Wind regime features and their impacts on the middle reaches of the Yarlung Zangbo River on the Tibetan Plateau, China

The wide valley of the Yarlung Zangbo River is one of the most intense areas in terms of aeolian activity on the Tibetan Plateau,China.In the past,the evaluation of the intensity of aeolian activity in the Quxu–Sangri section of the Yarlung Zangbo River Valley was mainly based on data from the old meteorological stations,especially in non-sandy areas.In 2020,six new meteorological stations,which are closest to the new meteorological stations,were built in the wind erosion source regions(i.e.,sandy areas)in the Quxu–Sangri section.In this study,based on mathematical statistics and empirical orthogonal function(EOF)decomposition analysis,we compared the difference of the wind regime between new meteorological stations and old meteorological stations from December 2020 to November 2021,and discussed the reasons for the discrepancy.The results showed that sandy and non-sandy areas differed significantly regarding the mean velocity(8.3(±0.3)versus 7.7(±0.3)m/s,respectively),frequency(12.9%(±6.2%)versus 2.9%(±1.9%),respectively),and dominant direction(nearly east or west versus nearly north or south,respectively)of sand-driving winds,drift potential(168.1(±77.3)versus 24.0(±17.9)VU(where VU is the vector unit),respectively),resultant drift potential(92.3(±78.5)versus 8.7(±9.2)VU,respectively),and resultant drift direction(nearly westward or eastward versus nearly southward or northward,respectively).This indicated an obvious spatial variation in the wind regime between sandy and non-sandy areas and suggested that there exist problems when using wind velocity data from non-sandy areas to evaluate the wind regime in sandy areas.The wind regime between sandy and non-sandy areas differed due to the differences in topography,heat flows,and their coupling with underlying surface,thereby affecting the local atmospheric circulation.Affected by large-scale circulations(westerly jet and Indian monsoon systems),both sandy and non-sandy areas showed similar seasonal variations in their respective wind regime.These findings provide a credible reference for re-understanding the wind regime and scientific wind-sand control in the middle reaches of the Yarlung Zangbo River Valley.

Analysis of the Structure and Propagation of a Simulated Squall Line on 14 June 2009

A squall line on 14 June 2009 in the provinces of Jiangsu and Anhui was well simulated using the Advanced Regional Prediction System （ARPS） model. Based on high resolution spatial and temporal data, a detailed analysis of the structural features and propagation mechanisms of the squall line was conducted. The dynamic and thermodynamic structural charac- teristics and their causes were analyzed in detail. Unbalanced flows were found to play a key role in initiating gravity waves during the squall line＇s development. The spread and development of the gravity waves were sustained by convection in the wave-CISK process. The squall line＇s propagation and development mainly relied on the combined effect of gravity waves at the midlevel and cold outflow along the gust front. New cells were continuously forced by the cold pool outflow and were enhanced and lifted by the intense upward motion. At a particular phase, the new cells merged with the updraft of the gravity waves, leading to an intense updraft that strengthened the squall line.

Analysis of the Characteristics of Inertia-Gravity Waves during an Orographic Precipitation Event

A numerical experiment was performed using the Weather Research and Forecasting（WRF） model to analyze the generation and propagation of inertia-gravity waves during an orographic rainstorm that occurred in the Sichuan area on 17 August 2014. To examine the spatial and temporal structures of the inertia-gravity waves and identify the wave types, three wavenumber-frequency spectral analysis methods（Fourier analysis, cross-spectral analysis, and wavelet cross-spectrum analysis）were applied. During the storm, inertia-gravity waves appeared at heights of 10-14 km, with periods of 80-100 min and wavelengths of 40-50 km. These waves were generated over a mountain and propagated eastward at an average speed of 15-20 m s^（-1）. Meanwhile, comparison between the reconstructed inertia-gravity waves and accumulated precipitation showed there was a mutual promotion process between them. The Richardson number and Scorer parameter were used to demonstrate that the eastward-moving inertia-gravity waves were trapped in an effective atmospheric ducting zone with favorable reflector and critical level conditions, which were the primary causes of the long lives of the waves. Finally, numerical experiments to test the sensitivity to terrain and diabatic heating were conducted, and the results suggested a cooperative effect of terrain and diabatic heating contributed to the propagation and enhancement of the waves.

Influence of Interannual Variability of Antarctic Sea-Ice on Summer Rainfall in Eastern China

Based on the Antarctic sea-ice coverage reanalysis data from the Hadlcy Center and other observational data during the 30-year period from 1969 to 1998, it is shown that Antarctic sea-ice coverage exhibits considerable interannual variability with a complex relation to El Ni?o and the South Oscillation (ENSO). Besides this, the ice maintains the seasonal persistence of the atmospheric circulation in high latitudes of the Southern Hemisphere. Thus it can be used as a predictor in short-term climate prediction. Both correlation and time series analyses demonstrate that summer rainfall in eastern China is closely related to Antarctic sea-ice coverage. When it is extended during boreal spring through summer, there is more rainfall in the lower reaches of the Yellow River of North China, and in contrast, less rainfall is found in the Zhujiang River basin of South China and Northeast China. A further analysis indicates that this rainfall pattern is related to the intensity of the East Asian summer monsoon caused by interannual variability of Antarctic sea-ice coverage.

A Three-dimensional Wave Activity Flux of Inertia–Gravity Waves and Its Application to a Rainstorm Event

A three-dimensional transformed Eulerian-mean(3D TEM) equation under a non-hydrostatic and non-geostrophic assumption is deduced in this study. The vertical component of the 3D wave activity flux deduced here is the primary difference from previous studies, which is suitable to mesoscale systems. Using the 3D TEM equation, the energy propagation of the inertia–gravity waves and how the generation and dissipation of the inertia–gravity waves drive the mean flow can be examined. During the mature stage of a heavy precipitation event, the maximum of the Eliassen–Palm(EP) flux divergence is primarily concentrated at the height of 10–14 km, where the energy of the inertia–gravity waves propagates forward(eastward) and upward. Examining the contribution of each term of the 3D TEM equation shows that the EP flux divergence is the primary contributor to the mean flow tendency. The EP flux divergence decelerates the zonal wind above and below the high-level jet at the height of 10 km and 15 km, and accelerates the high-level jet at the height of 12–14 km. This structure enhances the vertical wind shear of the environment and promotes the development of the rainstorm.

CHARACTERISTICS OF THE LATENT HEAT DUE TO DIFFERENT CLOUD MICROPHYSICAL PROCESSES AND THEIR INFLUENCE ON AN AUTUMN HEAVY RAIN EVENT OVER HAINAN ISLAND

We analyzed cloud microphysical processes' latent heat characteristics and their influence on an autumn heavy rain event over Hainan Island,China,using the mesoscale numerical model WRF and WRF-3DVAR system.We found that positive latent heat occurred far above the zero layer,while negative latent heat occurred mainly under the zero layer.There was substantially more positive latent heat than negative latent heat,and the condensation heating had the most important contribution to the latent heat increase.The processes of deposition,congelation,melting and evaporation were all characterized by weakening after their intensification;however,the variations in condensation and sublimation processes were relatively small.The main cloud microphysical processes for positive latent heat were condensation of water vapor into cloud water,the condensation of rain,and the deposition increase of cloud ice,snow and graupel.The main cloud microphysical processes for negative latent heat were the evaporation of rain,the melting and enhanced melting of graupel.The latent heat releases due to different cloud microphysical processes have a significant impact on the intensity of precipitation.Without the condensation and evaporation of rain,the total latent heating would decrease and the moisture variables and precipitation would reduce significantly.Without deposition and sublimation,the heating in high levels would decrease and the precipitation would reduce.Without congelation and melting,the latent heating would enhance in the low levels,and the precipitation would reduce.

Impact of the Preceding Boreal Winter Southern Annular Mode on the Summertime Somali Jet

One of the major high-latitude circulation systems in the Southern Hemisphere is the Southern Annular Mode(SAM). Its effect on the Somali Jet(SMJ), which connects the Southern and Northern hemispheres, cannot be ignored. The present reported results show that time series of both the Southern Annular Mode Index(SAMI) during the preceding winter and the summertime Somali Jet intensity Index(SMJI) display a significant increasing trend and have similar interdecadal variation. The latter was rather strong around 1960, then became weaker up to the mid-1980 s, before starting to strengthen again. The lead-lag correlations of monthly mean SAMI with the following summertime SMJI showed significant positive correlations in November, December, and January. There are thus connections across two seasons between the SAM and the SMJ. The influence of the winter SAM on the summer SMJ was explored via analyses of SST anomalies in the Southern Indian Ocean. During strong(weak) SAM/SMJ years, the SST east of Madagascar is colder(warmer) while the SST west of Australia is warmer(colder), corresponding to the positive(negative) Southern Indian Ocean Dipole-like(SIODL) event. Subsequently, the SIODL excites an anticyclone located over the Arabian Sea in summer through air-sea coupling from winter to summer, which causes an increase in the summer SMJ intensity. The anticyclone/high branch of the SAM over the Southern Hemisphere subtropics and the cyclone/low over the east coast of Madagascar play an important role in the formation of Southern Indian Ocean "bridge" from winter to summer.

EFFECTS OF INDIAN OCEAN SSTA WITH ENSO ON WINTER RAINFALL IN CHINA

Based on Hadley Center monthly global SST,1960-2009 NCEP/NCAR reanalysis data and observation rainfall data over 160 stations across China,the combined effect of Indian Ocean Dipole(IOD)and Pacific SSTA(ENSO)on winter rainfall in China and their different roles are investigated in the work.The study focuses on the differences among the winter precipitation pattern during the years with Indian Ocean Dipole(IOD)only,ENSO only,and IOD and ENSO concurrence.It is shown that although the occurrences of the sea surface temperature anomalies of IOD and ENSO are of a high degree of synergy,their impacts on the winter precipitation are not the same.In the year with positive phase of IOD,the winter rainfall will be more than normal in Southwest China(except western Yunnan),North China and Northeast China while it will be less in Yangtze River and Huaihe River Basins.The result is contrary during the year with negative phase of IOD.However,the impact of IOD positive phase on winter precipitation is more significant than that of the negative phase.When the IOD appears along with ENSO,the ENSO signal will enhance the influence of IOD on winter precipitation of Southwest China(except western Yunnan),Inner Mongolia and Northeast China.In addition,this paper makes a preliminary analysis of the circulation causes of the relationship between IOD and the winter rainfall in China.

Model Uncertainty Representation for a Convection-Allowing Ensemble Prediction System Based on CNOP-P

Formulating model uncertainties for a convection-allowing ensemble prediction system(CAEPS)is a much more challenging problem compared to well-utilized approaches in synoptic weather forecasting.A new approach is proposed and tested through assuming that the model uncertainty should reasonably describe the fast nonlinear error growth of the convection-allowing model,due to the fast developing character and strong nonlinearity of convective events.The Conditional Nonlinear Optimal Perturbation related to Parameters(CNOP-P)is applied in this study.Also,an ensemble approach is adopted to solve the CNOP-P problem.By using five locally developed strong convective events that occurred in pre-rainy season of South China,the most sensitive parameters were detected based on CNOP-P,which resulted in the maximum variations in precipitation.A formulation of model uncertainty is designed by adding stochastic perturbations into these sensitive parameters.Through comparison ensemble experiments by using all the 13 heavy rainfall cases that occurred in the flood season of South China in 2017,the advantages of the CNOP-P-based method are examined and verified by comparing with the well-utilized stochastically perturbed physics tendencies(SPPT)scheme.The results indicate that the CNOP-P-based method has potential in improving the under-dispersive problem of the current CAEPS.

A THEORY OF BLOCKING FORMATION IN THE ATMOSPHERE

In this paper, a new theory of blocking formation was proposed. The nonlinear Schrdinger equation satisfied by nonlear barotropic Rossby waves for the weak shear zonal flow was obtained by using the WKB method. It was pointed out that when the Rossby wavenumbers sarisfied the relation: k/3<m^2<4k^2 (where k and m are the zonal and meridional wavenumbers respectively), the periodic Rossby wave in the atmosphere might produce the modulational instability and form the envelope Rossby solitary wave. Furthermore, the stream function field of the envelope Rossby solitary wave was calculated, and the structure derived here was similar to the dipole blocking in the atmosphere. On the other hand, we also pointed out that the dipole blocking might be caused through the Rossby wave modulational instability, moreover, the dipole blocking could persist for 25 days and disappear through energy dispersion of Rossby waves.

The test freezing temperature of C_2―C_6 dicarboxylic acid: The important indicator for ice nucleation processes

The importance of organic compounds as significant constituents of atmospheric aerosols, and cloud condensation nuclei (CCN), as well as players influencing the tropospheric oxidation and atmospheric energy budget, have been increasingly recognized. Low molecular weight dicarboxylic acids (LMW-DCAs) are significant identified portions of atmospheric condensed matter including aerosols, fog and clouds. Besides the photochemical transformation of DCA, the implication of organic matter in ice nucleation processes has been considered. In this study, we investigated the freezing temperature of pure and mixed (C2―C6) DCA solutions in ultra-pure water and tap water solution droplets using a freezing nucleus counter at different pH, and in different water ionic conditions. The mean freezing temperature of different mixture of LMW-DCA in ultra-pure and tap water solution droplets ranged from ?24.1±2.8 to ?21.3±3.9℃ and ?10.2±2.2 to ?9.5±2.2℃, respectively. The mean freezing temperature of the control (ultra-pure and tap) water droplets (?22.6±3.5℃, 11.2±2.4℃) was also measured. The results, and their implications in atmospheric chemistry and physics of the atmosphere will be discussed.

Building Extraction from High Resolution SAR Imagery in Urban Areas

In this paper, the textural characteristics of the buildings were quantified by using two texture descriptors, namely, Square Root Pair Difference （SRPD） and Gi ＊. Then, a novel method, based on SRPD and Gi ＊, to extract building areas in ur- ban areas from very high resolution SAR images is presented. The results showed that this method has the ability to differentiate buildings from the complicated features in urban areas, which can be employed for land mapping and provides support for relief operations.