Some structural characteristics of pre-monsoon depression in the Bay of Bengal

During the period 6 to 16 May. 1995. three deep depressions formed one after another over west Bay of Bengal and moved from south to north. In this paper, structural characteristics of these systems are investigated from the distribution of thermal and thermodynamical field observed around the depression center utilising daily Rs/Rw and other available coastal observations during the period, Major findings of the study are: (i) The depressions have low level cold core and middle and upper tropospheric warm core. (ii) Thermal and moisture fields tilt north ward with height but vertical tilt of contour height is .not uniform at all levels, (iii) During intensification of the system significant increase in temperature and moisutre occurs above 700 hPa and significant fall of contour height occurs below 300 hPa.

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Development of a Monsoon Depression and Its Interaction with the Large-Scale Background: A Case Study

Monthly Weather Review ◽

10.1175/mwr-d-21-0084.1 ◽

2021 ◽

Vol 149 (11) ◽

pp. 3627-3646

Author(s):

S. K. Mishra

Keyword(s):

Large Scale ◽

Baroclinic Instability ◽

Lower Troposphere ◽

Monsoon Depression ◽

Necessary Condition ◽

Synoptic Scale ◽

Warm Core ◽

Barotropic Energy Conversion ◽

Cold Core

Abstract Structure and time evolution of the large-scale background and an embedded synoptic-scale monsoon depression and their interactions are studied. The depression formation is preceded by a cyclonic circulation around 400 hPa. The Fourier-based scale separation technique is used to isolate large (wavenumbers 0–8) and synoptic-scale (wavenumbers 12–60). The wavelength and depression center is determined objectively. The synoptic-scale depression has an average longitudinal wavelength of around 1900 km and a north–south size of 1100 km; it is most intense with a vorticity of 20.5 × 10 −5 s −1 at 900 hPa. The strongest cold core of −3.0°C below 850 hPa and the above warm core of around 2.0°C are evident. The depression is tilted southwestward in the midtroposphere with no significant vertical tilt in the lower troposphere. The mean maximum intensity and upward motion over the life cycle of depression are in close agreement with the composite values. A strong cyclonic shear zone is developed in the midtroposphere preceding the depression. The necessary condition for barotropic (baroclinic) instability is satisfied in the midtroposphere (boundary layer). Strong northward transport of momentum by the depression against the southward shear is found. The strong growth of the MD in the lower troposphere is due to downward transfer of excess energy gained in the midtroposphere from the barotropic energy conversion and east–west direct thermal circulation as the vertical energy flux. The baroclinic interaction contributes to the maintenance of the cold core in the lower troposphere. The diabatic heating rate is computed and its role in the genesis and growth of MD is investigated.

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Tornadoes with Cold Core 500-mb Lows

Weather and Forecasting ◽

10.1175/waf967.1 ◽

2006 ◽

Vol 21 (6) ◽

pp. 1051-1062 ◽

Cited By ~ 7

Author(s):

Jonathan M. Davies

Keyword(s):

United States ◽

Severe Weather ◽

Surface Heating ◽

Vertical Shear ◽

Cold Temperatures ◽

Low Level ◽

Close Proximity ◽

Central United States ◽

Surface Patterns ◽

Cold Core

Abstract Tornadoes that occur in close proximity to midlevel closed lows with a core of cold temperatures aloft are not uncommon, particularly in the central United States. Although several informal studies have shown that severe weather and tornadoes can occur with these midlevel lows, little in the way of formal work has been published documenting features and ingredients of such systems, especially those that produce what are sometimes called cold core tornadoes. Of particular concern is that these tornadoes can be associated with surface and low-level moisture that appears deceptively small or marginal regarding severe weather potential, yet on occasion tornadoes of F2 or greater intensity can develop. In other cases, vertical shear may appear relatively weak at locations close to the midlevel low, suggesting little potential for tornadoes. These “atypical” characteristics can result in poor anticipation by forecasters of tornado events associated with closed 500-mb lows. This note documents some synoptic and mesoscale features commonly associated with tornado events in close proximity to cold core 500-mb lows using four tornadic cases in Kansas as examples, including photographs to show the small nature of storms associated with such systems. Recognition of surface patterns with a particular organization of boundaries and surface heating positioned near midlevel lows, along with the presence of some amount of buoyancy, can help with the operational awareness of the potential for tornadoes in many 500-mb closed low settings.

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Statistical Characteristics of Cyclonic Warm-Core Eddies and Anticyclonic Cold-Core Eddies in the North Pacific Based on Remote Sensing Data

Remote Sensing ◽

10.3390/rs11020208 ◽

2019 ◽

Vol 11 (2) ◽

pp. 208 ◽

Cited By ~ 10

Author(s):

Wenjin Sun ◽

Changming Dong ◽

Wei Tan ◽

Yijun He

Keyword(s):

Remote Sensing ◽

North Pacific ◽

Kuroshio Extension ◽

Remote Sensing Data ◽

Statistical Characteristics ◽

The North ◽

Warm Core ◽

Spatio Temporal ◽

Cold Core ◽

The North Pacific

A (an) cyclonic (anticyclonic) eddy is usually associated with a cold (warm) core caused by the eddy-induced divergence (convergence) motion. However, there are also some cyclonic (anticyclonic) eddies with warm (cold) cores in the North Pacific, named cyclonic warm-core eddies (CWEs) and anticyclonic cold-core eddies (ACEs) in this study, respectively. Their spatio-temporal characteristics and regional dependence are analyzed using the multi-satellite merged remote sensing datasets. The CWEs are mainly concentrated in the northwestern and southeastern North Pacific. However, besides these two areas, the ACEs are also concentrated in the northeastern Pacific. The annual mean number decreases year by year for both CWEs and ACEs, and the decreasing rate of the CWEs is about two times as large as that of the ACEs. Moreover, the CWEs and ACEs also exhibit a significant seasonal variation, which are intense in summer and weak in winter. Based on the statistics of dynamic characteristics in seven subregions, the Kuroshio Extension region could be considered as the most active area for the CWEs and ACEs. Two possible mechanisms for CW-ACEs generation are discussed by analyzing two cases.

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The comparison of warm-core and cold-core designs of iron-cored HTS inductors for electric power applications

Physica C Superconductivity ◽

10.1016/j.physc.2008.05.202 ◽

2008 ◽

Vol 468 (15-20) ◽

pp. 2149-2151

Author(s):

C. Chao ◽

C. Grantham

Keyword(s):

Electric Power ◽

Warm Core ◽

Cold Core

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Tropical Transition of an Unnamed, High-Latitude, Tropical Cyclone over the Eastern North Pacific

Monthly Weather Review ◽

10.1175/mwr-d-15-0213.1 ◽

2016 ◽

Vol 144 (2) ◽

pp. 713-736 ◽

Cited By ~ 8

Author(s):

Alicia M. Bentley ◽

Nicholas D. Metz

Keyword(s):

Life Cycle ◽

Tropical Cyclone ◽

Cross Sections ◽

North Pacific ◽

Lower Troposphere ◽

Sea Surface ◽

The West ◽

Warm Core ◽

Cold Core ◽

North Pacific Basin

Abstract In early November 2006, an unnamed tropical cyclone (TC) formed via the tropical transition (TT) process at 42°N over the eastern North Pacific. An extratropical cyclone (EC), developing downstream of a thinning upper-tropospheric trough over the eastern North Pacific, served as the precursor disturbance that would ultimately undergo TT. The TT of the unnamed TC was extremely unusual—occurring over ~16°C sea surface temperatures in a portion of the eastern North Pacific basin historically devoid of TC activity. This paper 1) identifies the upper- and lower-tropospheric features linked to the formation of the EC that transitions into the unnamed TC, 2) provides a synoptic overview of the features and processes associated with the unnamed TC’s TT, and 3) discusses the landfall of the weakening cyclone along the west coast of North America. As observed in previous studies of TT, the precursor EC progresses through the life cycle of a marine extratropical frontal cyclone, developing a bent-back warm front on its northern and western sides and undergoing a warm seclusion process. Backward air parcel trajectories suggest that air parcels isolated in the center of the transitioning cyclone were warmed in the lower troposphere via sensible heating from the underlying sea surface. Vertical cross sections taken through the center of the cyclone during its life cycle reveal its transformation from an asymmetric, cold-core, EC into an axisymmetric, warm-core, TC during TT. Ensemble reforecasts initialized after TT highlight the relatively low forecast skill associated with the landfall of the weakening cyclone.

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Local Oceanic Precursors for the Summer Monsoon Onset over the Bay of Bengal and the Underlying Processes

Journal of Climate ◽

10.1175/jcli-d-15-0825.1 ◽

2016 ◽

Vol 29 (23) ◽

pp. 8455-8470 ◽

Cited By ~ 5

Author(s):

Nan Xing ◽

Jianping Li ◽

Xingwen Jiang ◽

Lanning Wang

Keyword(s):

Summer Monsoon ◽

Gravity Waves ◽

Bay Of Bengal ◽

Surface Heat ◽

Sea Surface ◽

Subtropical High ◽

Interannual Time Scale ◽

Low Level ◽

Summer Monsoon Onset ◽

Underlying Processes

Abstract Local sea surface temperature (SST) plays an important role in the onset of the Bay of Bengal (BoB) summer monsoon (BoBSM). Previous study indicated that the meridionally warmest SST axis (WSSTA) appears in mid-April in the central BoB, which may be a precursor for the BoBSM onset. In this study, it is found that a warm but not the meridionally warmest center, which is defined as the secondary WSSTA (SWSSTA), occurs in early April in the central BoB, leading the BoBSM onset by five pentads. Dates of the SWSSTA occurrence are significantly positively correlated with dates of the WSSTA occurrence in the central BoB and the BoBSM onset on an interannual time scale. The SWSSTA is an earlier precursor for the BoBSM onset. The formation of the oceanic precursor and its impact on the BoBSM onset are as follows. Before the BoBSM onset, resulting from more surface heat input and shallower mixed layer affected by the low-level anticyclone and subtropical high in the central BoB, local SST shows the most rapid increase. Meanwhile, the situation is adverse to the rapid increase of SST in the equatorial BoB. For this reason, the SWSSTA occurs, and the WSSTA subsequently appears in the central BoB. The WSSTA in turn enhances local convection, eliminates the low-level anticyclone, and moves the subtropical high outward away from the BoB by inducing atmospheric instability, thus developing a heating center. Convectional heating further strengthens southwesterlies in the BoB by exciting mixed planetary–gravity waves, resulting in the BoBSM onset.

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Moisture and Energy Budget Perspectives on Summer Drought in North China

Journal of Climate ◽

10.1175/jcli-d-20-0176.1 ◽

2020 ◽

Vol 33 (23) ◽

pp. 10149-10167

Author(s):

Lan Dai ◽

Jonathon S. Wright ◽

Rong Fu

Keyword(s):

Energy Budget ◽

Large Scale ◽

North China ◽

Static Stability ◽

Summer Drought ◽

Warm Core ◽

Budget Analysis ◽

Moisture Advection ◽

Upper Level ◽

Cold Core

AbstractWe investigate the physical processes behind summer drought in North China by evaluating moisture and energy budget diagnostics and linking them to anomalous large-scale circulation patterns. Moisture budget analysis reveals that summer drought in North China was caused dynamically by reduced vertical moisture advection due to anomalous subsidence and reduced horizontal moisture advection due to anomalous northeasterly winds. Energy budget analysis shows that reduced latent heating was balanced dynamically by decreased dry static energy (DSE) divergence in the middle-to-upper troposphere. Linking these results to previous work, we suggest that summer drought in North China was predicated on co-occurrence of the positive phases of the Eurasian (EU) and Pacific–Japan (PJ) teleconnection patterns, potentially modulated by the circumglobal teleconnection (CGT). In the typical case, the negative phase of the CGT intensified the positive EU-related upper-level cyclone. Resulting upper-level cooling and positive surface feedback imposed a cold-core surface anticyclone that weakened with height. By contrast, when the positive phase of the CGT occurred in tandem with the positive EU and PJ patterns, the anticyclone had a warm core and intensified with height. The two cases were unified by strong subsidence but exhibited opposite meridional advection anomalies. In the cold-core cases, meridional moisture inflow was reduced but meridional DSE export was enhanced, further limiting precipitation while maintaining negative thermal anomalies. In the warm-core case, which only occurred once, enhanced meridional inflow of water vapor supplied moisture for sporadic precipitation while reduced meridional DSE export helped to maintain strong static stability.

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Mesoscale Convection and Bimodal Cyclogenesis over the Bay of Bengal

Monthly Weather Review ◽

10.1175/mwr-d-14-00260.1 ◽

2015 ◽

Vol 143 (9) ◽

pp. 3495-3517 ◽

Cited By ~ 4

Author(s):

Nasreen Akter

Keyword(s):

Bay Of Bengal ◽

Deep Convection ◽

Leading Edge ◽

Vertical Shear ◽

Squall Line ◽

Convergence Zone ◽

Low Level ◽

Convective Systems ◽

Mesoscale Convective ◽

Long Time

Abstract Mesoscale convective systems (MCSs) are an essential component of cyclogenesis, and their structure and characteristics determine the intensity and severity of associated cyclones. Case studies were performed by simulating tropical cyclones that formed during the pre- and postmonsoon periods in 2007 and 2010 over the Bay of Bengal (BoB). The pre- (post) monsoon environment was characterized by the coupling of northwesterly (southwesterly) wind to the early advance southwesterly (northeasterly) monsoonal wind in the BoB. The surges of low-level warm southwesterlies with clockwise-rotating vertical shear in the premonsoon period and moderately cool northeasterlies with anticlockwise-rotating vertical shear in the postmonsoon period transported moisture and triggered MCSs within preexisting disturbances near the monsoon trough over the BoB. Mature MCSs associated with bimodal cyclone formations were quasi linear, and they featured leading-edge deep convection and a trailing stratiform precipitation region, which was very narrow in the postmonsoon cases. In the premonsoon cases, the MCSs became severe bow echoes when intense and moist southwesterlies were imposed along the dryline convergence zone in the northern and northwestern BoB. However, the development formed a nonsevere and nonorganized linear system when the convergence zone was farther south of the dryline. In the postmonsoon cases, cyclogenesis was favored by squall-line MCSs with a north–south orientation over the BoB. All convective systems moved quickly, persisted for a long time, and contained suitable environments for developing low-level cyclonic mesovortices at their leading edges, which played an additional role in forming mesoscale convective vortices during cyclogenesis in the BoB.

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Simulation of Synoptic- and Subsynoptic-Scale Phenomena Associated with the East Asian Summer Monsoon Using a High-Resolution GCM

Monthly Weather Review ◽

10.1175/2008mwr2511.1 ◽

2009 ◽

Vol 137 (1) ◽

pp. 137-160 ◽

Cited By ~ 42

Author(s):

Ngar-Cheung Lau ◽

Jeffrey J. Ploshay

Keyword(s):

Summer Monsoon ◽

Bay Of Bengal ◽

General Circulation ◽

Asian Monsoon ◽

Asian Summer Monsoon ◽

East Asian ◽

Western Pacific ◽

Low Level ◽

Continental Scale ◽

Asian Summer

Abstract A 20-yr simulation using a global atmospheric general circulation model with a resolution of 0.5° latitude × 0.625° longitude is compared with observational findings. The primary goal of this survey is to assess the model performance in reproducing various summertime phenomena related to the continental-scale Asian monsoon in general, and the regional-scale East Asian monsoon in particular. In both model and observed atmospheres, the seasonal march of the precipitation centers associated with the Asian summer monsoon is characterized by onsets occurring earliest over the southeastern Bay of Bengal, followed by rapid northeastward advances over Indochina, the South China Sea–Philippine Sea and the western Pacific, northward evolution in the East Asian sector, as well as northwestward development over the Bay of Bengal, the Indian subcontinent, and the Arabian Sea. This onset sequence is accompanied by southwesterly low-level flows over the rainy regions, as well as northwestward migration of the 200-mb Tibetan anticyclone. Analysis of the heat sources and sinks in various regions illustrates the prominent role of condensational heating in the local energy budget during the mature phases of monsoon development. In accord with observations, the simulated monsoon rains in the East Asian sector are organized about zonally elongated “mei-yu–baiu” (plum rain) systems. These precipitation features advance to higher latitudes during the June–July period, in conjunction with displacements of the axis of the low-level anticyclone over the subtropical western Pacific. A detailed case study is performed on a prominent rainy episode in the simulation. The model is capable of reproducing the observed intense gradients in temperature, humidity, and moist static stability in the vicinity of the mei-yu–baiu front, as well as the spatial relationships between the rainband and the three-dimensional flow field. The axis of the mei-yu–baiu rainband in this event is aligned with the trajectory of a succession of mesoscale cyclonic vortices, which originate from southwestern China and travel northeastward over the Yangtze River basin.

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