Circulation Pattern Controls of Summer Temperature Anomalies in Southern Africa

This study investigates the relationship between circulation patterns and austral summer temperature anomalies in southern Africa. The results show that the formation of continental lows tends to increase the thickness of the lower atmosphere. Further, the distinct variabilities of high and low pressure under the circulation types, influence air mass advection from the adjacent oceans, as well as atmospheric stability over land. Stronger anticyclonic circulation at the western branch of the Mascarene high-pressure system enhances the low-level cold air advection by southeast winds,decreases the thickness, and lowers the temperature over a majority of the land in southern Africa. Conversely, a weaker Mascarene High, coupled with enhanced cyclonic activity in the southwest Indian Ocean increases low-level warm air advection and increases temperature anomalies over vast regions in southern Africa. The ridging of a closed South Atlantic anticyclone at the southern coast of southern Africa results in colder temperatures near the tip of southern Africa due to enhanced low-level cold air advection by southeast winds. However, when the ridge is weak and westerly winds dominate the southern coast of southern Africa, these areas experience temperature increases. The northward track of the Southern Hemisphere mid-latitude cyclone, which can be linked to the negative Southern Annular Mode, reduces the temperature in the southwestern part of southern Africa. Also, during the analysis period, El Ni?o was associated with temperature increases over the central parts of southern Africa;while the positive Indian Ocean dipole was linked to a temperature increase over the northeastern, northwestern, and southwestern parts of southern Africa.

Regional and Synoptic-scale Features Associated with Inactive Periods of the Summer Monsoon over South China

This paper presents an observational study of the physical processes responsible for the inactive period (break) of the summer monsoon over South China (SC). The break of the monsoon is defined by using the rainfall data over Hong Kong Meteorological parameters provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) for the period 1985-1990 are examined. Daily values of each parameter for the six years are then composited each day for the period of 5 days before to 1 day after the break. It is found that several days before the break, changes opposite to those occurred during the onset and active periods begin to take place. This suggests that a feedback mechanism is present which tends to restore the atmosphere to a more stable state. This mechanism may be initiated by the formation of convective clouds during the onset and active periods. These clouds then reduce the solar radiation to the ground, leading to a gradual drop in the temperature. This drop, together with the cooling of the atmosphere due to the large amounts of rainfall, causes the pressure over the SC region to become higher, which in turn induces a westward extension of the subtropical ridge. The decrease in temperature over SC may also shift the location of the heat source to the west, which leads to a concomitant westward shift of the convergence of the southerlies and results in less moisture-laden air reaching the SC region. The atmosphere then becomes unfavourable for heavy convection and therefore a break starts.

COMPARISONS OF THE WEST PACIFIC SUBTROPICAL HIGH AND THE SOUTH ASIA HIGH BETWEEN NCEP/NCAR AND ECMWF REANALYSIS DATASETS

Comparisons of the west Pacific subtropical high with the South Asia High are made using the NCEP/NCAR and ECMWF 500 hPa and 100 hPa monthly boreal geopotential height fields for the period 1961-2000. Discrepancies are found for the time prior to 1980. The west Pacific subtropical high in the NCEP/NCAR data is less intense than in ECMWF data before 1980. The range and strength of the west Pacific subtropical high variation described by the NCEP/NCAR data are larger than those depicted by ECMWF data. The same situation appears in the 100-hPa geopotential field. These discoveries suggest that the interdecadal variation of the two systems as shown by the NCEP/NCAR data may not be true. Besides, the South Asia High center in the NCEP/NCAR data is obviously stronger than in the ECMWF data during the periods 1969, 1979-1991 and 1992-1995. Furthermore, the range is larger from 1992 to 1995.

Eddies in the Northwest Subtropical Pacific and Their Possible Effects on the South China Sea

Based on an analysis of drifter data from the World Ocean Circulation Experiment during 1979-1998, the sizes of the eddies in the North subtropical Pacific are determined from the radii of curvature of the drifter paths calculated by using a non-linear curve fitting method. To support the drifter data results, Sea Surface Height from the TOPEX/POSEIDON and ERS2 satellite data are analyzed in connection with the drifter paths. It is found that the eddies in the North Pacific (18°-23°N and 125°-150°E) move westward at an average speed of approximately 0.098 ms-1 and their average radius is 176 km,with radii ranging from 98 km to 298 km. During the nineteen-year period, only 4 out of approximately 200 drifters (2%)actually entered the South China Sea from the area adjacent to the Luzon Strait (18°-22°N and 121°-125°E) in the winter. It is also found that eddies from the interior of the North Pacific are unlikely to enter the South China Sea through the Luzon Strait.

THE SOUTH CHINA SEA SUMMER MONSOON AND THE SEASONAL MODALITY AND WEST EXTENDING OF THE NORTHERN HEMISPHERE PACIFIC SUBTROPICAL HIGH

Based on the 4-layer dbl wavelet packet and shannon entropy decomposition /reconstruction method and the NCEP/NCAR daily reanalysis data set, the correlation between the South China Sea summer monsoon and the Northern Hemisphere Pacific subtropical high seasonal modality/shift xvas studied and discussed, and a corresponding summer monsoon frequency-band energy criterion was defined and introduced for diagnosing the Pacific subtropical high’s modality/shift. A few new phenomena and correlation between the South China Sea summer monsoon and the Northern Hemisphere Pacific subtropical high were also revealed and presented.

Community structure and species diversity dynamics of a subtropical evergreen broad-leaved forest in China:2005 to 2020

Here,we characterize the temporal and spatial dynamics of forest community structure and species diversity in a subtropical evergreen broad-leaved forest in China.We found that community structure in this forest changed over a 15-year period.Specifically,renewal and death of common species was large,with the renewal of individuals mainly concentrated within a few populations,especially those of Aidia canthioides and Cryptocarya concinna.The numbers of individual deaths for common species were concentrated in the small and mid-diameter level.The spatial distribution of community species diversity fluctuated in each monitoring period,showing a more dispersed diversity after the 15-year study period,and the coefficient of variation on quadrats increased.In 2010,the death and renewal of the community and the spatial variation of species diversity were different compared to other survey years.Extreme weather may have affected species regeneration and community stability in our subtropical monsoon evergreen broad-leaved forests.Our findings suggest that strengthening the monitoring and management of the forest community will help better understand the long-and short-term causes of dynamic fluctuations of community structure and species diversity,and reveal the factors that drive changes in community structure.

Reflection on the Construction of Tropical and South Subtropical Agricultural Experimental Station CATAS( Jiangmen)

This paper introduces the origin and progress of Tropical and South Subtropical Agricultural Comprehensive Experimental Station( hereinafter referred to as experimental station) CATAS( Jiangmen),formulates the thought for construction of experimental station,analyzes the restrictive factors and puts forward corresponding countermeasures in order to provide reference for the decision- making and implementation of constructing the experimental station.

Definition and characteristics of the south edge of the subtropical winter monsoon in East Asian

Based on observational daily data of 730 meteorological stations in China, the south edge of the subtropical winter monsoon is defined according to relevant criterion and its variation characteristics are analyzed. Results show that this south edge has obvious inter-annual variation characteristics and shows a northward moving tendency as a whole, but since the 21 st century it has moved southwards and date of the south edge entering winter becomes earlier. Wind fields of the anomalously northward south edge of the subtropical winter monsoon in East Asia has an obvious southerly wind component which prevents cold air from moving southward. The index of this south edge and winter temperature has a positive correlation. Climate warming might be the main reason for the northward movement of the south edge of the subtropical winter monsoon.

Analysis of the Role Played by Circulation in the Persistent Precipitation over South China in June 2010

South China （SC） experienced persistent heavy rain in June 2010. The climatic anomalies and related mechanism are analyzed in this study. Results show that the large-scale circulation pattern favorable for precipitation was maintained. In the upper level, the South Asian High and westerly jet stream provided a divergent circulation over SC. In the middle and low levels, an anomalous strong subtropical high （STH） extended to the South China Sea. The southwesterly monsoon flow along the northwest flank of the STH transported abundant water vapor from the western North Pacific, the Bay of Bengal, and the South China Sea to SC. The precipitation can be classified into two types： the West Siberia low （WSL）-induced low-level cyclone mode, and the STH-induced low-level jet mode. STH and WSL indices are defined to estimate the influence of these two systems, respectively. Analysis shows that both are critical for precipitation, but their respective contributions differ from year to year. In 2010, both were important factors for the heavy rainfall in June.

South Asian High and Asian-Pacific-American Climate Teleconnection

Growing evidence indicates that the Asian monsoon plays an important role in affecting the weather and climate outside of Asia. However, this active role of the monsoon has not been demonstrated as thoroughly as has the variability of the monsoon caused by various impacting factors such as sea surface temperature and land surface. This study investigates the relationship between the Asian monsoon and the climate anomalies in the Asian-Pacific-American （APA） sector. A hypothesis is tested that the variability of the upper-tropospheric South Asian high （SAH）, which is closely associated with the overall heating of the large-scale Asian monsoon, is linked to changes in the subtropical western Pacific high （SWPH）, the midPacific trough, and the Mexican high. The changes in these circulation systems cause variability in surface temperature and precipitation in the APA region. A stronger SAH is accompanied by a stronger and more extensive SWPH. The enlargement of the SWPH weakens the mid-Pacific trough. As a result, the southern portion of the Mexican high becomes stronger. These changes are associated with changes in atmospheric teleconnections, precipitation, and surface temperature throughout the APA region. When the SAH is stronger, precipitation increases in southern Asia, decreases over the Pacific Ocean, and increases over the Central America. Precipitation also increases over Australia and central Africa and decreases in the Mediterranean region. While the signals in surface temperature are weak over the tropical land portion, they are apparent in the mid latitudes and over the eastern Pacific Ocean.

Effects of the East Asian Summer Monsoon on Tropical Cyclone Genesis over the South China Sea on an Interdecadal Time Scale

Tropical cyclone （TC） genesis over the South China Sea （SCS） during 1965–2004 was analyzed. The locations of TC genesis display evident seasonal changes, with the mean position of formation situated north of 15 °N in summer （June–July–August） and south of 15 °N in autumn （September–October–November）. The TC genesis in summer underwent dramatic interdecadal variations, with more and less TC frequency during 1965–1974/1995–2004 and 1979–1993, respectively. In contrast, a significant interannual variation of TC genesis with a period of ～4 years was observed in autumn. This study investigated the relationship of SCS TC genesis to the East Asian jet stream （EAJS） and the western North Pacific subtropical high （WNPSH） on an interdecadal time scale. Analysis and comparison of the impacts of the EAJS and the WNPSH on vertical wind shear changes indicate that changes in the WNPSH and EAJS intensity rather than EAJS meridional location are responsible for changes in TC genesis on an interdecadal time scale. Corresponding to a weaker EAJS, anomalous Rossby wave energy at upper levels displays equatorward propagation at midlatitudes and poleward propagation in the subtropics. This induces anomalous convergence and divergence of wave activity fluxes in East Asia around 30 °N and the SCS, respectively. The anomalous divergence of wave activity fluxes reduces easterlies at upper levels over the SCS, which is favorable to TC genesis.

Influence of Tropical Western Pacific Warm Pool Thermal State on the Interdecadal Change of the Onset of the South China Sea Summer Monsoon in the Late-1990s

An interdecadal shift in the onset date of the South China Sea summer monsoon(SCSSM) is identified during the late 1990 s by using the European Centre for Medium-Range Weather Forecasts Interim Reanalysis dataset. The mean onset date was brought forward by two pentads during 1999–2013 compared to that during 1979–1998. The large-scale atmospheric and oceanic change associated with this shift exhibits a significant interdecadal variation signal around 1998/1999, indicating that the shift during the late 1990 s is robust. Different from the well-known mid-1990 s shift, this shift carried more important systematical significance. Diagnostic analysis suggests that the earlier outbreak of the SCSSM was due to the interdecadal warming of the warm pool, which brought stronger convection anomalies and led to a weak western Pacific subtropical high(WPSH) during boreal spring(March–May). The earlier retreat of the WPSH was a direct cause of this shift.

WINTERTIME MIDDLE EAST SUBTROPICAL WESTERLY JET STREAM INTERANNUAL VARIATION CHARACTERISTICS AND ITS POSSIBLE PHYSICAL FACTORS

Using National Centers for Environmental Prediction/Department of Energy(NCEP/DOE) monthly reanalysis data and an extended reconstruction of the sea surface temperature data provided by National Oceanic and Atmospheric Administration, the basic characteristics of the interannual variation in the wintertime Middle East subtropical westerly jet stream(MEJ) and its possible physical factors are studied. The results show that the climatological mean MEJ axis extends southwestward-northeastward and that its center lies in the northwest part of the Arabian Peninsula. The south-north shift of the MEJ axis and its intensity show obvious interannual variations that are closely related to the ElNio-Southern Oscillation(ENSO) and the mid-high latitude atmospheric circulation. The zonal symmetric response of the Asian jet to the ENSO-related tropical convective forcing causes the MEJ axis shift, and the Arctic Oscillation(AO)causes the middle-western MEJ axis shift. Due to the influences of both the zonal symmetric response of the Asian jet to the ENSO-related tropical convective forcing and the dynamical role of the AO, an east-west out-of-phase MEJ axis shift is observed. Furthermore, the zonal asymmetric response to the ENSO-related tropical convective forcing can lead to an anomalous Mediterranean convergence(MC) in the high troposphere. The MC anomaly excites a zonal wave train along the Afro-Asian jet, which causes the middle-western MEJ axis shift. Under the effects of both the zonal symmetric response to the ENSO-related tropical convective forcing and the wave train along the Afro-Asian jet excited by the MC anomaly, an east-west in-phase MEJ axis shift pattern is expressed. Finally, the AO affects the MEJ intensity, whereas the East Atlantic(EA) teleconnection influences the middle-western MEJ intensity. Under the dynamical roles of the AO and EA, the change in the MEJ intensity is demonstrated.

IMPACT OF THE HEATING OVER SOUTH ASIA UPON THE SUBTROPICAL HIGH OVER WEST-PACIFIC

A case is reported, during which the Subtropical High over the Western Pacific (hereafter, SHWP in abbreviation) shifted northwestward and met-yu at Chaniiang River valley ended. Several numerical experiments onSHWP activity influenced by the heating over south Asia monsoon area are carried out, and the statistic significance of the results is checked. The results indicate that the enhancement of positive heating over South Asia willmotivate a wave-like series of anomaly centers, which propagate northeastward from the maximum heating center.so that a strong positive potential height anomaly center will set up from North China to Japan at Day X resultingin the enhancement of SHWP. Comparison of the influence upon SHWP by the heating over south Asia monsoonarea with that over ITCZ area south to SHWP is also carried out. It is pointed out that the heating over South Asiamonsoon area tends to favor SHWP north\vard movement while the heating over ITCZ area tends to thvor SHWPwestward stretching. As for the time to begin to influence on SHWP, the heating over south Asia monsoon areafavors the enhancement of SHWP atter Day 3 while that over ITCZ south to SHWP effects atter Day 5.

Characteristics of South Asia High in Summer in 2010 and Its Relationship with Rainbands in China

The characteristics of the South Asia high (SAH) and subtropical westerly jets in the summer of 2010 and their relationship with the changes in rainband in China were analyzed. As shown by the results, the SAH in the upper troposphere extended northward relatively late in June 2010. Correspondingly, the subtropical westerly jets on the north side of the SAH jumped northward comparatively late, thus delaying the formation of a strong divergence field in the upper air over the Yangtze-Huaihe River valley. This was one of the main causes for the late onset of plum rains in the Yangtze-Huaihe River valley. In July, there was a vertical structure consisting of upper-level divergence and low-level convergence near the subtropical westerly jets on the north side of the SAH and in the air stream dispersal area on the northeast side of the eastward-extending SAH, which was the dynamic mechanism bringing about frequent and extremely heavy rainstorms during the plum rain period in this year. The SAH in the upper troposphere affected the subtropical high in the lower stratosphere, and thereby led to changes in the main rainband location in China.

A WAVELET PACKET ENERGY DIAGNOSIS OF SOUTH ASIAN SUMMER MONSOON INFLUENCING ON THE WEST PACIFIC SUBTROPICAL HIGH

Based on the wavelet packet decomposition/reconstruction method and the NCEP/NCAR daily reanalysis data set, the relation between the south Asian summer monsoon and the west Pacific subtropical high seasonal variation was discussed, and a corresponding summer monsoon frequency-band energy criterion was defined and introduced for diagnosing the west Pacific subtropical high. Besides, some existing characteristics and rules about the west Pacific subtropical high were further argued and proofed, a few new phenomena and correlation between the south Asian summer monsoon and the west Pacific subtropical high were also revealed and presented.

Cold tolerance of subtropical Porites lutea from the northern South China Sea

Marginal scleractinian corals growing at their latitudinal limits should be quite sensitive to variations in winter sea surface temperatures(SSTs). An extreme cold event occurring in early 2008 offered a unique opportunity to examine the effect of cold-water anomalies on Porites lutea corals and their physiological tolerance and acclimation in the subtropical northern South China Sea(NSCS). Besides in-situ observation, a subsequent aquarium-based experiment was designed for reproducing the chilling process and a 50-year-long Sr/Ca ratio profile from two P. lutea skeletal slabs was analyzed for reconstructed the historical annual minimum SSTs which ceased Porites calcification. The 2008 low-temperature anomaly caused the minimum daily mean SSTs dropped below 13°C in the Daya Bay. The stress symptoms displayed by local P. lutea colonies included polyp retraction, reduced coloration and pale, but none showed tissue sloughing. The ability of P. lutea to survive implied its tolerance of extreme low temperatures. Here we suggest a model on the tolerance of high-latitude Porites under low-temperature stresses, which is when SSTs drop below 18°C, Porites corals contract their tentacles(losing heterotrophic capability), then cease calcification(reducing energy consumption), and meanwhile maintain relatively high levels of zooxanthellae density(sustaining host’s life via photosynthetic capacity of symbiotic zooxanthellae). This study revealed remarkable acclimatization of P. lutea corals to low temperature extremes. This acclimatization is beneficial for Porites corals in the NSCS to expand their living ranges towards the higher-latitude areas and have the potential to be the incipient reef former.

SUBTROPICAL HIGH, LATENT HEATING BY CONVECTION AND ASSOCIATION WITH DISSIPATION AND MAINTENANCE OF SOUTH CHINA SEA TYPHOONS

Numerical modeling and experiments are conducted for the South China Sea typhoons Helen (1995) and Willie (1996) with an auto-adaptive mesh model. It is shown that durating the stage of dissipation the typhoons are mainly related with the subtropical high rather than the topography. The high is sensitive to the intensity change of the typhoon so that the former weakens as the latter strengthens and vice versa. Maintaining the typhoon as a main factor, the release of latent heat is in reversed proportion with the subtropical high in terms of the intensity. It is found that the storm tends to be maintained if it moves close to the westerly trough after landfall.

Circulation Patterns Linked to the Positive Sub-Tropical Indian Ocean Dipole

The positive phase of the subtropical Indian Ocean dipole(SIOD)is one of the climatic modes in the subtropical southern Indian Ocean that influences the austral summer inter-annual rainfall variability in parts of southern Africa.This paper examines austral summer rain-bearing circulation types(CTs)in Africa south of the equator that are related to the positive SIOD and the dynamics through which specific rainfall regions in southern Africa can be influenced by this relationship.Four austral summer rain-bearing CTs were obtained.Among the four CTs,the CT that featured(i)enhanced cyclonic activity in the southwest Indian Ocean;(ii)positive widespread rainfall anomaly in the southwest Indian Ocean;and(iii)low-level convergence of moisture fluxes from the tropical South Atlantic Ocean,tropical Indian Ocean,and the southwest Indian Ocean,over the south-central landmass of Africa,was found to be related to the positive SIOD climatic mode.The relationship also implies that positive SIOD can be expected to increase the amplitude and frequency of occurrence of the aforementioned CT.The linkage between the CT related to the positive SIOD and austral summer homogeneous regions of rainfall anomalies in Africa south of the equator showed that it is the principal CT that is related to the inter-annual rainfall variability of the south-central regions of Africa,where the SIOD is already known to significantly influence its rainfall variability.Hence,through the large-scale patterns of atmospheric circulation associated with the CT,the SIOD can influence the spatial distribution and intensity of rainfall over the preferred landmass through enhanced moisture convergence.

A DIAGNOSTIC ANALYSIS OF THE WEAKENING OF WEST PACIFIC SUBTROPICAL ANTICYCLONE DURING THE PERIOD OF SOUTH CHINA SEA SUMMER MONSOON ONSET IN 1998

The onset of South China Sea summer monsoon in 1998 occurred on May 21st. Using the U.S. National Centers for Environmental Prediction reanalysis data, this paper examines the physical process of the weakening of a subtropical anticyclone in West Pacific during the onset period using the Zwack-Okossi vorticity equation. Results show that during the pre-onset period, the positive vorticity advection in front of an upper tropospheric trough was the most dominant physical mechanism for the increase of the cyclonic vorticity on the 850-hPa layer over the South China Sea and its nearby region. The secondary contribution to the increase of the cyclonic vorticity was the warm-air advection. After the onset, the magnitude of the latent-heat warming term rapidly increased and its effect on the increase of the cyclonic vorticity was about the same as the positive-vorticity advection. The adiabatic term and divergence term contributed negatively to the increase of the cyclonic vorticity most of the time. Thus, the positive vorticity advection is the most important physical mechanism for the weakening of the West Pacific subtropical anticyclone over the South China Sea during the onset period.