THERMAL FORCING IMPACTS OF THE EASTERLY VORTEX ON THE EAST-WEST SHIFT OF THE SUBTROPICAL ANTICYCLONE OVER WESTERN PACIFIC OCEAN

By employing the NCEP/NCAR reanalysis data sets(1 000 to 10 hPa,2.5°× 2.5°),the thermal forcing impacts are analyzed of an easterly vortex(shortened as EV) over the tropical upper troposphere on the quasi-horizontal movement of the Western Pacific Subtropical Anticyclone(shortened as WPS A) during 22-25 June 2003.The relevant mechanisms are discussed as well.It is shown that the distribution and intensity of the non-adiabatic effect near the EV result in the anomalous eastward retreat of the WPSA.The WPSA prefers extending to the colder region,i.e.,it moves toward the region in which the non-adiabatic heating is weakening or the cooling is strengthening.During the WPSA retreat,the apparent changes of non-adiabatic heating illustrate the characteristics of enhanced cooling in the east side of the EV.Meanwhile,the cooling in the west side exhibits a weakened eastward trend,most prominently at 300 hPa in the troposphere.The evidence on the factors causing the change in thermal condition is found:the most important contribution to the heating-rate trend is the vertical transport term,followed in turn by the local change in the heating rate term and the horizontal advection term.As a result,the atmospheric non-adiabatic heating generated by the vertical transport and local change discussed above is mainly connected to the retreat of the WPSA.

Predecessor Rain Events in the Yangtze River Delta Region Associated with South China Sea and Northwest Pacific Ocean(SCS-WNPO)Tropical Cyclones

Predecessor rain events(PREs) in the Yangtze River Delta(YRD) region associated with the South China Sea and Northwest Pacific Ocean(SCS-WNPO) tropical cyclones(TCs) are investigated during the period from 2010 to 2019.Results indicate that approximately 10% of TCs making landfall in China produce PREs over the YRD region;however,they are seldom forecasted. PREs often occur over the YRD region when TCs begin to be active in the SCS-WNPO with westward paths, whilst the cold air is still existing or beginning to be present. PREs are more likely to peak in June and September. The distances between the PRE centers and the parent TC range from 900 to 1700 km. The median value of rain amounts and the median lifetime of PREs is approximately 200 mm and 24 h, respectively. Composite results suggest that PREs form in the equatorward jet-entrance region of the upper-level westerly jet(WJ), where a 925-hPa equivalent potential temperature ridge is located east of a 500-hPa trough. Deep moisture is transported from the TC vicinity to the remote PREs region. The ascent of this deep moist air in front of the 500-hPa trough and frontogenesis beneath the equatorward entrance region of the WJ is advantageous for the occurrence of PREs in the YRD region. The upper-level WJ may be affected by the subtropical high and westerly trough in the Northwest Pacific Ocean, and the occurrence of PREs may favor the maintenance of the upper-level WJ. The upper-level outflow of TCs in the SCS plays a secondary role.

Efficiently Improving Ensemble Forecasts of Warm-Sector Heavy Rainfall over Coastal Southern China: Targeted Assimilation to Reduce the Critical Initial Field Errors

Warm-sector heavy rainfall events over southern China are difficult to accurately forecast, due in part to inaccurate initial fields in numerical weather prediction models. In order to determine an efficient way of reducing the critical initial field errors, this study conducts and compares two sets of 60-member ensemble forecast experiments of a warm-sector heavy rainfall event over coastal southern China without data assimilation(NODA) and with radar radial velocity data assimilation(RadarDA). Yangjiang radar data, which can provide offshore high-resolution wind field information, were assimilated by using a Weather Research and Forecasting(WRF)-based ensemble Kalman filter(EnKF) system. The results show that the speed and direction errors of the southeasterly airflow in the marine boundary layer over the northern South China Sea may primarily be responsible for the forecast errors in rainfall and convection evolution. Targeted assimilation of radial velocity data from the Yangjiang radar can reduce the critical initial field errors of most members, resulting in improvements to the ensemble forecast. Specifically, RadarDA simulations indicate that radial-velocity data assimilation(VrDA) can directly reduce the initial field errors in wind speed and direction, and indirectly and slightly adjust the initial moisture fields in most members, thereby improving the evolution features of moisture transport during the subsequent forecast period. Therefore, these RadarDA members can better capture the initiation and development of convection and have higher forecast skill for the convection evolution and rainfall. The improvement in the deterministic forecasts of most members results in an improved overall ensemble forecast performance. However, VrDA sometimes results in inappropriate adjustment of the initial wind field,so the forecast skill of a few members decreases rather than increases after VrDA. This suggests that a degree of uncertainty remains about the effect of the WRF-based EnKF system. Moreover, the results further indicate that accurate forecasts of the convection evolution and rainfall of warm-sector heavy rainfall events over southern China are challenging.

Structures of convection and turbulent kinetic energy in boundary layer over the southeastern edge of the Tibetan Plateau

Based on a comprehensive analysis on Sonic Anemometer and gradient data, wind profile radar(WPR) and GPS sounding data of March–August 2008 from the boundary layer(BL) tower observation system at Dali on the southeastern edge of Tibetan Plateau(TP), it is found that the strengths of turbulent kinetic energy(TKE), buoyancy term and shear term depend on vegetation cover in association with local stability and thermodynamic condition. Strong kinetic turbulence appears when near surface layer in neutral condition with the large contribution from shear term. In an unstable condition within near surface layer, the atmospheric turbulent motion is mainly thermal turbulence, as buoyancy term is obviously larger than shear term. Under a stable condition the intermittent turbulence is accompanied by weak shear and buoyancy term, and TKE is significantly less than neutral or instable condition. The study also presents that the buoyancy term contribution at Nyingchi station in the southern slopes of the TP large topography in spring is significantly larger than that at Dali over the southeastern TP edge, reflecting that the thermal turbulence makes an important contribution to convection activity in the southern slopes of TP. Dali station is located in complex terrain with mountain and valley leading to larger kinetic turbulence. From the perspective of interaction of turbulence-convection in different scales, the study revealed that the height of convective boundary layer(CBL) could reach up to 1500–2000 m. TKE, shear term, and buoyancy term in near surface layer have the notable correlations with BL height and local vertical motion. The daytime thermodynamic turbulence effect of heat flux and buoyancy term has an obvious impact on the height of CBL, whereas mechanical turbulence only exerts a less impact. Mechanical turbulence in near surface layer has a significant impact on vertical motion especially in the forenoon with impacting height of 2500–3000 m. The peaks in diurnal variations of shear term and buoyancy term correspond to the high instable periods, especially in summer forenoon. Our observation analysis characterized the convection activity triggered by TKE source and their interaction in the southeastern TP edge.

Case study of longwave contribution to dust radiative effects over East Asia

In order to evaluate the impacts of LW contribution to aerosol radiative effects over East Asia,a dust longwave radiative parameterization scheme is integrated into the online mesoscale dust forecasting model GRAPES_CUACE/dust.A case modeling study shows that about half at surface and one third at TOA of the dust negative shortwave radiative forcing are cancelled by its positive longwave forcing over the dust affected area.In the dust layer,longwave radiation emitting by dust cools the atmosphere,which counteracts about 17%of shortwave heating of atmosphere during daytime and results in cooling of atmosphere simply during nighttime.At the same time,the atmosphere beyond the dust layer is warmed because of absorbing the LW radiation emitted by dust layer.Dust longwave contribution exerts more evident impact on the air temperature in lower atmosphere and surface.The surface air temperature cooling rate resulting from the dust solar radiation is cancelled about 40%by dust longwave warming at daytime.At nighttime,dust longwave contribution warms land and sea surface.The online calculation of dust LW radiation reduces about 15%relative errors of predicted AOD based on the dust model with only SW radiative feedback.This case study result suggests that dust longwave contribution has important impacts on the earth-atmosphere energy process,especially on the surface and in the lower atmosphere and should not be neglected in the study of dust radiation effects.

Impact of Updraft on Neutralized Charge Rate by Lightning in Thunderstorms:A Simulation Case Study

The rate of neutralized charge by lightning（RNCL） is an important parameter indicating the intensity of lightning activity.The total charging rate（CR）,the CR of one kind of polarity（e.g.,negative） charge（CROP）,and the outflow rate of charge on precipitation（ORCP） are proposed as key factors impacting RNCL,based on the principle of conservation of one kind of polarity charge in a thunderstorm.In this paper,the impacts of updraft on CR and CROP are analyzed by using a 3D cloud resolution model for a strong storm that occurred in Beijing on 6 September 2008.The results show that updraft both promotes and inhibits RNCL at the same time.（1） Updraft always has a positive influence on CR.The correlation coefficient between the updraft volume and CR can reach 0.96.Strengthening of the updraft facilitates strengthening of RNCL through this positive influence.（2） Strengthening of the updraft also promotes reinforcement of CROP.The correlation coefficient between the updraft volume and CROP is high（about0.9）,but this promotion restrains the strengthening of RNCL because the strengthening of CROP will,most of the time,inhibit the increasing of RNCL.（3） Additionally,increasing of ORCP depresses the strengthening of RNCL.In terms of magnitude,the peak of ORCP is equal to the peak of CR.Because precipitation mainly appears after the lightning activity finishes,the depression effect of ORCP on RNCL can be ignored during the active lightning period.

In-situ measurement of atmospheric CFC-11 at the Shangdianzi Global Atmosphere Watch(GAW) Regional Station

An in-situ GC-ECD system was used to measure halocarbons at Shangdianzi(SDZ) GAW regional station.In this paper,we reported observational results of atmospheric CFC-11(CCl3F) mixing ratios from April 2007 to March 2008.The CFC-11 time series showed large variability.Approximately 62% observed values were filtered as non-background data.The median,10% and 90% percentiles of CFC-11 background mixing ratios were 245.4 ppt(10-12 mol/mol),244.6 ppt and 246.1 ppt,respectively;whereas those of non-background CFC-11 mixing ratios were 254.7,246.6 and 272.1 ppt,respectively.Significant differences in background and non-background CFC-11 mixing ratios were observed between summer and autumn,mainly because of the CFC-11 stored in foam being prone to atmospheric release in hot seasons.Comparison of the SDZ data with the five AGAGE stations suggested agreement with mid-high latitude Northern Hemisphere stations MHD,THD and RPB.The SDZ data were higher than that of Southern Hemisphere stations CGO and SMO.Higher CFC-11 mixing ratios measured in different seasons were always associated with winds from the W-WSW-SW sector,indicating that the airflow coming from this wind sector has a positive contribution to CFC-11concentrations.The CFC-11 mixing ratios were higher in autumn and summer than in spring and winter,in which its mixing ratios were very close to the atmospheric background level.This was happened especially when airflow originated from the NNE-NE-ENE-E sector,indicating the air masses coming from these wind directions was relatively clean.

Development of an integrating sphere calibration method for Cimel sunphotometers in China aerosol remote sensing network

Based on the integrating sphere traced from the National Institute of Standards and Technology （NIST, USA）, a sphere calibration method and protocol for the China aerosol remote sensing network （CARSNET） Cimel sun photometer was established. Four CE318 sun photometers were verified using the proposed cal- ibration method and operational protocol. The calibration results showed that the instrument coefficients differed by less than 3% for visible （-5% for infrared） wavelengths from the original ones stated by Cimel Electronique. In situ validation experiment data showed that radiances at ±6° measured by sun collimator （aureole） were consistent with those measured by sky collimator （sky）, under both almucantar （ALMUC） and principal plane （PPLAN） scenarios. Differences at all wavelengths were less than 1%, indicating that the method and protocol are suitable for CARSNET field sun photometer calibration, and would benefit improvement of data quality and accuracy of network observations.

CHANGES IN MONSOON AND TROPICAL CYCLONE EXTREME PRECIPITATION IN SOUTHEAST CHINA FROM 1960 TO 2012

Using daily precipitation data from 110 stations in Southeast China from 1960 to 2012,the extreme precipitation(EP)events associated with monsoon and tropical cyclones were examined using the Objective Synoptic Analysis Technique.In Southeast China,the extreme precipitation associated with tropical cyclones(TEP),which mainly occur in the summer(July–September),accounted for 27.9%of the total extreme precipitation amount,with 40–50%in the coastal regions.While the regional mean TEP amount showed an inconspicuous trend,total EP and monsoon EP(MEP)both showed an increasing trend,with the MEP trend being statistically significant.Although there was little change in the frequency of tropical cyclones affecting Southeast China,the TEP contribution to frequency increased with increasing EP threshold and the frequency of TEP with daily precipitation of more than 300 mm showed an increasing trend in the background of global climate change.The upward trend in the highest-threshold TEP events presents a challenge for mitigation of the damage associated with tropical cyclones.

A Diagnostic Case Study on the Comparison Between the Frontal and Non-Frontal Convective Systems

Two major mesoscale convective clusters of different characters occurred during the heavy rainfall event in Guangxi Region and Guangdong Province on 20 June 2005,and they are preliminarily identified as a frontal mesoscale convective system（MCS1;a frontal cloud cluster） and a non-frontal MCS（MCS2;a warm sector cloud cluster）.Comparative analyses on their convective intensity,maintenance mechanism, and moist potential vorticity（MPV） structure were further performed.The convective intensity analysis suggests that the ascending motion in both the frontal MCS1 and the warm sector MCS2 was strong,so it is hard to conclude whether the intensity of the frontal convective cluster was stronger than that of the nonfrontal convective cluster,and their difference in precipitation might result from differences in their moisture conditions.The comparative analysis of the maintenance mechanisms of matured MCS1 and MCS2 show that in MCS1 there were strong northerly inflows at middle and upper levels,and the convection was mainly maintained through convective-symmetric instability;while in MCS2,the water vapor was abundant,and the convection was maintained by moist convective instability.The structural analysis of MPV indicates that（1） the two clusters were both potentially symmetric unstable at middle and low levels;（2） there were interactions between the cold/dry air and the warm/wet air in the frontal MCS1,and the interactions between the upper- and low-level jets in the warm sector MCS2;（3） the high- and low-level jets and moisture condition nearby the convective clusters exerted different impacts on the two types of convective systems, respectively.

Atmospheric sulfur hexafluoride in-situ measurements at the Shangdianzi regional background station in China

We present in-situ measurements of atmospheric sulfur hexafluoride（SF6） conducted by an automated gas chromatograph–electron capture detector system and a gas chromatography/mass spectrometry system at a regional background site, Shangdianzi,in China, from June 2009 to May 2011, using the System for Observation of Greenhouse gases in Europe and Asia and Advanced Global Atmospheric Gases Experiment（AGAGE）techniques. The mean background and polluted mixing ratios for SF6 during the study period were 7.22 × 10-12（mol/mol, hereinafter） and 8.66 × 10-12, respectively. The averaged SF6 background mixing ratios at Shangdianzi were consistent with those obtained at other AGAGE stations located at similar latitudes（Trinidad Head and Mace Head）, but larger than AGAGE stations in the Southern Hemisphere（Cape Grim and Cape Matatula）. SF6 background mixing ratios increased rapidly during our study period, with a positive growth rate at 0.30 × 10-12year-1. The peak to peak amplitude of the seasonal cycle for SF6 background conditions was 0.07 × 10-12, while the seasonal fluctuation of polluted conditions was 2.16 × 10-12. During the study period, peak values of SF6 mixing ratios occurred in autumn when local surface horizontal winds originated from W/WSW/SW/SWS/S sectors, while lower levels of SF6 mixing ratios appeared as winds originated from N/NNE/NE/ENE/E sectors.