Impact of the Western Pacific Tropical Easterly Jet on Tropical Cyclone Genesis Frequency over the Western North Pacific

Although it is well known that the tropical easterly jet(TEJ)has a significant impact on summer weather and climate over India and Africa,whether the TEJ exerts an important impact on tropical cyclone(TC)activity over the western North Pacific(WNP)remains unknown.In this study,we examined the impact of the TEJ on the interannual variability of TC genesis frequency over the WNP in the TC season(June-September)during 1980-2020.The results show a significant positive correlation between TC genesis frequency over the WNP and the jet intensity in the entrance region of the TEJ over the tropical western Pacific(in brief WP_TEJ),with a correlation coefficient as high as 0.66.The intensified WP_TEJ results in strong ageostrophic northerly winds in the entrance region and thus upper-level divergence to the north of the jet axis over the main TC genesis region in the WNP.This would lead to an increase in upward motion in the troposphere with enhanced low-level convergence,which are the most important factors to the increases in low-level vorticity,mid-level humidity and low-level eddy kinetic energy,and the decreases in sea level pressure and vertical wind shear in the region.All these changes are favorable for TC genesis over the WNP and vice versa.Further analyses indicate that the interannual variability of the WP_TEJ intensity is likely to be linked to the local diabatic heating over the Indian Ocean-western Pacific and the central Pacific El Ni?o-Southern Oscillation.

STRUCTURAL AND EVOLUTION CHARACTERISTICS OF THE EASTERLY VORTEX OVER THE TROPICAL REGION

By employing the NCEP/NCAR reanalysis data sets (1000-10hPa, 2.5°× 2.5°), the characteristics have been analyzed of the structure and evolution of an easterly vortex over the tropical upper troposphere relating to the east-west direction shift of the subtropical anticyclone over the Western Pacific Ocean. It is shown that there exists a westward shift simultaneously between the anticyclone and the vortex locating south of it. The anticyclone retreats eastward abnormally while the easterly encounters with the westerly around the same longitudes as they move from the opposite directions. The former is an upper weather system, extending from mid-troposphere to the height of 50 hPa with the center locating on 200 hPa. The vertical thermal distribution illustrates the characteristics of being"warm in the upper layer but cold in the lower layer". The divergence effect and the vertical motion change largely within the east and west sides of the easterly vortex and ascending branch transforms to descending branch near its center.

Climatic Study on the Summer Tropical Easterly Jet at 200 hPa

The low latitude easterlies at 200 hPa in summer (May-October) is analysed climatically during the 13-year period from 1968 to 1980, with a special emphasis on the relationships between the anomalous tropical easterly jet Stream over South Asia and the low latitude atmospheric circulation, and also the summer monsoon precipitation in India. The compositing analysis shows that the tropical easterly jet stream over South Asia has five anomalous patterns at 200 hPa i.e. the western pattern, middle pattern, eastern pattern, two-branch pattern and multi-core pattern. Evidence has shown that the precipitaion in India anomalously increased during the anomalous period of the western pattern and the middle pattern, but reverse case is true in the eastern pattern. Some different anomalies of the precipitation in different area of India were found during the other two anomalous pattern.

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.

Mean Kinematic Characteristics of Synoptic Easterly Disturbances over the Atlantic

This study investigates the mean kinematic characteristics of the tropical Atlantic easterly disturbances in January-March （JFM）, April-June （AM J）, July-September （JAS） and October-December （OND） from 1968-1998. For each season, the preferential tracks of these disturbances in the 3--10-day band periods were computed and spatialized, as well as their associated wavelength, velocity and main period, which lies between 3-5 days and between 6-9 days depending on the track and the season. Two main tracks are highlighted over the Atlantic Ocean. During OND and JFM these two tracks are well separated and located in each hemisphere around 15°S and 12.5°N. From AMJ to JAS these tracks migrate northward; in JAS, they merge into one over the northern tropical Atlantic along 17.5°N. The associated wavelength fields exhibit a meridional gradient, with large wavelengths （greater than 4000 km） around the equator, between 5°N and 5°S, and smaller wavelengths outside of this latitude band （between 2500-3500 kin）. The phase speed is also found to exhibit poleward decreasing values from 12-6 m s^-1. Over the north Atlantic track, 6-9-day disturbances were found to occur from January to May and approximately from October to December. From June to September, the 3-5-day waves dominate the synoptic activity. Over the south Atlantic track, between May and August the synoptic variability is mainly explained by the 3-5-day disturbances but from January to April and from September to December both 3-5-day waves and 6-9-day waves can occur.

Cause Analysis of a Double-cyclone Type of Rainstorm Process with Easterly Wave

On the basis of comprehensive analysis on weather background and main influencing system of rainstorm formation,using NCEP reanalysis data,rainfall data of Shaoyang ground regional automatic station,a new generation of Doppler weather radar product information,etc.,high-altitude weather situation and physical formation mechanism of local double-cyclone type of rainstorm process with easterly wave in Shaoyang area on August 14,2016 were analyzed in detail,to find out prophase signal features which had indicating significance for rainstorm forecast. The results showed that:(1) the position of zonal subtropical high pressure in east-west direction was the necessary condition for the formation of easterly wave.(2) The rainstorm formation was closely related to double tropical depressions acting in the south of subtropical high pressure,and westward movement of easterly wave over 500 hPa and low-pressure inverted trough at low layer were main impact systems of the rainstorm.(3) Continuous flow of water vapor from the South China Sea to northwest was the source of water vapor required by this rainstorm.(4) Numerical prediction model products had certain guiding significance for forecasting the heavy precipitation,with important reference value.(5) Doppler radar products had strong forecasting ability in the nowcasting of rainstorm falling zone,which was an important measure of correcting forecast errors.

The effects of the intertropical convergence zone on the easterly jet stream during Northern summer

In this paper, a strong 1TCZ process and an 1TCZ - absent process during FGGE in 1979 were selected for comparison to explore how they were subject to the influence of the evolution of the upper easterly jets.

Analysis on an Easterly Wave Thunderstorm and Gale Weather during the Latter Flood Season of 2010

[Objective] The research aimed to analyze an easterly wave thunderstorm and gale weather during the latter flood season of 2010.[Method] Based on conventional observation data,data of automatic station,NCEP 1°×1° reanalysis data,Doppler radar reflectivity and radial velocity data,the easterly wave thunderstorm and gale weather process which happened during 4-5 August,2010 was analyzed.The circulation situation,wind field and dynamic & thermal structures of easterly wave,echo characteristics of Doppler radar when thunderstorm and gale happened were studied.[Result] The thunderstorm and gale weather happened in the northeaster zone in front of the deep thick easterly wave trough.When thunderstorm and gale weather happened,position of the subtropical high was by north(ridge line was at 35° N).Eastward movement of the north branch of trough compelled subtropical high splitting into east and west circles.Westward extension of the east subtropical high and saddle-type field circulation were favorable for generation and development of the easterly wave.As development and westward movement of the easterly wave,in the influence zone in front of the trough,upper easterly component transmitted downward.Then,low-level northeaster obviously strengthened,and thunderstorm and gale weather appeared.In the zone where thunderstorm and gale happened,airflow had cyclonic convergence at the middle and low layers and anti-cyclonic divergence near the ground layer.Subsidence movement was obvious.Moreover,thermal force structure that it tended to be dry and cold at the middle and high layers,warm and wet at the low layer existed.Supercell storm was at the developed stage on 4th.It had obvious mesocyclone and hooked echo characteristics(meso-and small-scale characteristics).Characteristics of the squall line,gale region and adverse wind region appeared in central west Guangdong on 5th.Doppler characteristics of the mesocyclone,hooked echo,squall line,gale region and adverse wind region had indication significance for short-imminent forecast of the thunderstorm and gale.[Conclusion] This research revealed some information which had significance for forecasting local easterly wave thunderstorm and gale weather.

Characteristics of Soliton with Dynamic Constraints on its Existence/Propagation in Tropical Easterly Wave

The study concerns the propagation of easterly wave (EW) at tropics as west-moving soliton more steady both in ionn and velocity as evidenced in the dynamic framework.Under the impact of different circulation patterns over the regions of western Pacific trade wind,South-Asia monsoon and their transition,such a soliton becomes tapering off during its westward movement and degrading to a common dispersive wave on the whole,followed by dismtegra-non when striking the South-China Sea monsoon segment,thereby indicating that the sea sector is inaccessible to the soliton When no monsoon trough is present over the South Asian monsoon area around 30癗 or the monsoon depression ]S shallow,it is likely to have west-travelling soliton,which suggests the incursion of the EW into the South-Asian monsoon region.

An Easterly Wave Generated Heavy Rainfall Event over South India—A Case Study

Easterly waves are one of the rain-bearing systems of northeast monsoon and produce massive rainfall events over south India. In the present case study, an attempt is made to identify extreme heavy rainfall event over south India on 26th October, 2006 due to the passage of the easterly wave. Satellite images provide an inverted v-shape easterly wave. Next, circulation features at different levels clearly indicate the location, movement and speed of the easterly wave. Strong north-easterlies with a magnitude of 9.9 m/s are maintained at the surface. The convergence is mainly occupied between 12°N - 16°N, while the divergence is 5°N - 12°N on 26th October, 2006 at the surface level. On 25th, easterly wave is advected north of trough with a magnitude of 0.2 m/s and increased during the remaining days. There are two divergence cells along 5°N and 16°N before and after the event at 700 hPa level. Thus this study helps to bring out the essential characteristics of the easterly wave during northeast monsoon. The highlight of this study is that the easterly wave creates floods in the absence of tropical cyclones over south India.

Oscillation of Surface PM2.5 Concentration Resulting from an Alternation of Easterly and Southerly Winds in Beijing： Mechanisms and Implications

We used simultaneous measurements of surface PM_（2.5） concentration and vertical profiles of aerosol concentration,temperature, and humidity, together with regional air quality model simulations, to study an episode of aerosol pollution in Beijing from 15 to 19 November 2016. The potential effects of easterly and southerly winds on the surface concentrations and vertical profiles of the PM_（2.5） pollution were investigated. Favorable easterly winds produced strong upward motion and were able to transport the PM_（2.5） pollution at the surface to the upper levels of the atmosphere. The amount of surface PM_（2.5） pollution transported by the easterly winds was determined by the strength and height of the upward motion produced by the easterly winds and the initial height of the upward wind. A greater amount of PM_（2.5） pollution was transported to upper levels of the atmosphere by upward winds with a lower initial height. The pollutants were diluted by easterly winds from clean ocean air masses. The inversion layer was destroyed by the easterly winds and the surface pollutants and warm air masses were then lifted to the upper levels of the atmosphere, where they re-established a multi-layer inversion. This region of inversion was strengthened by the southerly winds, increasing the severity of pollution. A vortex was produced by southerly winds that led to the convergence of air along the Taihang Mountains. Pollutants were transported from southern–central Hebei Province to Beijing in the boundary layer. Warm advection associated with the southerly winds intensified the inversion produced by the easterly winds and a more stable boundary layer was formed. The layer with high PM_（2.5） concentration became dee-per with persistent southerly winds of a certain depth. The polluted air masses then rose over the northern Taihang Mountains to the northern mountainous regions of Hebei Province.

Controls on the Northward Movement of the ITCZ over the South China Sea in Autumn:A Heavy Rain Case Study

The autumn Intertropical Convergence Zone(ITCZ)over the South China Sea(SCS)is typically held south of 10°N by prevailing northeasterly and weakening southwesterly winds.However,the ITCZ can move north,resulting in heavy rainfall in the northern SCS(NSCS).We investigate the mechanisms that drove the northward movement of the ITCZ and led to heavy non-tropical-cyclone rainfall over the NSCS in autumn of 2010.The results show that the rapid northward movement of the ITCZ on 1 and 2 October was caused by the joint influence of the equatorial easterlies(EE),southwesterly winds,and the easterly jet(EJ)in the NSCS.A high pressure center on the east side of Australia,strengthened by the quasi-biweekly oscillation and strong Walker circulation,was responsible for the EE to intensify and reach the SCS.The EE finally turned southeast and together with enhanced southwesterly winds associated with an anticyclone,pushed the ITCZ north.Meanwhile,the continental high moved east,which reduced the area of the EJ in the NSCS and made room for the ITCZ.Further regression analysis showed that the reduced area of the EJ and increased strength of the EE contributed significantly to the northward movement of the ITCZ.The enhancement of the EE preceded the northward movement of the ITCZ by six hours and pushed the ITCZ continually north.As the ITCZ approached 12°N,it not only transported warm moist air but also strengthened the dynamic field by transporting the positive vorticity horizontally and vertically which further contributed to the heavy rainfall.

一种基于混沌的软件水印算法框架及实现

针对现有软件水印算法中存在的一些不足,将反逆向工程技术和混沌系统与Easter Egg软件水印的思想相结合,提出了一个基于混沌的软件水印算法框架.该框架通过引入混沌系统,把水印信息散列编码到整个代码当中,以保护全部代码;通过引入反逆向工程技术来抵抗逆向工程攻击,算法框架与软硬件平台无关.在i386体系结构Windows平台下实现了该算法框架,并以该实现为例分析了水印的鲁棒性,讨论了水印的嵌入对程序性能的影响.分析表明,该算法可以有效地抵抗各种语义保持变换攻击,对逆向工程攻击具有较好的抵抗性,鲁棒性较高.

Influence of Sea Level Pressure on Inter-Annual Rainfall Variability in Northern Senegal in the Context of Climate Change

This study examines the inter-annual variability of rainfall and Mean Sea Level Pressure (MSLP) over west Africa based on analysis of the Global Precipitation Climatology Project (GPCP) and National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis respectively. An interconnection is found in this region, between Mean Sea Level Pressure (MSLP) anomaly (over Azores and St. Helena High) and monthly mean precipitation during summer (June to September: JJAS). We also found that over northern Senegal (15°N - 17°N;17°W - 13°W) the SLP to the north is strong;the wind converges at 200 hPa corresponding to the position of the African Easterly Jet (AEJ) the rotational wind 700 hPa (corresponding to the position of the African Easterly Jet (AEJ) coming from the north-east is negative. In this region, the precipitation is related to the SLP to the north with the opposite sign. The Empirical Orthogonal Functions (EOF) of SLP is also presented, including the mean spectrum of precipitation and pressures to the north (15°N - 40°N and 50°W - 25°W) and south (40°S - 10°S and 40°W - 0°E). The dominant EOF of Sea Level Pressures north and south of the Atlantic Ocean for GPCP represents about 62.2% and 69.4% of the variance, respectively. The second and third EOFs of the pressure to the north account for 24.0% and 6.5% respectively. The second and third EOFs of the pressure to the south represent 12.5% and 8.9% respectively. Wet years in the north of Senegal were associated with anomalous low-pressure areas over the north Atlantic Ocean as opposed to the dry years which exhibited an anomalous high-pressure area in the same region. On the other hand, over the South Atlantic, an opposition is noted. The wavelet analysis method is applied to the SLP showings to the north, south and precipitation in our study area. The indices prove to be very consistent, especially during intervals of high variance.

The Impact of Warm Pool SST and General Circulation on Increased Temperature over the Tibetan Plateau

In this paper, the possible reason of Tibetan Plateau （TP） temperature increasing was investigated. An increase in T min （minimum temperature） plays a robust role in increased TP temperature, which is strongly related to SST over the warm pool of the western Pacific Ocean, the subtropical westerly jet stream （SWJ）, and the tropical easterly upper jet stream （TEJ）, and the 200hPa zonal wind in East Asia. Composite analysis of the effects of SST, SWJ, and TEJ on pre and postabrupt changes in T a （annual temperature） and T min over the TP shows remarkable differences in SST, SWJ, and TEJ. A lag correlation between T a /T min , SST, and SWJ/TEJ shows that changes in SST occur ahead of changes in T a /T min by approximately one to three seasons. Partial correlations between T a /T min , SST, and SWJ/TEJ show that the effect of SWJ on T a /T min is more significant than the effect of SST. Furthermore, simulations with a community atmospheric model （CAM3.0） were performed, showing a remarkable increase in T a over the TP when the SST increased by 0.5 ？ C. The main increase in T a and T min in the TP can be attributed to changes in SWJ. A possible mechanism is that changes in SST force the TEJ to weaken, move south, and lead to increased SWJ and movement of SWJ northward. Finally, changes in the intensity and location of the SWJ cause an increase in T a /T min . It appears that TP warming is governed primarily by coherent TEJ and SWJ variations that act as the atmospheric bridges to remote SSTs in warmpool forcing.

STUDY OF DOUBLE RAIN BANDS IN A PERSISTENT RAINSTORM OVER SOUTH CHINA

Using the U.S. National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data at 1°× 1° o resolution, analysis is performed on a persistent heavy rainfall event with two rain bands to the south of the Yangtze River during 17-22 June 2005. The northern rain band was related to the atmospheric mass adjustment of cold front precipitation and the associated ageostrophic feature to the rear right of subtropical westerly jets, while the southern counterpart formed under the joint influence of easterly/westerly jets and the South Asian high （SAH）. The ageostrophic wind field to the rear right of the easterly jet center gives rise to an anti-circulation that favors the genesis of the southern belt. The feature ofdu/dt 〈0 around the SAH ridge line and to the rear right of the easterly jet streak results in a strong v - vg〈O field in the vicinity of the rain region as well as to its south. When westerly jets move southward, an intense v Vg〉0 feature appears to the north of the rain region, i.e., behind the center of the westerly jets. The associated mass adjustment leads to vigorous divergence over the rain region, which is responsible for the strong precipitation from the warm sector of the front. Also, a θe front at the middle level of the southern rain band and the cold front favor the release of instable energy to enhance the rainstorm. The southern and northern fronts approach each other and the two rain belts merge into one.

QBO Features of Tropical Pacific wind Stress Field with the Relation to El Nino

Analysis has been implemented of 1970-1992 tropical Pacific wind stress anomaly and sea surface temperature anomaly (SSTA) datasets, indicating that quasi-biennial oscillation (QBO) of the tropical Pacific WS and SSTA is featured both by a standing and a progressive form, the former emerging in the most intense centers of action and the latter travelling east- or west-ward out of the SSTA sources. Results show that the SSTA is in the warm (cold) phase as zonal component of euqatorial wind stress anomaly gets weakened (reinforced) and the QBO of wind stress anomaly is well related to the El Nino cycle.

Bias Analysis in the Simulation of the Western North Pacific Tropical Cyclone Characteristics by Two High-Resolution Global Atmospheric Models

This study compares the atmosphere-only HighResMIP simulations from FGOALS-f3-H(FGOALS)and MRIAGCM3-2-S(MRI)with respect to tropical cyclone(TC)characteristics over the Western North Pacific(WNP)for the July-October months of 1985-2014.The focus is on investigating the role of the tropical easterly jet over the Western Pacific(WP_TEJ)in modulating the simulation biases in terms of their climatological distribution and interannual variability of WNP TC genesis frequency(TCGF)based on the analysis of the genesis potential index(GPI).Results show that the two models reasonably capture the main TC genesis location,the maximum center of frequency,and track density;however,their biases mainly lie in simulating the intense TCs and TCGF distributions.The MRI better simulates the windpressure relationship(WPR)but overestimates the proportion of super typhoons(SSTYs).At the same time,FGOALS underestimates the WPR and the proportion of SSTYs but better simulates the total WNP TC precipitation.In particular,FGOALS overestimates the TCGF in the northeastern WNP,which is strongly tied to an overestimated WP_TEJ and the enhanced vertical circulation to the north of its entrance region.In contrast,the MRI simulates a weaker WP_TEJ and vertical circulation,leading to a negative TCGF bias in most of the WNP.Both models exhibit comparable capability in simulating the interannual variability of WP_TEJ intensity,but the composite difference of large-scale atmospheric factors between strong and weak WP_TEJ years is overestimated,resulting in larger interannual anomalies of WNP TCGF,especially for FGOALS.Therefore,accurate simulations of the WP_TEJ and the associated oceanic and atmospheric factors are crucial to further improving WNP TC simulations for both models.

Diagnosis of a Severe Rainstorm Event Induced by Eastly Wave and Vortex in Off Southeast Coast of China

Using the NCEP reanalysis at 1°×1° resolution in conjunction with satellite imagery,a study is undertaken of easterly wave related rainstorm events on August 3~4,2001 in seaboards between northern Fujian and southern Zhejiang,expounding the scheme for computing helicity,and exploring the rainstorm evolution and the genesis of the Yandang mountains-triggered a meso-vortex(Duan and Chen,2005) by means of helicity and Q vector divergence.Besides,MM5V2 is employed to simulate the easterly wave caused meso-vorte...

Contrasting Regional Responses of Indian Summer Monsoon Rainfall to Exhausted Spring and Concurrently Emerging Summer El Nino Events

The inverse relationship between the warm phase of the El Nino Southern Oscillation(ENSO)and the Indian Summer Monsoon Rainfall(ISMR)is well established.Yet,some El Nino events that occur in the early months of the year(boreal spring)transform into a neutral phase before the start of summer,whereas others begin in the boreal summer and persist in a positive phase throughout the summer monsoon season.This study investigates the distinct influences of an exhausted spring El Nino(springtime)and emerging summer El Nino(summertime)on the regional variability of ISMR.The two ENSO categories were formulated based on the time of occurrence of positive SST anomalies over the Nino-3.4 region in the Pacific.The ISMR’s dynamical and thermodynamical responses to such events were investigated using standard metrics such as the Walker and Hadley circulations,vertically integrated moisture flux convergence(VIMFC),wind shear,and upper atmospheric circulation.The monsoon circulation features are remarkably different in response to the exhausted spring El Nino and emerging summer El Nino phases,which distinctly dictate regional rainfall variability.The dynamic and thermodynamic responses reveal that exhausted spring El Nino events favor excess monsoon rainfall over eastern peninsular India and deficit rainfall over the core monsoon regions of central India.In contrast,emerging summer El Nino events negatively impact the seasonal rainfall over the country,except for a few regions along the west coast and northeast India.