Influence of urbanization on the thermal environment of meteorological station:Satellite-observed evidence

In this paper, five national meteorological stations in Anhui province are taken as typical examples to explore the effects of local urbanization on their thermal environment by using Landsat data from 1990 to 2010. Satellite-based land use/land cover(LULC), land surface temperature(LST), normalized difference vegetation index(NDVI) are used to investigate the effects. The study shows that LULC around meteorological stations changed significantly due to urban expansion. Fast urbanization is the main factor that affects the spatial-temporal distribution of thermal environment around meteorological stations. Moreover, the normalized LST and NDVI exhibit strong inverse correlations around meteorological stations, so the variability of LST can be monitored through evaluating the variability of NDVI. In addition, station-relocation plays an important role in improving representativeness of thermal environment. Notably, the environment representativeness was improved, but when using the data from the station to study climate change, the relocation-induced inhomogeneous data should be considered and adjusted. Consequently,controlling the scale and layout of the urban buildings and constructions around meteorological stations is an effective method to ameliorate observational thermal environment and to improve regional representativeness of station observation. The present work provides observational evidences that high resolution Landsat images can be used to evaluate the thermal environment of meteorological stations.

The Possible Influence of Stratospheric Sudden Warming on East Asian Weather

By analyzing the linkage of the Northern Annular Mode （NAM） anomaly to the East Asian jet and the East Asian trough during Stratospheric Sudden Warming （SSW）, the influence of SSW on East Asian weather is studied. The results show that the East Asian jet is strengthened and the East Asian trough is deepened during SSW. With the downward propagation of SSW, the strengthened East Asian jet and the East Asian trough would move southward, expand westward and gradually influence the area of north and northeastern China. This implies that the winter monsoon tends to be enhanced over East Asia during SSW.

Precipitation Chemistry and Corresponding Transport Patterns of Influencing Air Masses at Huangshan Mountain in East China

One hundred and ten samples of rainwater were collected for chemical analysis at the summit of Huangshan Mountain, a high-altitude site in East China, from July 2010 to June 2011. The volume-weighted-mean （VWM） pH for the whole sampling period was 5.03. SO2- and Ca2＋ were the most abundant anion and cation, respectively. The ionic concentrations varied monthly with the highest concentrations in winter/spring and the lowest in summer. Evident inter-correlations were found among most ions, indicating the common sources for some species and fully mixing characteristics of the alpine precipitation chemistry. The VWM ratio of [SO]-]/[NO3] was 2.54, suggesting the acidity of rainwater comes from both nitric and sulfuric acids. Compared with contemporary observations at other alpine continental sites in China, the precipitation at Huangshan Mountain was the least polluted, with the lowest ionic concentrations. Trajectories to Huangshan Mountain on rainy days could be classified into six groups. The rainwater with influencing air masses originating in Mongolia was the most polluted with limited effect. The emissions of Jiangxi, Anhui, Zhejiang and Jiangsu provinces had a strong influence on the overall rain chemistry at Huangshan Mountain. The rainwater with influencing air masses from Inner Mongolia was heavily polluted by anthropogenic pollutants.

Tropospheric NO_2 Columns over Northeastern North America: Comparison of CMAQ Model Simulations with GOME Satellite Measurements

We present comparisons of the NO2 regional Chemical Transport Model （CTM） simulations over North-eastern North America during the time period from May to September, 1998 with hourly surface NO2 observations and the NO2 columns retrieved from the GOME （Global Ozone Monitoring Experiment） satellite instrument. The model calculations were performed using the Mesoscale Meteorological Model 5 （MM5）, Sparse Matrix Operator Kernal Emissions （SMOKE）, and Community Multiscale Air Quality （CMAQ） modeling systems, using the emission data from the National Emissions Inventory （NEI） databases of 1996 （U.S.） and 1995 （Canada）. The major objectives were to assess the performance of the CMAQ model and the accuracy of the emissions inventories as they affected the simulations of this important short-lived atmospheric species. The modeled （NcMAQ） and measured （NGOME） NO2 column amounts, as well as their temporal variations, agreed reasonably well. The absolute differences （NcMAQ-NGOME） across the domain were between ±3.0×10^15 molecules cm^-2, but they were less than ±1.0×10^15 molecules cm^-2 over the majority （80%） of the domain studied. The overall correlation coefficient between the measurements and the simulations was 0.75. The differences were mainly ascribed to a combination of inaccurate emission data for the CTM and the uncertainties in the GOME retrievals. Of these, the former were the more easily identifiable.

Transient Characteristics of Residual Meridional Circulation during Stratospheric Sudden Warming

The residual meridional circulation derived from the transformed Eulerian-mean thermodynamic equation and continuity equation can be separated into two parts,the slowly varying diabatic circulation and the transient circulation,as demonstrated by others.We calculated and composite-analyzed the transient and diabatic circulation for 14 stratospheric sudden warming(SSW) events from 1979-2002 by using the daily ECMWF reanalysis data.Specifically,the transient residual meridional circulation was calculated both with and without inclusion of the eddy heat transport term in the transformed Eulerian-mean thermodynamic equation to investigate the importance of the eddy heat transport term.The results showed that calculations of transient residual meridional circulation present rapid variations during SSWs,with or without inclusion of the eddy heat transport term.Although the patterns of transient residual meridional circulation with the eddy heat transport term were similar to that without the eddy heat transport term during SSW,the magnitudes in the upper stratosphere and high-latitude regions differed.As for the diabatic circulation,its daily variations were small during SSW events,and its patterns were in agreement with its monthly average.

Simulation of the Effect of an Increase in Methane on Air Temperature

The infrared radiative effect of methane was analyzed using the 2D, interactive chemical dynamical radiative SOCRATES model of the National Center for Atmospheric Research. Then, a sensitivity experi ment, with the methane volume mixing ratio increased by 10%, was carried out to study the influence of an increase of methane on air temperature. The results showed that methane has a heating effect through the infrared radiative process in the troposphere and a cooling effect in the stratosphere. However, the cooling effect of the methane is much smaller than that of water vapor in the stratosphere and is negligible in the mesosphere. The simulation results also showed that when methane concentration is increased by 10%, the air temperature lowers in the stratosphere and mesosphere and increases in the troposphere. The cooling can reach 0.2 K at the stratopause and can vary from 0.2-0.4 K in the mesosphere, and the temperature rise varies by around 0.001-0.002 K in the troposphere. The cooling results from the increase of the infrared radiative cooling rate caused by increased water vapor and O3 concentration, which are stimulated by the increase in methane in most of the stratosphere. The infrared radiation cooling of methane itself is minor. The depletion of O3 stimulated by the methane increase results indirectly in a decrease in the rate of so- lar radiation heating, producing cooling in the stratopause and mesosphere. The tropospheric warming is mainly caused by the increase of methane, which produces infrared radiative heating. The increase in H2O and O3 caused by the methane increase also contributes to a rise in temperature in the troposphere.

Simulation of the Effect of Water-vapor Increase on Temperature in the Stratosphere

To analyze the mechanism by which water vapor increase leads to cooling in the stratosphere, the effects of water-vapor increases on temperature in the stratosphere were simulated using the two-dimensional, interactive chemical dynamical radiative model （SOCRATES） of NCAR. The results indicate that increases in stratospheric water vapor lead to stratospheric cooling, with the extent of cooling increasing with height, and that cooling in the middle stratosphere is stronger in Arctic regions. Analysis of the radiation process showed that infrared radiative cooling by water vapor is a pivotal factor in middle-lower stratospheric cooling. However, in the upper stratosphere （above 45 km）, infrared radiation is not a factor in cooling; there, cooling is caused by the decreased solar radiative heating rate resulting from ozone decrease due to increased stratospheric water vapor. Dynamical cooling is important in the middle-upper stratosphere, and dynamical feedback to temperature change is more distinct in the Northern Hemisphere middle-high latitudes than in other regions and signiffcantly affects temperature and ozone in winter over Arctic regions. Increasing stratospheric water vapor will strengthen ozone depletion through the chemical process. However, ozone will increase in the middle stratosphere. The change in ozone due to increasing water vapor has an important effect on the stratospheric temperature change.

Summer Monsoon Impacts on Chlorophyll-a Concentration in the Middle of the South China Sea:Climatological Mean and Annual Variability

Climatological mean and annual variations of Chlorophyll-a(Chl-a) distribution,sea surface wind(SSW),and sea surface temperature(SST) from 1998 to 2008 were analyzed in the middle of the South China Sea(SCS),focusing on the typical region off the east coast of Vietnam(8.5-14°N,109.5-114°E).Based on remote sensing data and SCS summer monsoon index(SCSSMI) data,high Chl-a concentrations in the middle of the SCS in the southwest summer monsoon season(June-September) may be related to strong Ekman pumping and strong wind stress.The maximum of the monthly averaged climatological Chl-a in the summer appeared in August.According to the annual variation,there was a significant negative correlation(r =-0.42) between the SCSSMI and SST,a strongly positive correlation(r=0.61) between the SCSSMI and Chl-a,and a strongly negative correlation(r =-0.74) between the SST and Chl-a in the typical region off the east coast of Vietnam during 1998-2008.Due to the El Ni?o event specifically,the phenomena of a low Chl-a concentration,high SST and weak SCSSMI were extremely predominant in the summer of 1998.These relationships imply that the SCSSMI associated with the SST could be used to predict the annual variability of summer Chl-a in the SCS.

Bias Correction of Channel Brightness Temperature of FY-4A Hyperspectral GIIRS Based on Machine Learning

Data assimilation algorithm depends on the basic assumption of unbiased observation error,so bias correction is one of the important steps in satellite data processing.In this paper,using the geostationary interferometric infrared sounder(GIIRS)of FengYun-4 A(FY-4 A)observation and simulated brightness temperature based on background field,the brightness temperature bias correction of GIIRS channel is carried out based on random forest(RF)and extreme gradient boosting(XGBoost)machine learning.Based on the case data of Typhoon"Haishen",the correction effect of machine learning method is compared with Harris and Kelly’s"off-line"method,and the importance of different predictors to the bias correction is further discussed.The experimental results show that the systematic bias is effectively corrected,and the following conclusions are obtained:the correction effect is improved by adding geographic information(longitude and latitude)into the predictors;under the given combination of predictors,the correction effect of XGBoost is the best,followed by random forest,and finally offline method,but the three methods can correct the bias effectively;compared with long wave data of FY-4 A/GIIRS,machine learning may be more feasible for medium wave data bias correction.

Squall Line and Its Vertical Motion Under Different Moisture Profiles in Eastern China

The impacts of different moisture profiles on the structure and vertical motion of squall lines were investigated by conducting a set of numerical simulations.The base state was determined by an observational sounding,with high precipitable water representing moist environmental conditions in the East Asian monsoon region.To reveal the impact of moisture at different levels,the moisture content at the middle and low levels were changed in the numerical simulations.The numerical results showed that more convective cells developed and covered a larger area in the high moisture experiments,which was characteristic of the convection during the Meiyu season in China.In addition,high moisture content at low levels favored the development of updrafts and triggered convection of greater intensity.This was demonstrated by the thermodynamic parameters,including Convective Available Potential Energy(CAPE),Lifted Index(LI),Lift Condensation Level(LCL),and Level of Free Convection(LFC).Dry air at middle levels led to strong downdrafts in the environment and updrafts in clouds.This could be because dry air at middle levels favors the release of latent heat,thereby promoting updrafts in clouds and downdrafts in the environment.Therefore,high relative humidity(RH)at low levels and low RH at middle levels favors updrafts in the cloud cores.Additionally,moist air at low levels and dry air at middle levels promotes the development of convective cells and the intensification of cold pool.The squall line can be organized by the outflow boundary induced by cold pool.The balance of cold pool and environmental wind shear is favorable for the maintenance and strengthening of squall lines.

Grid-cell Aerosol Direct Shortwave Radiative Forcing Calculated Using the SBDART Model with MODIS and AERONET Observations：An Application in Winter and Summer in Eastern China

Taking winter and summer in eastern China as an example application, a grid-cell method of aerosol direct radiative forcing（ADRF） calculation is examined using the Santa Barbara DISORT Atmospheric Radiative Transfer（SBDART） model with inputs from MODIS and AERONET observations and reanalysis data. Results show that there are significant seasonal and regional differences in climatological mean aerosol optical parameters and ADRF. Higher aerosol optical depth（AOD）occurs in summer and two prominent high aerosol loading centers are observed. Higher single scattering albedo（SSA） in summer is likely associated with the weak absorbing secondary aerosols. SSA is higher in North China during summer but higher in South China during winter. Aerosols induce negative forcing at the top of the atmosphere（TOA） and surface during both winter and summer, which may be responsible for the decrease in temperature and the increase in relative humidity.Values of ADRF at the surface are four times stronger than those at the TOA. Both AOD and ADRF present strong interannual variations; however, their amplitudes are larger in summer. Moreover, patterns and trends of ADRF do not always correspond well to those of AOD. Differences in the spatial distributions of ADRF between strong and weak monsoon years are captured effectively. Generally, the present results justify that to calculate grid-cell ADRF at a large scale using the SBDART model with observational aerosol optical properties and reanalysis data is an effective approach.

Mesocyclone Evolution and Differences between Isolated and Embedded Supercells

A total of 61 supercells with mesocyclones lasting for at least 6 volume scans were investigated. These storm parameters and mesocyclone parameters were counted and compared to determine the salient differences between isolated supercells and embedded supercells in different regions. The results showed that the mesocyclone parameters had different evolution characteristics in three stages of mesocyclone. The storm parameters, mesocyclone parameters and severe weather phenomenon had significantly differences between isolated supercells and embedded supercells. The mesocyclone parameter differences determined the differences in the reflectivity structure and weather phenomenon. The higher base and top of mesocyclone for isolated supercells indicated that the isolated supercells had higher maximum reflectivity, maximum reflectivity height, cell-based vertically integrated liquid and top of storm cell, and significantly higher probability of hail or large hail than the embedded supercells. The descending lower base of mesocyclone at its mature stage in the region of Jianghuai Plain indicated that the supercells in this region had a higher probability of mesocyclone-induced tornado.

VARIABILITY OF AEROSOL OPTICAL PROPERTIES OVER HEFEI DURING SEPTEMBER 1993 TO SEPTEMBER 1994

An 8-wavelength sun-photometer has been operated at Hefei (31.31°N, 117.17°E) to monitor optical properties of atmospheric aerosols. Altogether 133 solar spectral extinction data were ob- tained on clear days during the period from September 1993 through September 1994, In this pa- per, the feature of the sun-photometer is briefly described. A relative aureole method is intro- duced. which can be used to monitor temporal evolution of aerosol loading during the sun-pho- tometer calibration period. Temporal variabilities of spectral aerosol optical depths and Angstrom turbidity parameters are presented. Relation of these variabilities with synoptic and local meteoro- logical conditions are analyzed and discussed, From measured spectral aerosol optical depths under some representative atmospheric conditions, columnar aerosol size distributions have been retrieved by a linearly constrained inversion method. These typical columnar aerosol size distributions are al- so presented and discussed.

Climatological Characteristics of Summer Precipitation over East Asia Measured by TRMM PR:A Review

Precipitation is an important indicator of climate change and a critical process in the hydrological cycle, on both the global and regional scales. Methods of precipitation observation and associated analyses are of strategic importance in global climate change research. As the first space-based radar, the Tropical Rainfall Measuring Mission （TRMM） Precipitation Radar （PR） has been in operation for almost 17 years and has acquired a huge amount of cloud and pre- cipitation data that provide a distinctive view to help expose the nature of cloud and precipitation in the tropics and subtropics. In this paper we review recent advances in summer East Asian precipitation climatology studies based on long-term TRMM PR measurements in the following three aspects： （1） the three-dimensional structure of precipita- tion, （2） the diurnal variation of precipitation, and （3） the recent precipitation trend. Additionally, some importantprospects regarding satellite remote sensing of precipitation and its application in the near future are discussed.

Structural Characteristics of Atmospheric Temperature and Humidity inside Clouds of Convective and Stratiform Precipitation in the Rainy Season over East Asia

In this study, a merged dataset constructed from Tropical Rainfall Measuring Mission precipitation radar rain products and Integrated Global Radiosonde Archive data is used to investigate the thermal structural characteristics of convective and stratiform precipitation in the rainy season （May-August） of 1998-2012 over East Asia. The res- ults show that the storm tops for convective precipitation are higher than those for stratiform precipitation, because of the more unstable atmospheric motions for convective precipitation. Moreover, the storm tops are higher at 1200 UTC than at 0000 UTC over land regions for both convective and stratiform precipitation, and vice versa for ocean region. Additionally, temperature anomaly patterns inside convective and stratiform precipitating clouds show a neg- ative anomaly of about 0-2 K, which results in cooling effects in the lower troposphere. This cooling is more obvi- ous at 1200 UTC for stratiform precipitation. The positive anomaly that appears in the middle troposphere is more than 2 K, with the strongest warming at 300 hPa. Relative humidity anomaly patterns show a positive anomaly in the middle troposphere （700-500 hPa） prior to the occurrence of the two types of precipitation, and the increase in mois- ture is evident for stratiform precipitation.

The most typical shape of oceanic mesoscale eddies from global satellite sea level observations

In this research, we normalized the character- istics of ocean eddies by using satellite observation of the Sea Level Anomaly （SLA） data to determine the most typical shape of ocean eddies. This normalization is based on modified analytic functions with nonlinear optimal fitting. The most typical eddy is the Taylor vortex （~50%）, which exhibits a Gaussian-shaped exp（-r2） SLA and a vorticity distribution of （1-rZ）exp（-r2） as a function of the normalized radii r. The larger the amplitude of the eddy, the more likely the eddy is to be Gaussian-shaped. Furthermore, approximately 40% of ocean eddies are combinations of two Gaussian eddies with different parameters, but the composition of these types of eddies is more like a quadratic eddy than a Gaussian one. Only a small portion of oceanic eddies are pure quadratic eddies （ 〈 10%） with the same vorticity distribution as a Rankine vortex. We concluded that the Taylor vortex is a good approximation of the typical shape of ocean eddies.

A climatological comparison of column-integrated water vapor for the third-generation reanalysis datasets

The atmospheric reanalysis datasets have been widely used to understand the variability of atmospheric water vapor on various temporal and spatial scales for climate change research. The difference among a variety of reanalysis datasets, however, causes the uncertainty of corresponding results. In this study, the climatology of atmospheric column-integrated water vapor for the period from 2000 to 2012 was compared among three latest third-generation atmospheric reanalyses including European Centre for Medium-range Weather Forecasts Interim Re-Analysis(ERA-Interim), Modern-Era Retrospective Analysis for Research and Applications(MERRA), and Climate Forecast System Reanalysis(CFSR), while possible explanation on the difference between them was given. The results show that there are significant differences among three datasets in the multi-year global distribution, variation of interannual cycle, long-term trend and so on, though high similarity for principal mode describing the variability of water vapor. Over oceans, the characteristics of long-term CWV variability are similar, whereas the main discrepancy among three datasets is located around the equatorial regions of the Intertropical Convergence Zone, the South Pacific Convergence Zone and warm cloud area, which is related with the difference between reanalysis models for the scheme of convective parameterization, the treatment of warm clouds, and the assimilation of satellite-based observations. Moreover, these CWV products are fairly consistent with observations(satellite-based retrievals) for oceans. On the other hand, there are systematic underestimations about 2.5 kg/m2 over lands for all three CWV datasets, compared with radiosonde observations. The difference between models to solve land-atmosphere interaction in complex environment, as well as the paucity in radiosonde observations, leads to significant water vapor gaps in the Amazon Basin of South America, central parts of Africa and some mountainous regions. These results would help better understand the climatology difference among various reanalysis datasets better, and more properly choose water vapor datasets for different research requirements.

Measurement of HONO flux using the aerodynamic gradient method over an agricultural field in the Huaihe River Basin,China

To investigate nitrous acid(HONO)levels and potential HONO sources above crop rotation fields.The HONO fluxes were measured by the aerodynamic gradient(AG)method from 14 December 2019 to 2 January 2020 over an agricultural field in the Huaihe River Basin.The ambient HONO levels were measured at two different heights(0.15 and 1.5 m),showing a typical diurnal cycle with low daytime levels and high nighttime levels.The upward HONO fluxes were mostly observed during the day,whereas deposition dominated at night.The diurnal variation of HONO flux followed solar radiation,with a noontime maximum of 0.2 nmol/(m^(2)·sec).The average upward HONO flux of 0.06±0.17 nmol/(m^(2)·sec)indicated that the agricultural field was a net source for atmospheric HONO.The higher HONO/NO_(2)ratio and NO_(2)-to-HONO conversion rate close to the surface suggested that nocturnal HONO was formed and released near the ground.The unknown HONO source was derived from the daytime HONO budget analysis,with an average strength of 0.31 ppbV/hr at noontime.The surface HONO flux,which was highly correlated with the photolysis frequency J(NO_(2))(R^(2)=0.925)and the product of J(NO_(2))×NO_(2)(R^(2)=0.840),accounted for∼23%of unknown daytime HONO source.The significant correlation between HONO fluxes and J(NO_(2))suggests a light-driven HONO formation mechanism responsible for the surface HONO flux during daytime.

Relationship between Extreme Precipitation and Temperature in Two Different Regions:The Tibetan Plateau and Middle–East China

The change of extreme precipitation with temperature has regional characteristics in the context of global warming.In this study, radiosonde data, co-located rain gauge(RG) observations, and Tropical Rainfall Measuring Mission(TRMM) precipitation radar(PR) products are used to explore the relationship between extreme precipitation intensity and near-surface temperature in Middle–East China(MEC) and the eastern Tibetan Plateau(TP) during1998–2012. The results show that extreme precipitation intensity increases with increasing temperature at an approximate Clausius–Clapeyron(C–C) rate(i.e., water vapor increases by 7% as temperature increases by 1°C based on the C–C equation) in MEC and TP, but the rate of increase is larger in TP than in MEC. This is probably because TP(MEC) is featured with deep convective(stratiform) precipitation, which releases more(less) latent heat and strengthens the convection intensity on a shorter(longer) timescale. It is also found that when temperature is higher than 25°C(15°C) in MEC(TP), the extreme precipitation intensity decreases with rise of temperature, suggesting that the precipitation intensity does not always increase with warming. In this case, the limited atmospheric humidity and precipitable water could be the primary factors for the decrease in extreme precipitation intensity at higher temperatures.