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1.
An analysis of the kinetic energy budget during a case of interaction between middle latitude and extratropical cyclones has been made in this work. Horizontal flux convergence constitutes a major energy sink. Generation of kinetic energy via cross-contour flow is a persistent source throughout the growth and decay periods. Dissipation of kinetic energy from subgrid to grid scales is an important source during the pre-storm period; it acts as a sink during the growth and decay periods. The major contribution to kinetic energy comes from a persistent upper tropospheric jet stream activity throughout the period of the cyclone development. The characteristics of moisture-flux components (divergent and rotational) along with precipitable water content for different tropospheric layers throughout the life cycle of our cyclone are also studied in this work. It is found that most of required humidity for our cyclone are initiated from Arabian Sea and then to some extent are reinforced over Gulf of Aden and east of central Africa and then by passing over Red sea enter to the south and south east of Mediterranean Sea. The rotational component of the moisture transport brings moisture from two regions; the first which is considered the main region is the Indian Ocean, Arabian Sea, Gulf of Aden and north east of Sudan. The second source region is the Atlantic and Mediterranean Sea. In the middle troposphere, the primary moisture source is found over central Africa, which in turn is traced to the Atlantic Ocean, the Indian Ocean, and the Arabian Sea. The upper-level moisture fluxes are weak and play a minor role over the area of interaction between two cyclones. 相似文献
2.
D. Subrahmanyam M. K. Tandon L. George S. K. Mishra 《Pure and Applied Geophysics》1981,119(5):901-912
The role of barotropic processes in the development of a monsoon depression, formed on 5 July 1979 during MONEX observational period, is studied by considering it as a quasi-geostrophic divergent barotropic instability problem of zonal flow of 3 July 1979 at 700 mb level. Numerical solutions are obtained by initial value approach. The preferred wave has a wavelength of 2750 km, an e-folding time of 4.3 days, a period of 6.5 days and an eastward phase speed of 4.9 ms–1. Structure of preferred wave is found to be in good agreement with the observed horizontal structure of the depression at 700 mb. Poleward momentum transports are found to predominate over equatorward transports.Parts of this paper were presented at the National Symposium on Early Results of MONEX-1979. 9–12 March 1981, in New Delhi, India. 相似文献
3.
The impact of Southern Oscillation on thecyclogenesis over the Bay of Bengal duringthe summer monsoon has been investigated.The analysis of correlation coefficients(CCs) between the frequency of monsoondepressions and the Southern OscillationIndex (SOI) reveals that more depressionsform during July and August of El Niñoyears. Due to this, the seasonal frequencyof monsoon depressions remains little higherduring El Niño epochs even though thecorrelations for June and September are notsignificant. The CCs for July and August aresignificant at the 99% level.The El Niño-Southern Oscillation (ENSO)is known to affect Indian MonsoonRainfall (IMR) adversely. The enhancedcyclogenesis over the Bay of Bengal duringJuly and August is an impact of ENSO whichneeds to be examined closely. Increasedcyclogenesis over the Bay of Bengal may bereducing the deficiency in IMR duringEl Niño years by producing more rainfallover the eastern parts of India duringJuly and August. Thus there is a considerablespatial variation in the impact of ENSOon the monsoon rainfall over India and El Niñoneed not necessarily imply a monsoonfailure everywhere in India.The area of formation of monsoon depressionsshifts eastward during El Niño years.Warmer sea surface temperature (SST) anomaliesprevail over northwest and adjoiningwestcentral Bay of Bengal during premonsoon andmonsoon seasons of El Niño years.May minus March SOI can provide useful predictionsof monsoon depression frequencyduring July and August. 相似文献
4.
The main advantages of constant potential enthalpy as a vertical coordinate are weaker horizontal velocity gradients in frontal
regions and a higher vertical resolution. A disadvantage is the intersection of isentropes with the ground and folding of
these surfaces. A numerical model is proposed to overcome the difficulties imposed by the intersection of isentropes with
the ground. The model contains a physical and computational domain. The top and bottom surfaces of the computational domain
are isentropes whereas the physical domain of the flow confined above by a free surface of constant pressure, and the bottom
of this domain is the surface of the earth. In the present study the top surfaces of these two domains coincide (θ
T, PTare constants in space and time). The model was tested for the study of frontogenesis and cyclogenesis and integrated for
7 days. The results correspond to enstrophy-conserving finite difference scheme. 相似文献
5.
The French Transportable Laser Ranging System (FTLRS) was deployed in the calibration site of satellite radar altimeters in Corsica over the 2002 and 2005 campaigns. The paper describes the different steps of SLR data processing. The average arcs RMS obtained are about 1–2 cm for Lageos-1&;-2, Starlette and Stella satellites; it is shown that the best results of satellite orbits determination and geocentric positioning are obtained with Eigen-Grace03s gravity model. The difference of FTLRS absolute 3D positioning, between 2002 and 2005, of about 7.7 mm (i.e., 2.6 mm/yr) is less than residual errors of ITRF2005 velocities (of about 4.3 mm/yr). 相似文献
6.
This paper discusses the synoptic factors contributing to the formation of thunderstorms in western Europe and in particular gives reasons for the existence of the preferred areas for thunderstorms. These areas are all found in the vicinity of the Alps. The synoptic features playing a role in promoting thunderstorm formation in particular areas in western Europe are identified. The principle synoptic features or processes promoting the formation of intense thunderstorms are a high level of potential instability, convergence lines associated with frontogenesis and cyclogenesis and upper level potential vorticity advection. Additional features playing a role in thunderstorm formation are land and seabreeze circulations and (thermally) forced upward motion at slopes. 相似文献
7.
8.
Canonical balanced dynamic equations involving vertically sheared horizontal flow with heat or mass sources have emerged recently in systematic multi-scale modeling of the equatorial wave guide on a wide range of spatio-temporal scales. Here, a new self-contained derivation of these equations is developed briefly in a context for potential applications to the hurricane embryo. These canonical balanced equations are studied through a combination of exact solutions and simple numerics. The results below include elementary exact solutions given by velocity fields that are linear in the spatial coordinates combined with an exact nonlinear stability analysis for vertical vorticity amplification in such a preconditioned environment. Other elementary solutions studied here include the evolution of radial eddies, which represent “hot towers” in the hurricane embryo in a suitable radial preconditioned background environment. 相似文献
9.
The lateral motion of the Gulf Stream off the eastern seaboard of the United States during the winter season can act to dramatically enhance the low-level baroclinicity within the coastal zone during periods of offshore cold advection. The ralative close proximity of the Gulf Stream current off the mid-Atlantic coast can result in the rapid and intense destabilization of the marine atmospheric boundary layer directly above and shoreward of the Gulf Stream within this region. This airmass modification period often precedes either wintertime coastal cyclogenesis or the cyclonic re-development of existing mid-latitude cyclones. A climatological study investigating the relationship between the severity of the pre-storm, cold advection period and subsequent cyclogenic intensification was undertaken by Cione et al. in 1993. Findings from this study illustrate that the thermal structure of the continental airmass as well as the position of the Gulf Stream front relative to land during the pre-storm period (i.e., 24–48 h prior to the initial cyclonic intensification) are linked to the observed rate of surface cyclonic deepening for storms that either advected into or initially developed within the Carolina-southeast Virginia offshore coastal zone. It is a major objective of this research to test the potential operational utility of this pre-storm low level baroclinic linkage to subsequent cyclogenesis in an actual National Weather Service (NWS) coastal winter storm forecast setting.The ability to produce coastal surface cyclone intensity forecasts recently became available to North Carolina State University researchers and NWS forecasters. This statistical forecast guidance utilizes regression relationships derived from a nine-season (January 1982–April 1990), 116-storm study conducted previously. During the period between February 1994 and February 1996, the Atlantic Surface Cyclone Intensification Index (ASCII) was successfully implemented in an operational setting by the NWS at the Raleigh-Durham (RAH) forecast office for 10 winter storms. Analysis of these ASCII forecasts will be presented. 相似文献
10.
气旋生成机制的位涡反演诊断 总被引：10，自引：2，他引：8
本文采用位涡反演方法,对一次西太平洋地区爆发性气旋的生成机制进行了诊断分析。结果表明：高层位涡扰动（即高空槽脊系统）所诱生的低层扰动风场特征为一支位于高空槽前下方的偏南气流,这支偏南气流是促使低层锋区扰动发展的主要动力因子：而低层位涡扰动（即低层锋区扰动）所诱生的低层扰动位势场和扰动风场是低层降压和气旋性环流生成的主要原因。 相似文献