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2012 Vol. 29, No. 3

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CCSC (climate change study in China)
The Local Atmosphere and the Turbulent Heat Transfer in the Eastern Himalayas
ZOU Han, LI Peng, MA Shupo, ZHOU Libo, ZHU Jinhuan
2012, 29(3): 435-440. doi: 10.1007/s00376-011-0233-2
To understand the local atmosphere and heat transfer and to facilitate the boundary-layer parameterization of numerical simulation and prediction, an observational campaign was conducted in the Eastern Himalayas in June 2010. The local atmospheric properties and near-surface turbulent heat transfers were analyzed. The local atmosphere in this region is warmer, more humid and less windy, with weaker solar radiation and surface radiate heating than in the Middle Himalayas. The near-surface turbulent heat transfer in the Eastern Himalayas is weaker than that in the Middle Himalayas. The total heat transfer is mainly contributed by the latent heat transfer with a Bowen ratio of 0.36, which is essentially different from that in the Middle Himalayas and the other Tibetan regions.
Sunglint Impact on Atmospheric Soundings from Hyperspectral Resolution Infrared Radiances
YAO Zhigang, Jun LI, Jinlong LI
2012, 29(3): 455-463. doi: 10.1007/s00376-011-1013-8
The mid-wave infrared band (3--5 m) has been widely used for atmospheric soundings. The sunglint impact on the atmospheric parameter retrieval using this band has been neglected because the reflected radiances in this band are significantly less than those in the visible band. In this study, an investigation of sunglint impact on the atmospheric soundings was conducted with Atmospheric InfraRed Sounder observation data from 1 July to 7 July 2007 over the Atlantic Ocean. The impact of sunglint can lead to a brightness temperature increase of 1.0 K for the surface sensitive sounding channels near 4.58 m. This contamination can indirectly cause a positive bias of 4 g kg-1 in the water vapor retrieval near the ocean surface, and it can be corrected by simply excluding those contaminated channels.
The East Pacific Wavetrain: Its Variability and Impact on the Atmospheric Circulation in the Boreal Winter
ZHOU Putian, SUO Lingling, YUAN Jiacan, TAN Benkui
2012, 29(3): 471-483. doi: 10.1007/s00376-011-0216-3
The East Pacific wavetrain (EPW) refers to here the intense stationary wave activity detected in the troposphere over the East Pacific and North America in 45 northern winters from 1958 to 2002. The EPW is generated in the lower troposphere over the East Pacific, propagating predominantly eastward into North America and slightly upward then eventually into the stratosphere. The intensity of the EPW varies from year to year and exhibits apparent decadal variability. For the period 1958--1964, the EPW was in its second maximum, and it was weakest for the period 1965--1975, then it was strongest for the period 1976--1987. After 1987, the EPW weakened again. The intensity and position of the members (i.e., the Aleutian low, the North American trough, and the North American ridge) of the EPW oscillate from time to time. For an active EPW versus a weak EPW, the Aleutian low deepens abnormally and shifts its center from the west to the east of the date line, in the middle and upper troposphere the East Asian trough extends eastward, and the Canadian ridge intensifies at the same time. The opposite is true for a weak EPW. Even in the lower stratosphere, significant changes in the stationary wave pattern are also observed. Interestingly the spatial variability of the EPW assumes a Pacific--North American (PNA)-like teleconnection pattern. It is likely that the PNA low-frequency oscillation is a reflection of the oscillations of intensity and position of the members of the EPW in horizontal direction.
Moisture Transport over the Arabian Sea Associated with Summer Rainfall over Pakistan in 1994 and 2002
Kalim ULLAH, GAO Shouting
2012, 29(3): 501-508. doi: 10.1007/s00376-011-0200-y
In this study, we aimed to elucidate the critical role of moisture transport affecting monsoon activity in two contrasting summers over the Arabian Sea during the years 1994, a relatively wet year, and 2002, a relatively dry year. A comprehensive diagnostic evaluation and comparisons of the moisture fields were conducted; we focused on the precipitation and evaporation as well as the moisture transport and its divergence or convergence in the atmosphere. Monthly mean reanalysis data were obtained from the National Centers for Environmental Prediction (NCEP-I and -II). A detailed evaluation of the moisture budgets over Pakistan during these two years was made by calculating the latent energy flux at the surface (E-P) from the divergence of the total moisture transport. Our results confirm the moisture supply over the Arabian Sea to be the major source of rainfall in Pakistan and neighboring regions. In 1994, Pakistan received more rainfall compared to 2002 during the summer monsoon. Moisture flow deepens and strengthens over Arabian Sea during the peak summer monsoon months of July and August. Our analysis shows that vertically integrated moisture transport flux have a significant role in supplying moisture to the convective centers over Pakistan and neighboring regions from the divergent regions of the Arabian Sea and the Bay of Bengal. Moreover, in 1994, a deeper vertically integrated moisture convergence progression occurred over Pakistan compared to that in 2002. Perhaps that deeper convergence resulted in a more intense moisture depression over Pakistan and also caused more rainfall in 1994 during the summer monsoon. Finally, from the water budget analysis, it has been surmised that the water budget was larger in 1994 than in 2002 during the summer monsoon.
A Numerical Study of the Interaction between Two Simultaneous Storms: Goni and Morakot in September 2009
WU Xian, FEI Jianfang, HUANG Xiaogang, ZHANG Xiang, CHENG Xiaoping, REN Jianqi
2012, 29(3): 561-574. doi: 10.1007/s00376-011-1014-7
Significant anomalous tracks were observed when the severe tropical storm Goni (0907) and typhoon Morakot (0908) in September 2009 were evaluated in short distances. The relationship between the two is regarded as a case of binary interaction. Based on an MM5 model (fifth-generation mesoscale model of Pennsylvania State University-National Center for Atmospheric Research), in this study a series of sensitivity experiments were designed to determine the binary interaction between them. The sensitivity of the storm characteristics to the binary interaction was demonstrated through modeling experiments with different TC intensities and sizes based on the bogus vortices initialization. Furthermore, the contributions of large-scale environmental flow and the effects of interaction between the motions of the cyclones were distinguished by numerical experiments using only one of the TC vortices. Results from these experiments show that Morakot (0908) had a greater impact on the motion of Goni (0907), whereas Goni (0907) had a relatively limited impact on Morakot (0908). At the upper level, the northeasterly jet flow in the third quadrant of Morakot (0908) enhanced the upper-level divergence of Goni (0907) and had an important role in maintaining and increasing Goni's (0907) intensity. And at the lower level, Morakot (0908), with strong convergence and ascending airflow, made a stable transport channel of southwesterly warm and wet flow, thus supporting the lower-level water vapor convergence of Goni (0907). Goni (0907), which was located upriver of the southwesterly flow, intercepted part of the water vapor transportation in the southwesterly flow, causing the water vapor convergence to strengthen while the water vapor convergence of Morakot (0908) weakened.
Retrieving Microphysical Properties and Air Motion of Cirrus Clouds Based on the Doppler Moments Method Using Cloud Radar
ZHONG Lingzhi, LIU Liping, DENG Min, ZHOU Xiuji
2012, 29(3): 611-622. doi: 10.1007/s00376-011-0112-x
Radar parameters including radar reflectivity, Doppler velocity, and Doppler spectrum width were obtained from Doppler spectrum moments. The Doppler spectrum moment is the convolution of both the particle spectrum and the mean air vertical motion. Unlike strong precipitation, the motion of particles in cirrus clouds is quite close to the air motion around them. In this study, a method of Doppler moments was developed and used to retrieve cirrus cloud microphysical properties such as the mean air vertical velocity, mass-weighted diameter, effective particle size, and ice content. Ice content values were retrieved using both the Doppler spectrum method and classic Z--IWC (radar reflectivity--ice water content) relationships; however, the former is a more reasonable method.
Predictability of the East Asian Winter Monsoon Interannual Variability as Indicated by the DEMETER CGCMS
LI Fei, WANG Huijun
2012, 29(3): 441-454. doi: 10.1007/s00376-011-1115-3
The interannual variability of East Asian winter monsoon (EAWM) circulation from the Development of a European Multi-Model Ensemble (MME) System for Seasonal to Inter-Annual Prediction (DEMETER) hindcasts was evaluated against observation reanalysis data. We evaluated the DEMETER coupled general circulation models (CGCMs)' retrospective prediction of the typical EAWM and its associated atmospheric circulation. Results show that the EAWM can be reasonably predicted with statistically significant accuracy, yet the major bias of the hindcast models is the underestimation of the related anomalies. The temporal correlation coefficient (TCC) of the MME-produced EAWM index, defined as the first EOF mode of 850-hPa air temperature within the EAWM domain (20--60N, 90--150E), was 0.595. This coefficient was higher than those of the corresponding individual models (range: 0.39--0.51) for the period 1969--2001; this result indicates the advantage of the super-ensemble approach. This study also showed that the ensemble models can reasonably reproduce the major modes and their interannual variabilities for sea level pressure, geopotential height, surface air temperature, and wind fields in Eurasia. Therefore, the prediction of EAWM interannual variability is feasible using multimodel ensemble systems and that they may also reveal the associated mechanisms of the EAWM interannual variability.
Interdecadal Change in the Antarctic Circumpolar Wave during 1951--2010
BIAN Lingen, LIN Xiang
2012, 29(3): 464-470. doi: 10.1007/s00376-011-1143-z
In this study, we defined an index of the Antarctic Circumploar Wave (ACW) and analyzed its variability for the period 1951--2010. A regime shift of the circumpolar westerly in the Southern Ocean and an interdecadal change of the ACW, which occurred around the mid-1970s, were identified. Associated with these changes, the variations of the ACW show three distinct sub-periods: 1951--1973, 1974--1980, and 1981--2010. They are characterized by different speeds, amplitudes, and wave structures. We briefly investigated possible mechanisms responsible for the different behaviors of the ACW during the three periods.
The Effect of Transient Eddy on Interannual Meridional Displacement of Summer East Asian Subtropical Jet
XIANG Yang, YANG Xiuqun
2012, 29(3): 484-492. doi: 10.1007/s00376-011-1113-5
Using ERA-40 reanalysis daily data for the period 1958--2002, this study investigated the effect of transient eddy (TE) on the interannual meridional displacement of summer East Asian subtropical jet (EASJ) by conducting a detailed dynamical diagnosis. The summer EASJ axis features a significant interannual coherent meridional displacement. Associated with such a meridional displacement, the TE vorticity forcing anomalies are characterized by a meridional dipole pattern asymmetric about the climatological EASJ axis. The TE vorticity forcing anomalies yield barotropic zonal wind tendencies with a phase meridionally leading the zonal wind anomalies, suggesting that they act to reinforce further meridional displacement of the EASJ and favor a positive feedback in the TE and time-mean flow interaction. However, The TE thermal forcing anomalies induce baroclinic zonal wind tendencies that reduce the vertical shear of zonal wind and atmospheric baroclinicity and eventually suppress the TE activity, favoring a negative feedback in the TE and time-mean flow interaction. Although the two types of TE forcing tend to have opposite feedback roles, the TE vorticity forcing appears to be dominant in the TE effect on the time-mean flow.
Torrential Rainfall Responses to Ice Microphysical Processes during Pre-Summer Heavy Rainfall over Southern China
SHEN Xinyong, LIU Jia, Xiaofan LI
2012, 29(3): 493-500. doi: 10.1007/s00376-011-1122-4
In this study, the effects of key ice microphysical processes on the pre-summer heavy rainfall over southern China during 3--8 June 2008 were investigated. A series of two-dimensional sensitivity cloud-resolving model simulations were forced with zonally uniform vertical velocity, zonal wind, horizontal temperature, and water vapor advection data from the National Centers for Environmental Prediction (NCEP)/Global Data Assimilation System (GDAS). The effects of key ice microphysical processes on the responses of rainfall to large-scale forcing were analyzed by comparing two sensitivity experiments with a control experiment. In one sensitivity experiment, ice crystal radius, associated with depositional growth of snow from cloud ice, was reduced from 100 μm in the control experiment to 50 μm, and in the other sensitivity experiment the efficiency of the growth of graupel from the accretion of snow was reduced to 50% from 100% in the control experiment. The results show that the domain-mean rainfall responses to these ice microphysical processes are stronger during the decay phase than during the onset and mature phases. During the decay phase, the increased mean rain rate resulting from the decrease in ice crystal radius is associated with the enhanced mean local atmospheric drying, the increased mean local hydrometeor loss, and the suppressed mean water vapor divergence. The increased mean rain rate caused by the reduction in accretion efficiency is related to the reduced mean water vapor divergence and the enhanced mean local hydrometeor loss.
Variations of the Summer Somali and Australia Cross-Equatorial Flows and the Implications for the Asian Summer Monsoon
ZHU Yali
2012, 29(3): 509-518. doi: 10.1007/s00376-011-1120-6
The temporal variations during 1948--2010 and vertical structures of the summer Somali and Australia cross-equatorial flows (CEFs) and the implications for the Asian summer monsoon were explored in this study. The strongest southerly and northerly CEFs exist at 925 hPa and 150 hPa level, respectively. The low-level Somali (LLS) CEFs were significantly connected with the rainfall in most regions of India (especially the monsoon regions), except in a small area in southwest India. In comparison to the climatology, the low-level Australia (LLA) CEFs exhibited stronger variations at interannual time scale and are more closely connected to the East Asian summer monsoon circulation than to the LLS CEFs. The East Asian summer monsoon circulation anomalies related to stronger LLA CEFs were associated with less water vapor content and less rainfall in the region between the middle Yellow River and Yangtze River and with more water vapor and more rainfall in southern China. The sea-surface temperature anomalies east of Australia related to summer LLA CEFs emerge in spring and persist into summer, with implications for the seasonal prediction of summer rainfall in East Asia. The connection between the LLA CEFs and East Asian summer monsoon rainfall may be partly due to its linkage with El Nino-Southern Oscillation. In addition, both the LLA and LLS CEFs exhibited interdecadal shifts in the late 1970s and the late 1990s, consistent with the phase shifts of Pacific Decadal Oscillation (PDO).
Simulations of the Motion of Tropical Cyclone-like Vortices in the Presence of Synoptic and Mesoscale Circulations
LUO Zhexian, PING Fan
2012, 29(3): 519-528. doi: 10.1007/s00376-011-1199-9
Initial mesoscale vortex effects on the tropical cyclone (TC) motion in a system where three components coexist (i.e., an environmental vortex (EV), a TC, and mesoscale vortices) were examined using a barotropic vorticity equation model with initial fields where mesoscale vortices were generated stochastically. Results of these simulations indicate that the deflection of the TC track derived from the initial mesoscale vortices was clearly smaller than that from the beta effect in 60% of the cases. However, they may have a more significant impact on the TC track under the following circumstances. First, the interaction between an adjacent mesoscale vortex and the TC causes the emergence of a complicated structure with two centers in the TC inner region. This configuration may last for 8 h, and the two centers undergo a cyclonic rotation to make the change in direction of the TC motion. Second, two mesoscale vortices located in the EV circulation may merge, and the merged vortex shifts into the EV inner region, intensifying both the EV and steering flow for the TC, increasing speed of the TC.
The Tropical Intraseasonal Oscillation in SAMIL Coupled and Uncoupled General Circulation Models
YANG Jing, BAO Qing, WANG Xiaocong, ZHOU Tianjun
2012, 29(3): 529-543. doi: 10.1007/s00376-011-1087-3
Simulations of tropical intraseasonal oscillation (TISO) in SAMIL, the Spectral Atmospheric Model from the Institute of Atmospheric Physics (IAP) State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG) coupled and uncoupled general circulation models were comprehensively evaluated in this study. Compared to the uncoupled model, the atmosphere--ocean coupled model improved the TISO simulation in the following aspects: (1) the spectral intensity for the 30--80-day peak eastward periods was more realistic; (2) the eastward propagation signals over western Pacific were stronger; and (3) the variance distribution and stronger signals of Kelvin waves and mixed Rossby gravity waves were more realistic. Better performance in the coupled run was assumed to be associated with a better mean state and a more realistic relationship between precipitation and SST. In both the coupled and uncoupled runs, the unrealistic simulation of the eastward propagation over the equatorial Indian Ocean might have been associated with the biases of the precipitation mean state over the Indian Ocean, and the unrealistic split of maximum TISO precipitation variance over the Pacific might have corresponded to the exaggeration of the double Intertropical Convergence Zone (ITCZ) structure in precipitation mean state. However, whether a better mean state leads to better TISO activity remains questionable. Notably, the northward propagation over the Indian Ocean during summer was not improved in the mean lead--lag correlation analysis, but case studies have shown some strong cases to yield remarkably realistic northward propagation in coupled runs.
Low-Frequency Coupled Atmosphere--Ocean Variability in the Southern Indian Ocean
FENG Junqiao, HU Dunxin, YU Lejiang
2012, 29(3): 544-560. doi: 10.1007/s00376-011-1096-2
The low-frequency atmosphere--ocean coupled variability of the southern Indian Ocean (SIO) was investigated using observation data over 1958--2010. These data were obtained from ECMWF for sea level pressure (SLP) and wind, from NCEP/NCAR for heat fluxes, and from the Hadley Center for SST. To obtain the coupled air-sea variability, we performed SVD analyses on SST and SLP. The primary coupled mode represents 43% of the total square covariance and is featured by weak westerly winds along 45--30S. This weakened subtropical anticyclone forces fluctuations in a well-known subtropical dipole structure in the SST via wind-induced processes. The SST changes in response to atmosphere forcing and is predictable with a lead-time of 1--2 months. Atmosphere--ocean coupling of this mode is strongest during the austral summer. Its principle component is characterized by mixed interannual and interdecadal fluctuations. There is a strong relationship between the first mode and Antarctic Oscillation (AAO). The AAO can influence the coupled processes in the SIO by modulating the subtropical high. The second mode, accounting for 30% of the total square covariance, represents a 25-year period interdecadal oscillation in the strength of the subtropical anticyclone that is accompanied by fluctuations of a monopole structure in the SST along the 35--25S band. It is caused by subsidence of the atmosphere. The present study also shows that physical processes of both local thermodynamic and ocean circulation in the SIO have a crucial role in the formation of the atmosphere--ocean covariability.
Improvement of Radar Quantitative Precipitation Estimation Based on Real-Time Adjustments to Z--R Relationships and Inverse Distance Weighting Correction Schemes
WANG Gaili, LIU Liping, DING Yuanyuan
2012, 29(3): 575-584. doi: 10.1007/s00376-011-1139-8
The errors in radar quantitative precipitation estimations consist not only of systematic biases caused by random noises but also spatially nonuniform biases in radar rainfall at individual rain-gauge stations. In this study, a real-time adjustment to the radar reflectivity--rainfall rates (Z--R) relationship scheme and the gauge-corrected, radar-based, estimation scheme with inverse distance weighting interpolation was developed. Based on the characteristics of the two schemes, the two-step correction technique of radar quantitative precipitation estimation is proposed. To minimize the errors between radar quantitative precipitation estimations and rain gauge observations, a real-time adjustment to the Z--R relationship scheme is used to remove systematic bias on the time-domain. The gauge-corrected, radar-based, estimation scheme is then used to eliminate non-uniform errors in space. Based on radar data and rain gauge observations near the Huaihe River, the two-step correction technique was evaluated using two heavy-precipitation events. The results show that the proposed scheme improved not only in the underestimation of rainfall but also reduced the root-mean-square error and the mean relative error of radar--rain gauge pairs.
Contribution of South China Sea Tropical Cyclones to an Increase in Southern China Summer Rainfall Around 1993
CHEN Jiepeng, WU Renguang, WEN Zhiping
2012, 29(3): 585-598. doi: 10.1007/s00376-011-1181-6
The increase in southern China summer rainfall around 1993 was accompanied by an increase in tropical cyclones that formed in the South China Sea. This study documents the connection of these two features. Our analysis shows that the contribution of tropical cyclones that formed in the South China Sea to southern China summer rainfall experienced a significant increase around 1993, in particular, along the coast and in the heavy rain category. The number of tropical cyclones that formed in the western North Pacific and entered the South China Sea decreased, and their contribution to summer rainfall was reduced in eastern part of southern China (but statistically insignificant). The increase in tropical cyclone-induced rainfall contributed up to ~30% of the total rainfall increase along the coastal regions. The increase of tropical cyclones in the South China Sea appears to be related to an increase in local sea surface temperature.
A Parameterized yet Accurate Model of Ozone and Water Vapor Transmittance in the Solar-to-near-infrared Spectrum
LIU Weiyi, QIU Jinhuan
2012, 29(3): 599-610. doi: 10.1007/s00376-011-1076-6
A parameterized transmittance model (PTR) for ozone and water vapor monochromatic transmittance calculation in the solar-to-near-infrared spectrum 0.3--4 μm with a spectral resolution of 5 cm-1 was developed based on the transmittance data calculated by Moderate-resolution Transmittance model (MODTRAN). Polynomial equations were derived to represent the transmittance as functions of path length and airmass for every wavelength~based on the least-squares method. Comparisons between the transmittances calculated using PTR and MODTRAN were made, using the results of MODTRAN as a reference. Relative root-mean-square error (RMSre) was 0.823% for ozone transmittance. RMSre values were 8.84% and 3.48% for water vapor transmittance ranges of 1--1×10-18 and 1--1×10-3, respectively. In addition, the Stratospheric Aerosol and Gas Experiment II (SAGEII) ozone profiles and University of Wyoming (UWYO) water vapor profiles were applied to validate the applicability of PTR model. RMSre was 0.437% for ozone transmittance. RMSre values were 8.89% and 2.43% for water vapor transmittance ranges of 1--1×10-18 and 1--1×10-6, respectively. Furthermore, the optical depth profiles calculated using the PTR model were compared to the results of MODTRAN. Absolute RMS errors (RMSab) for ozone optical depths were within 0.0055 and 0.0523 for water vapor at all of the tested altitudes. Finally, the comparison between the solar heating rate calculated from the transmittance of PTR and Line-by-Line radiative transfer model (LBLRTM) was performed, showing a maximum deviation of 0.238 K d-1 (6% of the corresponding solar heating rate calculated using LBLRTM). In the troposphere all of the deviations were within 0.08 K d-1. The computational speed of PTR model is nearly two orders of magnitude faster than that of MODTRAN.
The Sensitivity of Ground Surface Temperature Prediction to Soil Thermal Properties Using the Simple Biosphere Model (SiB2)}
ZHANG Xiaohui, GAO Zhiqiu, WEI Dongping
2012, 29(3): 623-634. doi: 10.1007/s00376-011-1162-9
Using the Simple Biosphere Model (SiB2), soil thermal properties (STP) were examined in a Tibetan prairie during the monsoon period to investigate ground surface temperature prediction. We improved the SiB2 model by incorporating a revised force-restore method (FRM) to take the vertical heterogeneity of soil thermal diffusivity (k) into account. The results indicate that (1) the revised FRM alleviates daytime overestimation and nighttime underestimation in modeled ground surface temperature (Tg), and (2) its role in little rainfall events is significant because the vertical gradient of k increases with increasing surface evaporation. Since the original formula of thermal conductivity (λ) in the SiB2 greatly underestimates soil thermal conductivity, we compared five algorithms of λ involving soil moisture to investigate the cause of overestimation during the day and underestimation at night on the basis of the revised FRM. The results show that (1) the five algorithms significantly improve Tg prediction, especially in daytime, and (2) taking one of these five algorithms as an example, the simulated Tg values in the daytime are closer to the field measurements than those in the nighttime. The differences between modeled Tg and field measurements are mostly within the margin of error of ±2 K during 3 August to 4 September 1998.
Impact of Precursor Levels and Global Warming on Peak Ozone Concentration in the Pearl River Delta Region of China
WEI Xiaolin, LIU Qian, Ka Se LAM, WANG Tijian
2012, 29(3): 635-645. doi: 10.1007/s00376-011-1167-4
The relationship between the emission of ozone precursors and the chemical production of tropospheric ozone (O3) in the Pearl River Delta Region (PRD) was studied using numerical simulation. The aim of this study was to examine the volatile organic compound (VOC)- or nitrogen oxide (NOx =NO+NO2)-limited conditions at present and when surface temperature is increasing due to global warming, thus to make recommendations for future ozone abatement policies for the PRD region. The model used for this application is the U.S. Environmental Protection Agency's (EPA's) third-generation air-quality modeling system; it consists of the mesoscale meteorological model MM5 and the chemical transport model named Community Multi-scale Air Quality (CMAQ). A series of sensitivity tests were conducted to assess the influence of VOC and NOx variations on ozone production. Tropical cyclone was shown to be one of the important synoptic weather patterns leading to ozone pollution. The simulations were based on a tropical-cyclone-related episode that occurred during 14--16 September 2004. The results show that, in the future, the control strategy for emissions should be tightened. To reduce the current level of ozone to meet the Hong Kong Environmental Protection Department (EPD) air-quality objective (hourly average of 120 ppb), emphasis should be put on restricting the increase of NOx emissions. Furthermore, for a wide range of possible changes in precursor emissions, temperature increase will increase the ozone peak in the PRD region; the areas affected by photochemical smog are growing wider, but the locations of the ozone plume are rather invariant.