the area 32°-35°N, 86°-94°E, preferentially moving east of 90°E and even away from the plateau; meanwhile, the nearly upright sub-category （type IIb）, which has a cold center at low levels and a warm center at mid-upper levels, is a quasi-stationary and quasi-symmetric system favorably occurring west of 92°E. A western-pattern SAH exists in the upper troposphere for these two sub-categories. The springtime dry vortex in the western plateau （type III） is warm and shallow （approximately 100 hPa deep）, and zonal circulation dominates the large-scale environmental flows in the middle and upper troposphere. The precipitating vortex in the southern plateau occurring during July-August （type IV） is not affected by northerly flow at low levels. It is vertically aligned and controlled by a banded SAH.

An Assessment of ENSO Stability in CAMS Climate System Model Simulations

We present an overview of the El Ni?o–Southern Oscillation(ENSO) stability simulation using the Chinese Academy of Meteorological Sciences climate system model(CAMS-CSM). The ENSO stability was quantified based on the Bjerknes(BJ) stability index. Generally speaking, CAMS-CSM has the capacity of reasonably representing the BJ index and ENSO-related air–sea feedback processes. The major simulation biases exist in the underestimated thermodynamic damping and thermocline feedbacks. Further diagnostic analysis reveals that the underestimated thermodynamic feedback is due to the underestimation of the shortwave radiation feedback, which arises from the cold bias in mean sea surface temperature(SST) over central–eastern equatorial Pacific(CEEP). The underestimated thermocline feedback is attributed to the weakened mean upwelling and weakened wind–SST feedback(μ_a) in the model simulation compared to observation. We found that the weakened μ_a is also due to the cold mean SST over the CEEP.The study highlights the essential role of reasonably representing the climatological mean state in ENSO simulations.

Interannual Variability of Summertime Outgoing Longwave Radiation over the Maritime Continent in Relation to East Asian Summer Monsoon Anomalies

The Maritime Continent（MC） is under influences of both the tropical Pacific and the Indian Ocean. Anomalous convective activities over the MC have significant impacts on the East Asian summer monsoon（EASM） and climate in China. In the present study, the variation in convective activity over the MC in boreal summer and its relationship to EASM anomalies are investigated based on regression analysis of NCEP–NCAR reanalysis and CMAP [Climate Prediction Center（CPC） Merged Analysis of Precipitation] data, with a focus on the impacts of ENSO and the Indian Ocean Dipole（IOD）. The most significant interannual variability of convective activity is found over 10°S–10°N, 95°–145°E, which can be roughly defined as the key area of the MC（hereafter, KMC）. Outgoing longwave radiation anomaly（OLRA） exhibits 3- to 7-yr periodicities over the KMC, and around 70% of the OLRA variance can be explained by the ENSO signal. However, distinct convection and precipitation anomalies still exist over this region after the ENSO and IOD signals are removed. Abnormally low precipitation always corresponds to positive OLRA over the KMC when negative diabatic heating anomalies and anomalous cooling of the atmospheric column lead to abnormal descending motion over this region. Correspondingly, abnormal divergence occurs in the lower troposphere while convergence occurs in the upper troposphere, triggering an East Asia–Pacific/Pacific–Japan（EAP/PJ）-like anomalous wave train that propagates northeastward and leads to a significant positive precipitation anomaly from the Yangtze River valley in China to the islands of Japan. This EAP/PJ-like wave pattern becomes even clearer after the removal of the ENSO signal and the combined effects of ENSO and IOD, suggesting that convective anomalies over the KMC have an important impact on EASM anomalies. The above results provide important clues for the prediction of EASM anomalies and associated summer precipitation anomalies in China.

Detecting Primary Precursors of January Surface Air Temperature Anomalies in China

This study aims to detect the primary precursors and impact mechanisms for January surface temperature anomaly （JSTA） events in China against the background of global warming, by comparing the causes of two extreme JSTA events occurring in 2008 and 2011 with the common mechanisms inferred from all typical episodes during 1979- 2008. The results show that these two extreme events exhibit atmospheric circulation patterns in the mid-high latitudes of Eurasia, with a positive anomaly center over the Ural Mountains and a negative one to the south of Lake Baikal （UMLB）, which is a pattern quite similar to that for all the typical events. However, the Eurasian teleconnection patterns in the 2011 event, which are accompanied by a negative phase of the North Atlantic Oscillation, are different to those of the typical events and the 2008 event. We further find that a common anomalous signal appearing in early summer over the tropical Indian Ocean may be responsible for the following late-winter Eurasian teleeonnec- lions and the associated JSTA events in China. We show that sea surface temperature anomalies （SSTAs） in the preceding summer over the western Indian Ocean （WIO） are intimately related to the UMLB-like circulation pattern in the following January. Positive WIOSSTAs in early summer tend to induce strong UMLB-like circulation anomalies in January, which may result in anomalously or extremely cold events in China, which can also be successfully reproduced in model experiments. Our results suggest that the WIOSSTAs may be a useful precursor for predicting JSTA events in China.

Characteristics and Possible Formation Mechanisms of Severe Storms in the Outer Rainbands of Typhoon Mujigae(1522)

To better understand how severe storms form and evolve in the outer rainbands of typhoons, in this study, we in- vestigate the evolutionary characteristics and possible formation mechanisms for severe storms in the rainbands of Typhoon Mujigae, which occurred during 2-5 October 2015, based on the NCEP-NCAR reanalysis data, conventional observations, and Doppler radar data. For the rainbands far from the inner core （eye and eyewall） of Mujigae （dis- tance of approximately 70-800 kin）, wind speed first increased with the radius expanding from the inner core, and then decreased as the radius continued to expand. The Rankine Vortex Model was used to explore such variations in wind speed. The areas of strong stormy rainbands were mainly located in the northeast quadrant of Mujigae, and overlapped with the areas of high winds within approximately 300-550 km away from the inner core, where the strong winds were conducive to the development of strong storms. A severe convective cell in the rainbands de- veloped into waterspout at approximately 500 km to the northeast of the inner core, when Mujigae was strengthening before it made landfall. Two severe convective cells in the rainbands developed into two tornadoes at approximately 350 km to the northeast of the inner core after Mujigae made landfall. The radar echo bands enhanced to 60 dBZ when mesocyclones occurred in the rainbands and induced tornadoes. The radar echoes gradually weakened after the mesocyclones weakened. The tops of parent clouds of the mesocyclones elevated at first, and then suddenly dropped about 20 min before the tornadoes appeared. Thereby, the cloud top variation has the potential to be used as an early warning of tornado occurrence.