Effects of Summer Tropical Convection on Rainfall of Yangtze Valley and Huaihe River Basin

By NCEP/NCAR monthly mean reanalysis data including OLR,500 hPa geopotential height field and so on,effects of summer tropical convection on the location and intensity variation of Western Pacific subtropical high,rainfall of Yangtze valley and Huaihe River basin were studied by using correlation analysis,synthesis analysis.In summer,when the convective activities are intensified (weakened) from the areas around Philippines to Indo-China Peninsula through South China Sea,the Western Pacific subtropical high may shift northward (southward).What's more,the Western Pacific subtropical high has obvious abrupt shifts or unobvious abrupt shifts in the end of June and early July during its northward advance.It affected the stagnation time of East Asia monsoon rain-belt in the Yangtze valley and Huaihe River basin,and caused that the rainfall of this zone was below or above normal.

NATURE OF PRECIPITATION AND ACTIVITY OF CUMULUS CONVECTION DURING THE 1991 MEIYU SEASON OF CHANGJIANG-HUAIHE RIVER BASIN

Seasonal variability regarding the nature of precipitation and the activity of cumulus convection during the 1991 Meiyu season of Changjiang-Huaihe River Basin(Jianghuai)has been investigated by calculating apparent heat source/apparent moisture sink and analyzing TBB(cloud-top blackbody radiation temperature)data.It is found that three periods of strong ascending motion during the Meiyu season lead to three episodes of heavy rain,and the latent heat due to the precipitation is of the sole heat source of the atmosphere.The nature of precipitation shows distinct seasonal variability,from frontal precipitation of the first episode to the extremely strong convective precipitation of the third episode.TBB field of East Asia may well reflect not only the intensity of convection and rainfall,but also the movement of rain belt and convection belt.In the whole Meiyu season.convection belt mainly stays in Jianghuai.but may shift within the domain of East Asia.Its locating in Jianghuai or not determines the maintenance or break of Meiyu.In the third episode,the narrow convection belt over Jianghuai is mainly caused by southwest monsoon which takes moist and convective atmosphere from tropical ocean.

Impact of the Thermal State of the Tropical Western Pacific on Onset Date and Process of the South China Sea Summer Monsoon

Since the early or late onset of the South China Sea summer monsoon （SCSM） has a large impact on summer monsoon rainfall in East Asia, the mechanism and process of early or late onset of the SCSM are an worthy issue to study. In this paper, the results analyzed by using the observed data show that the onset date and process of the SCSM are closely associated with the thermal state of the tropical western Pacific in spring. When the tropical western Pacific is in a warming state in spring, the western Pacific subtropical high shifts eastward, and twin cyclones are early caused over the Bay of Bengal and Sumatra before the SCSM onset. In this case, the cyclonic circulation located over the Bay of Bengal can be early intensified and become into a strong trough. Thus, the westerly flow and convective activity can be intensified over Sumatra, the Indo-China Peninsula and the South China Sea （SCS） in mid-May. This leads to early onset of the SCSM. In contrast, when the tropical western Pacific is in a cooling state, the western Pacific subtropical high anomalously shifts westward, the twin cyclones located over the equatorial eastern Indian Ocean and Sumatra are weakened, and the twin anomaly anticyclones appear over these regions from late April to mid-May. Thus, the westerly flow and convective activity cannot be early intensified over the Indo-China Peninsula and the SCS. Only when the western Pacific subtropical high moves eastward, the weak trough located over the Bay of Bengal can be intensified and become into a strong trough, the strong southwesterly wind and convective activity can be intensified over the Indo-China Peninsula and the SCS in late May. Thus, this leads to late onset of the SCSM. Moreover, in this paper, the influencing mechanism of the thermal state of the tropical western Pacific on the SCSM onset is discussed further from the Walker circulation anomalies in the different thermal states of the tropical western Pacific.

Numerical Simulation of the Relationship between the Anomaly of Subtropical High over East Asia and the Convective Activities in the Western Tropical Pacific

In this paper, a close relationship between the intraseasonal variation of subtropical high over East Asia and the convective activities around the South China Sea and the Philippines is analysed from OLR data.This relationship is studied by using the theory of wave propagating in a slowly varying medium and by using a quasi-geoslrophic, linear, spherical model and the IAP-GCM, respectively. The results show that when the SST is warming around the western tropical Pacific or the Philippines, the convective activities are intensified around the Philippines. As a consequence, the subtropical high will be intensified over East Asia. The computed results also show that when the anomaly of convective activities are caused around the Philippines, a teleconnection pattern of circulation anomalies will be caused over South Asia, East Asia and North America.

Interannual Variability of the Convective Activities Associated with the East Asian Summer Monsoon Obtained from TBBV ariability

In this paper, the interannual variability of the convective activities associated with the East Asian summer monsoon and its association with the thermal distribution of SST anomalies in the tropical Pacific are analyzed by using the daily TBB (Temperature of Black Body at Cloud Top) dataset from 1980 to 1991. The results of composite and individual analyses of TBB anomalies show that the interannual variability of the convective activities associated with the summer monsoon in East Asia is large and has a close relation to the thermal distribution of SST anomalies in the tropical Pacific, especially in the western Pacific warm pool. In the summer with ENSO-like distribution of SST anomalies in the tropical Pacific, the convective activities are weak around the Philippines, then the convective activities are intensified and the summer monsoon rainfall is strong in the area from the Yangtze River basin and the Huaihe River basin in China to Republic of Korea and Japan. On the contrary, in the summer with anti-ENSO-like distribution of SST anomalies in the tropical Pacific, the convective activities are strong around the Philippines, then the convective activities are weakened and the summer monsoon rainfall is weak in the area from the Yangtze River basin and the Huaihe River basin to Republic of Korea and Japan. It may be also found either from the composite analysis or from the individual analysis of TBB anomalies that the convective activities associated with the summer monsoon in East Asia have a good negative relation to that around the Philippines and a positive relation to that over the equatorial central Pacific.

Interactions between the 30－60 Day Oscillation，the Walker Circulation and the Convective Activities in the Tropical Western Pacific and Their Relations to the Interannual Oscillation

In this paper, interactions between the 30-60 day oscillation, the Walker circulation and the convective activitiesin the tropical western Pacific during the Northern Hemisphere summer are analyzed by using the observed data ofwind fields and high-cloud amounts for the period from 1980 to 1989.The analyzed results show that the 30-60 day oscillation (hereafter called LFO) may be largely affected by theconvective activities in the tropical western Pacific. The LFO in the tropical western Pacific during the strongconvective activities around the Philippines stronger than those during the weak convective activities around thePhilippines. Moreover. in the case of strong convective activities around the Philippines, the LFO in the tropical western Pacific and tropical eastern Indian Ocean generally propagates westward, and it is intensified by the LFO with awestward propagating center of maximum oscillation trom the east to 140°E. However, in the case of weakconvective activities around the Philippines, the LFO gradually becomes stronger with a eastward propagating centerof maximum oscillation from the eastern Indian Ocean to the tropical western Pacific.Corresponding to the 30-60 day oscillation, the Walker circulation is also in oscillation over the tropical Pacificand its circulation cell seems to shift gradually westward from the tropical western Pacific to the tropical eastern Indian Ocean with strong convective activities around the Philippines. This may maintain the intensitication ofconvective activities there. However, during the weak convective activities around the Philippines, the Walker circulation gradually moves eastward and an ascending flow may appear in the equatorial central Pacific. This may causeconvective activities to be intensified over the equatorial central Pacific.The analyzed results also show that the LFO in the tropical western Pacific and East Asia may be associated withthe interannual oscillation of the SST anomaly in the tropical western Pacific.

Relationship Between Persistent Heavy Rain Events in the Huaihe River Valley and the Distribution Pattern of Convective Activities in the Tropical Western Pacific Warm Pool

Using daily outgoing long-wave radiation （OLR） data from the National Oceanic and Atmospheric Administration （NOAA） and the National Center for Environmental Prediction/National Center for Atmospheric Research （NCEP/NCAR） reanalysis data of geopotential height fields for 1979-2006, the relationship between persistent heavy rain events （PHREs） in the Huaihe River valley （HRV） and the distribution pattern of convective activity in the tropical western Pacific warm pool （WPWP） is investigated. Based on nine cases of PHREs in the HRV, common characteristics of the West Pacific subtropical high （WPSH） show that the northern edge of the WPSH continues to lie in the HRV and is associated with the persistent ＂north weak south strong＂ distribution pattern of convective activities in the WPWP. Composite analysis of OLR leading the circulation indicates that the response of the WPSH to OLR anomaly patterns lags by about 1-2 days. In order to explain the reason for the effects of the distribution pattern of convective activities in the WPWP on the persistent northern edge of the WPSH in the HRV, four typical persistent heavy and light rain events in the Yangtze River valley （YRV） are contrasted with the PHREs in the HRV. The comparison indicates that when the distribution pattern of the convective activities anomaly behaves in a weak （strong） manner across the whole WPWP, persistent heavy （light） rain tends to occur in the YRV. When the distribution pattern of the convective activities anomaly behaves according to the ＂north weak south strong＂ pattern in the WPWP, persistent heavy rain tends to occur in the HRV. The effects of the ＂north weak south strong＂ distribution pattern of convective activities on PHREs in the HRV are not obvious over the seasonal mean timescale, perhaps due to the non-extreme status of convective activities in the WPWP.

Role of the 10–20-Day Oscillation in Sustained Rainstorms over Hainan,China in October 2010

Hainan,an island province of China in the northern South China Sea,experienced two sustained rainstorms in October 2010,which were the most severe autumn rainstorms of the past 60 years.From August to October 2010,the most dominant signal of Hainan rainfall was the 10-20-day oscillation.This paper examines the roles of the 10-20-day oscillation in the convective activity and atmospheric circulation during the rainstorms of October 2010 over Hainan.During both rainstorms,Hainan was near the center of convective activity and under the influence of a lower-troposphere cyclonic circulation.The convective center was initiated in the west-central tropical Indian Ocean several days prior to the rainstorm in Hainan.The convective center first propagated eastward to the maritime continent,accompanied by the cyclonic circulation,and then moved northward to the northern South China Sea and South China,causing the rainstorms over Hainan.In addition,the westward propagation of convection from the tropical western Pacific to the southern South China Sea,as well as the propagation farther northward,intensified the convective activity over the northern South China Sea and South China during the first rainstorm.

Cloud Radiative Forcing in Asian Monsoon Region Simulated by IPCC AR4 AMIP Models

This study examines cloud radiative forcing （CRF） in the Asian monsoon region （0° 50°N, 60° 150°E） simulated by Intergovernmental Panel on Climate Change （IPCC） Fourth Assessment Report （AR4） AMIP models. During boreal winter, no model realistically reproduces the larger long-wave cloud radiative forcing （LWCF） over the Tibet Plateau （TP） and only a couple of models reasonably capture the larger short-wave CRF （SWCF） to the east of the TP. During boreal summer, there are larger biases for central location and intensity of simulated CRF in active convective regions. The CRF biases are closely related to the rainfall biases in the models. Quantitative analysis further indicates that the correlation between simulated CRF and observations are not high, and that the biases and diversity in SWCF are larger than that in LWCF. The annual cycle of simulated CRF over East Asia （0°-50°N, 100°-145°E） is also examined. Though many models capture the basic annual cycle in tropics, strong LWCF and SWCF to the east of the TP beginning in early spring are underestimated by most models. As a whole, GFDL-CM2.1, MPI-ECHAM5, UKMO-HadGAM1, and MIROC3.2 （medres） perform well for CRF simulation in the Asian monsoon region, and the multi-model ensemble （MME） has improved results over the individual simulations. It is suggested that strengthening the physical parameterizations involved over the TP, and improving cumulus convection processes and model experiment design are crucial to CRF simulation in the Asian monsoon region.

The Possible Influences of the Increasing Anthropogenic Emissions in India on Tropospheric Ozone and OH

A 3-D chemical transport model (OSLO CTM2) is used to investigate the influences of the increasing anthropogenic emission in India. The model is capable of reproducing the observational results of the INDOEX experiment and the measurements in summer over India well. The model results show that when NOx and CO emissions in India are doubled, ozone concentration increases, and global average OH decreases a little. Under the effects of the Indian summer monsoon, NOx and CO in India are efficiently transported into the middle and upper troposphere by the upward current and the convective activities so that the NOX, CO, and ozone in the middle and upper troposphere significantly increase with the increasing NOx and CO emissions. These increases extensively influence a part of Asia, Africa, and Europe, and persist from June to September.

Global Response to Tropical Diabatic Heating Variability in Boreal Winter

Global teleconnections associated with tropical convective activities were investigated, based on monthly data of 29 Northern Hemisphere winters： December, January, February, and March （DJFM）. First, EOF analyses were performed on the outgoing longwave radiation （OLR） data to characterize the convective ac tivity variability in the tropical Indian Ocean and the western Pacific. The first EOF mode of the convective activity was highly correlated with the ENSO. The second EOF mode had an east–west dipole structure, and the third EOF mode had three convective activity centers. Two distinct teleconnection patterns were identified that were associated, respectively, with the second and third EOF modes. A global primitive equation model was used to investigate the physical mechanism that causes the global circulation anoma lies. The model responses to anomalous tropical thermal forcings that mimic the EOF patterns matched the general features of the observed circulation anomalies well, and they were mainly controlled by linear processes. The importance of convective activities in the tropical Indian Ocean and western Pacific to the extended and longrange forecasting capability in the extratropics is discussed.

A CASE STUDY OF THE UNCORRELATED RELATIONSHIP BETWEEN TROPICAL TROPOPAUSE TEMPERATURE ANOMALIES AND STRATOSPHERIC WATER VAPOR ANOMALIES

Using the measurements from the Halogen Occultation Experiment(HALOE)and the European Centre for Medium-Range Weather Forecasts(ECMWF)Interim reanalysis data for the period 1994-2005,we analyzed the relationship between tropical tropopause temperature anomalies and stratospheric water vapor anomalies.It is found that tropical tropopause temperature is correlated with stratospheric water vapor,i.e.,an anomalously high(low)tropical tropopause temperature corresponds to anomalously high(low)stratospheric water vapor during the period 1994-2005,except for 1996.The occurrence frequency and strength of deep convective activity during the‘mismatched'months is less and weaker than that during the‘matched'months in 1996.However,the instantaneous intensity of four short periods of deep convective activity,caused by strong surface cyclones and high sea surface temperatures,are greater during the‘mismatched'months than during the‘matched'months.Water vapor is transported from the lower troposphere to the lower stratosphere through a strong tropical upwelling,leading to an increase in stratospheric water vapor.On the other hand,deep convective activity can lift the tropopause and cool its temperature.In short,the key factor responsible for the poor correlation between tropical tropopause temperature and stratospheric water vapor in1996 is the instantaneous strong deep convective activity.In addition,an anomalously strong Brewer-Dobson circulation brings more water vapor into the stratosphere during the‘mismatched'months in 1996,and this exacerbates the poor correlation between tropical tropopause temperature and stratospheric water vapor.

Simulation of oxygen transfer in liquid lead under influence of nanoparticles by using lattice Boltzmann method

Oxygen transfer presents a serious challenge in the application of liquid lead as a nuclear coolant in advanced reactors. To mitigate corrosion by liquid lead in contact with steel, carefully controlling the oxygen concentration has been used as an effective way. Oxygen needs to mix in liquid lead uniformly and quickly. To enhance oxygen transport in liquid lead, nanoparticles are added to the liquid metal. In the current study, a lattice Boltzmann method is applied to investigate natural convection of copper/lead and aluminum oxide/lead in two-dimensional simplified container. Two thermal boundary cases are evaluated in order to check the effect of different natural convection flow patterns on oxygen transport. Some useful information are obtained such as improvement in natural convection and reduction in oxygen equilibrium time.

THE RELATIONSHIP BETWEEN THE MOVEMENT OF THE MEIYU/BAIU RAIN BELT AND THE PERIODIC NORTHWESTWARD PROPAGATION OF THE CONVECTIVE ACTIVITY FROM TROPICAL WEST PACIFIC

In order to investigate the effect of the factors in tower latitudes on Meiyu/Baiu front,a diagnostic analysis for the two cases during June to July of 1985 and 1986 was examined.We found that (1)when the tropical convective activity moves westward to 10.5-15.5′N/140°E from east side of 10.5-15.5°N/160°E,the northward shifts of the Meiyu/Baiu rain belt occurs;(2)the main factor which results in the northward and southward shifts of Meiyu/Baiu rain belt is thought as the 8,18 and 30 day oscillations of the tropical convective activity around West Pacific. Meanwhile,the wave train propagating from Lake Baikal via Okhotsk Sea to the tropics could sometimes shift Baiu rain belt southward;(3)the onsets of Meiyu in China of both cases tend to take place just when the convective activity around lower latitudes moves westward through about 140°E with the 8,18 and 30 day oscillation periods firstly coming to June.

SEASONAL VARIATIONS OF CONVECTIVE ACTIVITIES OVER THE SOUTH CHINA SEA AND ITS NEIGHBORHOOD AND THEIR COMPARATIVE ANALYSES IN THE STRONG AND WEAK CONVECTION YEARS

The seasonal variations of convective activities over the South China Sea(SCS)and its neighborhood.as well as the similarities and differences of convection in the different key regions during the strong and weak convection years are analyzed by using the pentad data of TBB from 1980 to 1993.The results show that in winter and summer the seasonal variations of the convective activities are synchronous over the SCS and its neighborhood,the anomalous convection amplitudes are obviously different in different regions.The significant extents of convective activities have somewhat seasonal differences in the strong and weak convection years.In the strong convection years,it is in winter,spring and autumn that the convection anomaly is more evident than that in the normal years,however,after the summer monsoon onset the convection is sustained.stable and similar to that in the normal years.In the weak convection years.the convection weakens greatly in each season.but the primary weakening occurs in spring.summer and autumn.No matter in the strong or the weak convection years.the convective activities are somewhat of difference in the Bay of Bengal.the Indochina Peninsula.the SCS and the Philippines.In addition. the convective activities are also different over the south and the north parts of the SCS.the convection variation in the strong year is similar to that in the weak year over the north part of the SCS.but over the south part there are great differences.

THE ROLE OF TROPICAL CONVECTION IN VARIATION OF INTRASEASONAL TELECONNECTIONS OF TROPICAL AND EXTRATROPICAL CIRCULATIONS

Based on ECMWF objective analysis data, the relationships between tropical convective activi- ties and extratropical circulation, as well as the low frequency kinetic energy, have been investigat- ed by making use of diagnostic analysis methods on the intraseasonal time scale in winters of 1983/ 1984 and 1986/1987. From this study, it is found that the different intensities of the tropical con- vective activities may bring about both the different intraseasonal teleconnection wave trains be- tween the tropics and the extratropics and the different dispersions of the low frequency wave ener- gy. Moreover, the tropical convection can be an important junction factor for the teleconnection ef- fect of the tropical and extratropical circulations on the intraseasonal time scale.

Extended-Range Precursors for Summer Consecutive Extreme Rainfall in the Yangtze River Valley Related to Intraseasonal Variations of the Pacific-Japan Teleconnection

In summer,the Yangtze River valley(YRV)in central–eastern China frequently suffers consecutive extreme rainfall(CER)events,causing floods and huge damages.On the daily timescale,our previous study has shown that the Pacific–Japan(PJ)teleconnection is related to the CER events over the YRV,and is a source for long-term(lead time of about 10 days)forecasts of CER events.To facilitate extended-range(lead time of about 20 days)prediction of CER,in the present study,we use the band-pass filter for the PJ teleconnection to keep only the prolonged atmospheric circulation information at the intraseasonal timescale and try to identify more advanced precursors for the CER events over the YRV.Power spectrum analysis was implemented on 9-day sliding mean of the precipitation anomalies.It is found that summer precipitation in YRV has significant 10–40-day oscillations,and the CER events over the YRV are affected by the intraseasonal oscillation(ISO)of the PJ teleconnection.When the ISO of the PJ teleconnection enters its positive phase,it is favorable for CER events to occur.Dynamic diagnoses and model experiments demonstrate that the ISO of the PJ teleconnection is attributed to the intraseasonal convective activities and diabatic heating around the Philippines,which generate significant northward energy dispersion and propagation of Rossby waves up to 16 days prior to occurrences of the CER events in the YRV.The ISO of the PJ teleconnection and the convective activities in the tropical South Asia provide significant and earlier precursors for extended-range forecasts of the CER events along the YRV.

Interannual Variability of Summertime Outgoing Longwave Radiation over the Maritime Continent in Relation to East Asian Summer Monsoon Anomalies

The Maritime Continent（MC） is under influences of both the tropical Pacific and the Indian Ocean. Anomalous convective activities over the MC have significant impacts on the East Asian summer monsoon（EASM） and climate in China. In the present study, the variation in convective activity over the MC in boreal summer and its relationship to EASM anomalies are investigated based on regression analysis of NCEP–NCAR reanalysis and CMAP [Climate Prediction Center（CPC） Merged Analysis of Precipitation] data, with a focus on the impacts of ENSO and the Indian Ocean Dipole（IOD）. The most significant interannual variability of convective activity is found over 10°S–10°N, 95°–145°E, which can be roughly defined as the key area of the MC（hereafter, KMC）. Outgoing longwave radiation anomaly（OLRA） exhibits 3- to 7-yr periodicities over the KMC, and around 70% of the OLRA variance can be explained by the ENSO signal. However, distinct convection and precipitation anomalies still exist over this region after the ENSO and IOD signals are removed. Abnormally low precipitation always corresponds to positive OLRA over the KMC when negative diabatic heating anomalies and anomalous cooling of the atmospheric column lead to abnormal descending motion over this region. Correspondingly, abnormal divergence occurs in the lower troposphere while convergence occurs in the upper troposphere, triggering an East Asia–Pacific/Pacific–Japan（EAP/PJ）-like anomalous wave train that propagates northeastward and leads to a significant positive precipitation anomaly from the Yangtze River valley in China to the islands of Japan. This EAP/PJ-like wave pattern becomes even clearer after the removal of the ENSO signal and the combined effects of ENSO and IOD, suggesting that convective anomalies over the KMC have an important impact on EASM anomalies. The above results provide important clues for the prediction of EASM anomalies and associated summer precipitation anomalies in China.

Contribution of Water Vapor to the Record-Breaking Extreme Meiyu Rainfall along the Yangtze River Valley in 2020

A record-breaking extreme Meiyu rainfall occurred along the Yangtze River valley(YRV)in 2020 since 1961,persisting from 11 June to 31 July with the largest amount and the highest intensity.From the aspect of water vapor,the causes of its formation are revealed in this study.The 2020 Meiyu rainfall amount is directly attributed to the greatly enhanced vertically integrated water vapor transport(IVT)convergence,which is in turn primarily determined by the mean circulation dynamic(MCD)contribution associated with anomalous East Asian summer monsoon(EASM)and the thermodynamic component(TH)contribution due to water vapor anomaly.The MCD contribution is mainly responsible for the extreme Meiyu rainfall amount and abundant water vapor convergence in the YRV,whereas the TH contribution tends to shift Meiyu rain belt northward to the Yangtze-Huaihe River valley,extending the Meiyu rainfall coverage area.Furthermore,the excessive moist static energy(MSE)associated with the largest water vapor anomaly could substantially increase the atmospheric instability,favoring the extreme 2020 Meiyu rainfall intensity.In terms of the tremendous IVT to the YRV from both the South China Sea and Bay of Bengal during the 2020 Meiyu period,the low-level anticyclone anomalies over the western North Pacific(WNP)and Bay of Bengal provide appropriate atmospheric circulation conditions,and they are generated by the super suppressed WNP convective activities as a Matsuno-Gill type response,which are further attributed to the combined warm SST anomalies in both the tropical western Indian Ocean(TWIO)and tropical Atlantic Ocean(TAO)eventually.

Effect of Active Gas on Weld Shape and Microstructure of Advanced A-TIG-Welded Stainless Steel

Advanced A-TIG method was conducted to increase the weld penetration and compared with the conventional TIG welding process.A two-pipeline setup was designed to apply Ar ＋ CO_2 mixed gas as the outer layer,while pure argon was applied as the inner layer to prevent any consumption of the tungsten electrode.The results indicate that the presence of active gas in the molten pool led to the change in the temperature coefficient of surface tension so that the Marangoni convection turns inward and forms a deep weld zone.The increase in gas flow rate causes a decrease in the weld efficiency which is attributed to the increase in oxygen content in the weld pool and the formation o f a thicker oxide layer on the weld surface.Moreover,the stir and the temperature fluctuation,led by double shielding gas,create more homogeneous nucleation sites in the molten pool so that a fine grain micros true ture was obtained.