Numerical simulations on atmospheric stability conditions and urban airflow at five climate zones in China

Due to the quick development of urbanization,it is important to provide a healthy urban environment for the dweller.Previous studies have obtained valuable conclusions of how to improve the urban airflow distribution under isothermal conditions.How to adopt and interpret those conclusions when considering the solar-induced atmospheric stability conditions have not been clarified yet.In this study,the characteristics of atmospheric stability condition and influence of diurnal varying solar-induced thermal effect on urban airflow inside the idealized building arrays were investigated at five cities located at five climate zones in China.Urban energy model,CitySim,was employed to simulate the annual distribution of solar-induced walls’temperatures inside the idealized building arrays.The diurnal varying wall temperatures at the hottest days were set as thermal boundary conditions in computational fluid dynamic(CFD)simulations.With albedo value of 0.5,the possibility of adopting the results from isothermal condition directly ranged from 7%to 11%for the five cities in China throughout the year.The unstable condition ocuppied from 19%to 24%annually and the stable condition of more than 40%annually was observed.Under the diurnal varying solar-induced thermal effect,the spatially-averaged air speeds and airflow patterns were significantly different from the isothermal conditions.The percent of Richardson number under different atmospheric stability conditions annually based on the Citysim simulation results indicated that the atmospheric stability was most likely determined by the local climate characteristics and albedo value rather than the building layouts at the five selected cities in China,but this should be further investigated when the shadow effects of surrounding buildings were considered in simulations.

Global static stability and its relation to gravity waves in the middle atmosphere

The global atmospheric static stability(N2)in the middle atmosphere and its relation to gravity waves(GWs)were investigated by using the temperature profiles measured by the Sounding of the Atmosphere using Broadband Emission Radiometry(SABER)instrument from 2002 to 2018.At low latitudes,a layer with enhanced N2 occurs at an altitude of^20 km and exhibits annual oscillations caused by tropopause inversion layers.Above an altitude of^70 km,enhanced N2 exhibits semiannual oscillations at low latitudes caused by the mesosphere inversion layers and annual oscillations at high latitudes resulting from the downward shift of the summer mesopause.The correlation coefficients between N2 and GW amplitudes can be larger than 0.8 at latitudes poleward of^40°N/S.This observation provides factual evidence that a large N2 supports large-amplitude GWs and indicates that N2 plays a dominant role in maintaining GWs at least at high latitudes of the middle atmosphere.This evidence also partially explains the previous results regarding the phase changes of annual oscillations of GWs at high latitudes.

Nolinear waves and their barotropic stability in the tropical ocean and atmosphere

In this paper, the nonlinear waves and their barotropic stability in the tropical ocean and atmosphere are studied with the qualitative theory of the ordinary differential equation. The relationship is derived between the stability of nonlinear waves with different frequencies and the basic currents and their horizontal shear in the tropical ocean and atmosphere.

Observation-based Estimation of Aerosol-induced Reduction of Planetary Boundary Layer Height

Radiative aerosols are known to influence the surface energy budget and hence the evolution of the planetary boundary layer. In this study, we develop a method to estimate the aerosol-induced reduction in the planetary boundary layer height （PBLH） based on two years of ground-based measurements at a site, the Station for Observing Regional Processes of the Earth System （SORPES）, at Nanjing University, China, and radiosonde data from the meteorological station of Nanjing. The observations show that increased aerosol loads lead to a mean decrease of 67.1 W m-2 for downward shortwave radiation （DSR） and a mean increase of 19.2 W m-2 for downward longwave radiation （DLR）, as well as a mean decrease of 9.6 W m-2 for the surface sensible heat flux （SHF） in the daytime. The relative variations of DSR, DLR and SHF are shown as a function of the increment of column mass concentration of particulate matter （PM2.5）. High aerosol loading can significantly increase the atmospheric stability in the planetary boundary layer during both daytime and nighttime. Based on the statistical relationship between SHF and PM2.5 column mass concentrations, the SHF under clean atmospheric conditions （same as the background days） is derived. In this case, the derived SHF, together with observed SHF, are then used to estimate changes in the PBLH related to aerosols. Our results suggest that the PBLH decreases more rapidly with increasing aerosol loading at high aerosol loading. When the daytime mean column mass concentration of PM2.5 reaches 200 mg m-2, the decrease in the PBLH at 1600 LST （local standard time） is about 450 m.

A Diagnostic Study of the Asymmetric Distribution of Rainfall during the Landfall of Typhoon Haitang(2005)

The precipitation during landfall of typhoon Haitang （2005） showed asymmetric structures （left side/right side of the track）. Analysis of Weather Research and Forecasting model simulation data showed that rainfall on the right side was more than 15 times stronger than on the left side. The causes were analyzed by focusing on comparing the water vapor flux, stability and upward motion between the two sides. The major results were as follows： （1） Relative humidity on both sides was over 80%, whereas the convergence of water vapor flux in the lower troposphere was about 10 times larger on the right side than on the left side. （2） Both sides featured conditional symmetric instability [MPV （moist potential vorticity） 〈0], but the right side was more unstable than the left side. （3） Strong （weak） upward motion occurred throughout the troposphere on the right （left） side. The Q vector diagnosis suggested that large-scale and mesoscale forcing accounted for the difference in vertical velocity. Orographic lift and surface friction forced the development of the asymmetric precipitation pattern. On the right side, strong upward motion from the forcing of different scale weather systems and topography caused a substantial release of unstable energy and the transportation of water vapor from the lower to the upper troposphere, which produced torrential rainfall. However, the above conditions on the left side were all much weaker, which led to weaker rainfall. This may have been the cause of the asymmetric distribution of rainfall during the landfall of typhoon Haitang.

辽西地区区域性大雾气候特征及分析预报(英文)

By using the fog data from 1995 to 2004 of four selected observation stations,the weather features of foggy days in Liaoxi area have been studied in this paper.The favorable surface and upper circulation for fog and its frequency have also been concluded from the statistic.In this paper,the forecasting index of fog,proposed on the basis of the condition and mechanism of the fog occurrence,has been tested by the 10-year analysis.Another test conducted by using the data of 1st July-31st December,2004 also gives a good result which has a vacancy rate of 22.2% and a miss rate of 5.1%.

Effect of air－sea temperature difference on the momentum exchange between air and sea for fetch－limited cases

The atmospheric boundaly layer over sea surface is simplified as mixed convection of turbulent boundary lay er flow over a horizontal plate, and the momentum exchange between wind and waves is also included in the model. Ef fects of wind speed, air-sea temperature difference and fetch on the momentum exchange between air and sea are re vealed. The turbulence model used in calculating boundary layer is an extended version of the Van Driest mixing lengthmodel, and a combined theoretical and semi-empirical approach is employed in estimating the effect of ocean waves. Forfetch-limited cases, i. e. wind blows off sea shore for a limited distance. fetch plays a fundamental role in the air-sea mo mentum exchange under different air-sea temperature conditions, which is not discussed in previous studies.

The bulk transfer coefficients in the permafrost region at the Tanggula Pass of Tibetan Plateau

This paper presents research on the surface drag coefficients, CD, and the bulk transfer coefficients of sensible heat flux, CH, in the permafrost region at the Tanggula Pass of the Tibetan Plateau. The data were obtained from the Open-Path Eddy Covariance System and the 10-m Automatic Weather Station （AWS） at the TGLMS site which supported by Cryosphere Research Station （Chinese Academy of Science） on the Qinghai-Xizang Plateau （Tibetan Plateau）. The characteristics of Co and CH in relation to atmospheric instability and wind velocity are discussed, and it was found that the bulk transfer coefficients varied with air conditions and were different in different months. However, the bulk transfer coefficients obtained from the eddy covariance system did not show a significant increasing trend with increasing atmospheric instability, and the bulk transfer coefficients did not change greatly with increasing wind velocity at 10 m.

Far-Infrared Laser Diagnostics in EAST

Structure, improvements and experiment results of a vertical three-channel far- in- frared （FIR） hydrogen cyanide （HCN） laser interferometer, operated routinely in EAST to measure the electron density profile, are presented. Moreover, a five-channel deuterium cyanide （DCN） laser interferometer was developed successfully. Some key issues confronted in development, including the economization of working gas and the solution to atmospheric absorption, are resolved and described in detail.

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.

Decadal Variability of Extreme Precipitation Days over Northwest China from 1963 to 2012

Daily precipitation data from 153 meteorological stations over Northwest China during summer from 1963 to 2012 were selected to analyze the spatiotemporal distribution of extreme summer precipitation frequency.The results show that the extreme precipitation frequency was regional dependent.Southern Gansu,northern Qinghai,and southern Shaanxi provinces exhibited a high extreme precipitation frequency and were prone to abrupt changes in the frequency.Northwest China was further divided into three sub-regions（northern,central,and southern） based on cluster analysis of the 50-yr extreme precipitation frequency series for each meteorological station.The extreme precipitation frequency changes were manifested in the northern region during the late 1970 s and in the central region from the end of the 1980 s to the 1990 s.The southern region fluctuated on a timescale of quasi-10 yr.This study also explored the mechanism of changes in extreme precipitation frequency.The results demonstrate that stratification stability,atmospheric water vapor content,and upward motion all affected the changes in extreme precipitation frequency.