广州灰霾现象特征分析

依据灰霾的发布和判定依据,对中山大学大气环境自动监测站的能见度、风速、相对湿度和ρ(PM2.5)等观测数据进行分析,分析其随时间变化的规律和相关性,得出近年来广州灰霾变化规律和多类特征.结果表明:近年来广州整体灰霾现象有所改善,且主要呈现非夏季和夏季2种典型季节性特征.非夏季灰霾具有持续时间长、状态稳定和风力突破性强等特点;夏季灰霾具有持续期短、状态变化快,ρ(PM2.5)与能见度的曲线图镜像对称明显等规律;灰霾现象与城市空气质量有密切的关系,且API大于100的时间与较严重灰霾日的分布相似.

某医院楼宇自控系统中中央空调冷却水系统节能措施的实现

本文介绍在工程实践中,利用楼宇自动化系统技术对中央空调冷却水系统中的冷却塔进行节能控制的一种策略的算法。

Impact of Trans-Atlantic-Pacific Ocean Dipole–like pattern on summer precipitation variability over West Africa

Recent findings indicate that rainfall variability over West Africa is characterized by more positive anomalies in the last four decades.The authors demonstrate that the recent interannual rainfall variability is linked to an air–sea phenomenon that occurs in the tropical Atlantic and eastern Pacific Ocean,and then propose the Trans-Atlantic-Pacific Ocean Dipole(TAPOD)index as a measure for this tropical ocean phenomenon,which is found to be closely correlated with the West African summer rainfall anomalies.Using observational and reanalysis datasets,composite analysis suggests that enhanced precipitation in West Africa is associated with the positive phase of the TAPOD,which is characterized by warm sea surface temperature anomalies(SSTAs)in the tropical Atlantic and cool SSTAs in the tropical eastern Pacific Ocean.During the positive phase of the TAPOD,there are significant westerly anomalies over the tropical Atlantic Ocean,which drives anomalous water vapor convergence over West Africa,leading to enhanced precipitation in the region.

Atmospheric diabatic heating–induced wave train from the Caspian Sea to South and East Asia during the summer monsoon season

During the summer monsoon season,the authors observe a wave train that stretches from the northern Arabian Peninsula and Caspian Sea to the Indo-Gangetic plains along the foothills of the Himalaya and extending further east of the Tibetan Plateau.The trend analysis between 1979 and 2018 with NCEP–NCAR reanalysis data show that the diabatic heating flux(averaged over 1000 to 500 hPa)tends to decrease significantly over the Caspian Sea and its surrounding regions.In addition,the sea level pressure is increasing by^0.1 hPa yr-1 over the Caspian Sea,forming a high-pressure divergent center over there.The divergent center is collocated with an anticyclonic circulation trend at 850 hPa over the Caspian Sea.This decreasing diabatic heating flux modulates the local atmospheric circulation by increasing the surface pressure around the center of divergence,which further facilitates a wave train to propagate towards South and East Asia.This wave train transports the moisture fluxes at 925 h Pa from the Caspian Sea,southeastward towards the South and East Asian monsoon region.

The effects of asymmetric potential vorticity forcing on the instability of South Asia High and Indian summer monsoon onset

Based on the theory of potential vorticity(PV),the unstable development of the South Asia High(SAH)due to diabatic heating and its impacts on the Indian Summer Monsoon(ISM)onset are studied via a case diagnosis of 1998.The Indian Summer Monsoon onset in 1998 is related to the rapidly strengthening and northward moving of a tropical cyclone originally located in the south of Arabian Sea.It is demonstrated that the rapid enhancement of the cyclone is a consequence of a baroclinic development characterized by the phase-lock of high PV systems in the upper and lower troposphere.Both the intensification of the SAH and the development of the zonal asymmetric PV forcing are forced by the rapidly increasing latent heat released from the heavy rainfall in East Asia and South East Asia after the onsets of the Bay of Bengal(BOB)monsoon and the South China Sea(SCS)monsoon.High PV moves southwards along the intensified northerlies on the eastern side of the SAH and travels westwards on its south side,which can reach its northwest.Such a series of high PV eddies are transported to the west of the SAH continuously,which is the main source of PV anomalies in the upper troposphere over the Arabian Sea from late spring to early summer.A cyclonic curvature on the southwest of the SAH associated with increasing divergence,which forms a strong upper tropospheric pumping,is generated by the anomalous positive PV over the Arabian Sea on 355 K.The cyclone in the lower troposphere moves northwards from low latitudes of the Arabian Sea,and the upper-layer high PV extends downwards and southwards.Baroclinic development thus occurs and the tropical low-pressure system develops into an explosive vortex of the ISM,which leads to the onset of the ISM.In addition,evolution of subtropical anticyclone over the Arabian Peninsula is another important factor contributing to the onset of the ISM.Before the onset,the surface sensible heating on the Arabian Peninsula is very strong.Consequently the subtropical anticyclone which dominated the Arabian Sea in spring retreats westwards to the Arabian Peninsula and intensifies rapidly.The zonal asymmetric PV forcing develops gradually with high PV eddies moving southwards along northerlies on the eastern side of the anticyclone,and a high PV trough is formed in the middle troposphere over the Arabian Sea,which is favorable to the explosive barotropic development of the tropical cyclone into the vortex.Results from this study demonstrate that the ISM onset,which is different from the BOB and the SCS monsoon onset,is a special dynamical as well as thermodynamic process occurring under the condition of fully coupling of the upper,middle,and lower tropospheric circulations.