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Long-Term Trend in Potential Vorticity Intrusion Events over the Pacific Ocean： Role of Global Mean Temperature Rise

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Journal of Meteorological research 2017年第5期31卷 906-915页

作者： Debashis NATH Wen CHEN Xiaoqing LAN center for monsoon system research Institute of Atmospheric Physics Chinese Academy of Sciences

In this study, we examine a long-term increasing trend in subtropical potential vorticity （PV） intrusion events over the Pacific Ocean in relation to the global mean temperature rise, based on multiple reaualysis datasets. The fre- quency of the PV intrusions is closely related to the upper-tropospheric equatorial westerly duct and the subtropical jet （STJ）. An overall strengthening of the westerly duct and weakening of the STJ are found to be driven by the warming-induced strengthening of Walker circulation and regional changes in Hadley circulation on multi-dccadal timescalc, leading to an increase in the PV intrusion frequency over the tropics. The results are robust in all datasets. The multi-decadal strengthening in the Pacific Walker circulation is consistent with the global mean temperature rise. In this way, the PV intrusions are correlated with the wanning related global mean temperuate rise. When the interan- nual variability of ENSO is removed from the intrusion time series, the long-term trend in PV intrusions due to ex- ternal forcing associated with anthropogenic warming （global mean temperature rise） becomes clearer. The link between the global mean temperature rise and intrusion frequency is further verified by performing a correlation ana- lysis between the two. The significant （〉 95%） correlation coefficient is 0.85, 0.94, 0.84, 0.83, and 0.84 for ERA-40, ERA-Interim, NCEP-NCAR, JRA-55, and JRA-25, respectively. This unequivocally indicates that the global mean temperature rise can explain around 69%--88% of the variance related to the lung-term increase in PV intrusion fre- quency over the Pacific Ocean.

关键词： potential vorticity (PV) intrusion Pacific Ocean westerly duct subtropical jet Walker circulation glob-al warming

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Influence of monsoon over the Warm Pool on Interannual Variation on Tropical Cyclone Activity over the Western North Pacific

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Advances in Atmospheric Sciences 2008年第2期25卷 319-328页

作者：陈光华黄荣辉 center for monsoon system research Institute of Atmospheric Physics Chinese Academy of Sciences

The relationship between the interannual variation in tropical cyclone （TC） activity over the western North Pacific （WNP） and the thermal state over the warm pool （WP） is examined in this paper. The results show that the subsurface temperature in the WP is well correlated with TC geographical distribution and track type. Their relation is linked by the East Asian monsoon trough. During the warm years, the westward-retreating monsoon trough creates convergence and vorticity fields that are favorable for tropical cyclogenesis in the northwest of the WNP, whereas more TCs concentrating in the southeast result from eastward penetration of the monsoon trough during the cold years. The steering flows at 500 hPa lead to a westward displacement track in the warm years and recurving prevailing track in the cold years. The two types of distinct processes in the monsoon environment triggering tropical cyclogenesis are hypothesized by composites centered for TC genesis location corresponding to two kinds of thermal states of the WP. During the warm years, low-frequency intraseasonal oscillation is active in the west of the WNP such that eastward-propagating westerlies cluster TC genesis in that region. In contrast, during the cold years, the increased cyclogenesis in the southeast of the WNP is mainly associated with tropical depression type disturbances transiting from equatorially trapped mixed Rossby gravity waves. Both of the processes may be fundamental mechanisms for the inherent interannual variation in TC activity over the WNP.

关键词： monsoon warm pool interannual variation tropical cyclone

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Modulation of the Arctic Oscillation and the East Asian Winter Climate Relationships by the 11-year Solar Cycle

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Advances in Atmospheric Sciences 2012年第2期29卷 217-226页

作者：陈文周群 center for monsoon system research Institute of Atmospheric PhysicsChinese Academy of Sciences

The modulation of the relationship between the Arctic Oscillation （AO） and the East Asian winter climate by the 11-year solar cycle was investigated. During winters with high solar activity （HS）, robust warming appeared in northern Asia in a positive AO phase. This result corresponded to an enhanced anticyclonic flow at 850 hPa over northeastern Asia and a weakened East Asian trough （EAT） at 500 hPa. However, during winters with low solar activity （LS）, both the surface warming and the intensities of the anticyclonic flow and the EAT were much less in the presence of a positive AO phase. The possible atmospheric processes for this 11-year solar-cycle modulation may be attributed to the indirect influence that solar activity induces in the structural changes of AO. During HS winters, the sea level pressure oscillation associated with the AO became stronger, with the significant influence of AO extending to East Asia. In the meantime, the AO-related zonal-mean zonal winds tended to extend more into the stratosphere during HS winters, which implies a stronger coupling to the stratosphere. These trends may have led to an enhanced AO phase difference; thus the associated East Asian climate anomalies became larger and more significant. The situation tended to reverse during LS winters. Further analyses revealed that the relationship between the winter AO and surface-climate anomalies in the following spring is also modulated by the 11-year solar cycle, with significant signals appearing only during HS phases. Solar-cycle variation should be taken into consideration when the AO is used to predict winter and spring climate anomalies over East Asia.

关键词： AO East Asian winter climate solar activity East Asian trough

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Interannual Variability of the Winter Stratospheric Polar Vortex in the Northern Hemisphere and Their Relations to QBO and ENSO

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Advances in Atmospheric Sciences 2009年第5期26卷 855-863页

作者：陈文魏科 center for monsoon system research Institute of Atmospheric Physics Chinese Academy of Sciences

We investigated the interannual variations of the winter stratospheric polar vortex in this paper. EOF analysis shows that two modes of variability dominate the stratospheric polar vortex on interannual timescales The leading mode （EOF1） reflects the intensity variation of the polar vortex and is characterized by a geopotential height seesaw between the polar region and the mid-latitudes. The second one （EOF2） exhibits variation in the zonal asymmetric part of the polar vortex, which mainly describes the stationary planetary wave activity. As the strongest interannual variation signal in the atmosphere, the QBO has been shown to influence mainly the strength of the polar vortex. On the other hand, the ENSO cycle, as the strongest interannual variation signal in the ocean, has been shown to be mainly associated with the variation of stationary planetary wave activity in the stratosphere. Possible influences of the stratospheric polar vortex on the tropospheric circulation are also discussed in this paper.

关键词： stratospheric polar vortex EOF stationary wave QBO ENSO

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Determination of the Effect of Initial Inner-Core Structure on Tropical Cyclone Intensification and Track on a Beta Plane

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Advances in Atmospheric Sciences 2016年第8期33卷 945-954页

作者： Guanghua CHEN center for monsoon system research Institute of Atmospheric PhysicsChinese Academy of Sciences

The sensitivity of TC intensification and track to the initial inner-core structure on a β plane is investigated using a numerical model. The results show that the vortex with large inner-core winds（CVEX-EXP） experiences an earlier intensification than that with small inner-core winds（CCAVE-EXP）, but they have nearly the same intensification rate after spin-up. In the early stage, the convective cells associated with surface heat flux are mainly confined within the inner-core region in CVEXEXP, whereas the vortex in CCAVE-EXP exhibits a considerably asymmetric structure with most of the convective vortices being initiated to the northeast in the outer-core region due to the β effect. The large inner-core inertial stability in CVEX-EXP can prompt a high efficiency in the conversion from convective heating to kinetic energy. In addition, much stronger straining deformation and PBL imbalance in the inner-core region outside the primary eyewall ensue during the initial development stage in CVEX-EXP than in CCAVE-EXP, which is conducive to the rapid axisymmetrization and early intensification in CVEX-EXP. The TC track in CVEX-EXP sustains a northwestward displacement throughout the integration, whereas the TC in CCAVE-EXP undergoes a northeastward recurvature when the asymmetric structure is dominant. Due to the enhanced asymmetric convection to the northeast of the TC center in CCAVE-EXP, a pair of secondary gyres embedded within the large-scale primary β gyres forms, which modulates the ventilation flow and thus steers the TC to move northeastward.

关键词： inner-core structure tropical cyclone intensification track β plane

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Characteristics,Processes,and Causes of the Spatio-temporal Variabilities of the East Asian monsoon system

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Advances in Atmospheric Sciences 2012年第5期29卷 910-942页

作者：黄荣辉陈际龙王林林中达 center for monsoon system research Institute of Atmospheric PhysicsChinese Academy of Sciences

Recent advances in the study of the characteristics, processes, and causes of spatio-temporal variabilities of the East Asian monsoon （EAM） system are reviewed in this paper. The understanding of the EAM system has improved in many aspects： the basic characteristics of horizontal and vertical structures, the annual cycle of the East Asian summer monsoon （EASM） system and the East Asian winter monsoon （EAWM） system, the characteristics of the spatio-temporal variabilities of the EASM system and the EAWM system, and especially the multiple modes of the EAM system and their spatio-temporal variabilities. Some new results have also been achieved in understanding the atmosphere-ocean interaction and atmosphere-land interaction processes that affect the variability of the EAM system. Based on recent studies, the EAM system can be seen as more than a circulation system, it can be viewed as an atmosphere-ocean-land coupled system, namely, the EAM climate system. In addition, further progress has been made in diagnosing the internal physical mechanisms of EAM climate system variability, especially regarding the characteristics and properties of the East Asia-Pacific （EAP） teleconnection over East Asia and the North Pacific, the ＂Silk Road＂ teleconnection along the westerly jet stream in the upper troposphere over the Asian continent, and the dynamical effects of quasi-stationary planetary wave activity on EAM system variability. At the end of the paper, some scientific problems regarding understanding the EAM system variability are proposed for further study.

关键词： East Asian monsoon system spatio-temporal variations climate system EAP teleconnection

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Impact of Planetary Wave Reflection on Tropospheric Blocking over the Urals–Siberia Region in January 2008

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Advances in Atmospheric Sciences 2016年第3期33卷 309-318页

作者： Debashis NATH Wen CHEN center for monsoon system research Institute of Atmospheric Physics Chinese Academy of Sciences

Planetary wave reflection from the stratosphere played a significant role in changing the tropospheric circulation pattern over Eurasia in mid-January 2008. We studied the 2008 event and compared with composite analysis （winters of 2002/2003, 200412005, 200612007, 200712008, 201012011 and 2011/2012）, when the downward coupling was stronger, by employing time-lagged singular value decomposition analysis on the geopotential height field. In the Northern Hemisphere, the geopo- tential fields were decomposed into zonal mean and wave components to compare the relative covariance patterns. It was found that the wavenumber 1 （WN1） component was dominant compared with the wavenumber 2 （WN2） component and zonal mean process. For the WNI field, the covariance was much higher （lower） for the negative （positive） lag, with a prominent peak around ＋15 days when the leading stratosphere coupled strongly with the troposphere. It contributed to the downward coupling due to reflection, when the stratosphere exhibited a partially reflective background state. We also analyzed the evolution of the WNI anomaly and heat flux anomaly, both in the troposphere and stratosphere, during January- March 2008. The amplitude of the tropospheric WN 1 pattern reached a maximum and was consistent with a downward wave coupling event influenced by the stratospheric WN1 anomaly at 10 hPa. This was consistent with the reflection of the WN1 component over Eurasia, which triggered an anomalous blocking high in the Urals-Siberia region. We further clarified the impact of reflection on the tropospheric WNI field and hence the tropospheric circulation pattern by changing the propagation direction during and after the event.

关键词： planetary wave reflection singular value decomposition (SVD) Eliassen-Palm (EP) flux blocking circulation

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Recent Trends in Winter Temperature Extremes in Eastern China and their Relationship with the Arctic Oscillation and ENSO

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Advances in Atmospheric Sciences 2013年第6期30卷 1712-1724页

作者：陈尚锋陈文魏科 center for monsoon system research Institute of Atmospheric PhysicsChinese Academy of Sciences

Interannual variations in the number of winter extreme warm and cold days over eastern China （EC） and their relationship with the Arctic Oscillation （AO） and E1 Nifio-Southern Oscillation （ENSO） were investigated using an updated temperature dataset comprising 542 Chinese stations during the period 1961- 2011. Results showed that the number of winter extreme warm （cold） days across EC experienced a significant increase （decrease） around the mid-1980s, which could be attributed to interdecadal variation of the East Asian Winter monsoon （EAWM）. Probability distribution functions （PDFs） of winter temperature extremes in different phases of the AO and ENSO were estimated based on Generalized Extreme Value Distribution theory. Correlation analysis and the PDF technique consistently demonstrated that interannual variation of winter extreme cold days in the northern part of EC （NEC） is closely linked to the AO, while it is most strongly related to the ENSO in the southern part （SEC）. However, the number of winter extreme warm days across EC has little correlation with both AO and ENSO. Furthermore, results indicated that, whether before or after the mid-1980s shift, a significant connection existed between winter extreme cold days in NEC and the AO. However, a significant connection between winter extreme cold days in SEC and the ENSO was only found after the mid-1980s shift. These results highlight the different roles of the AO and ENSO in influencing winter temperature extremes in different parts of EC and in different periods, thus providing important clues for improving short-term climate prediction for winter temperature extremes.

关键词： AO ENSO East Asian Winter monsoon winter temperature extremes

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A Numerical Study on the Effect of an Extratropical Cyclone on the Evolution of a Midlatitude Front

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Advances in Atmospheric Sciences 2013年第5期30卷 1433-1448页

作者：陈光华 center for monsoon system research Institute of Atmospheric Physics Chinese Academy of Sciences

The extratropical transition （ET） of tropical cyclone （TC） Haima （2004） was simulated to understand the impact of TC on midlatitude frontal systems. Two experiments were conducted using the Advanced research version of the Weather research and Forecast （WRF） model. In the control run （CTL）, a vortex was extracted from the 24-hour pre-run output and then inserted into the National centers for Environmental Prediction （NCEP） global final （FNL） analysis as an initial condition, while TC circulation was removed from the initial conditions in the sensitivity run （NOTC）. Comparisons of the experiments demonstrate that the midlatitude front has a wider meridional extent in the NOTC run than that in the CTL run. Furthermore, the CTL run produces convection suppression to the southern side of the front due to strong cold advection related to the TC circulation. The easterly flow north of the TC not only decelerates the eastward displacement of the front and contracts its zonal scale but also transports more moisture westward and lifts the air along equivalent potential temperature surfaces ahead of the front. As a result, the ascending motion and diabatic heating are enhanced in the northeastern edge of the front, and the anticyclonic outflow in the upper-level is intensified. The increased pressure gradient and divergent ftow aloft strengthen the upper-level jet and distort the trough axis in a northwest-southeast orientation. The thermal contrast between the two systems and the dynamic contribution related to the TC circulation can facilitate scalar and rotational frontogenesis to modulate the frontal structure.

关键词： numerical study extratropical cyclone midlatitude front

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Investigating the Dominant Source for the Generation of Gravity Waves during Indian Summer monsoon Using Ground-based Measurements

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Advances in Atmospheric Sciences 2013年第1期30卷 153-166页

作者： Debashis NATH 陈文 center for monsoon system research Institute of Atmospheric PhysicsChinese Academy of Sciences

Over the tropics, convection, wind shear （i.e., vertical and horizontal shear of wind and/or geostrophic adjustment comprising spontaneous imbalance in jet streams） and topography are the major sources for the generation of gravity waves. During the summer monsoon season （June August） over the Indian subcontinent, convection and wind shear coexist. To determine the dominant source of gravity waves during monsoon season, an experiment was conducted using mesosphere-stratosphere-troposphere （MST） radar situated at Gadanki （13.5°N, 79.2°E）, a tropical observatory in the southern part of the Indian subcontinent. MST radar was operated continuously for 72 h to capture high-frequency gravity waves. During this time, a radiosonde was released every 6 h in addition to the regular launch （once daily to study low-frequency gravity waves） throughout the season. These two data sets were utilized effectively to characterize the jet stream and the associated gravity waves. Data available from collocated instruments along with satellite-based brightness temperature （TBB） data were utilized to characterize the convection in and around Gadanki. Despite the presence of two major sources of gravity wave generation （i.e., convection and wind shear） during the monsoon season, wind shear （both vertical shear and geostrophic adjustment） contributed the most to the generation of gravity waves on various scales.

关键词： convection wind shear gravity waves MST radar radiosonde

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