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1.
V. Krishnakumar R. N. Keshavamurty S. V. Kasture 《Journal of Earth System Science》1992,101(2):123-152
The objective of this study was two-fold: the first to investigate the role of moist convection and nongeostrophic effects
on the growth of the monsoon depressions using a linearized multi-level moist primitive equation (PE) model and quasi-geostrophic
(QG) model with only vertical shear. The second was to study the nonlinear evolution, growth, movement and detailed energetics
of the monsoon depressions using a nonlinear moist global spectral model.
Our linear studies using both models revealed lower as well as upper tropospheric growing modes. For the lower tropospheric
modes the shorter scales were found to grow faster. While the PE model showed faster growth rate for shorter scales, as compared
to longer scales, the QG model showed less tendency for scale selection. The shorter scales in PE model had phase speeds ranging
from 4 to — 1 ms−1 and in QG model from 8 to — 4 ms−1. The nongeostrophic effects were found to be, in general, important.
One of the lower tropospheric modes with wavelength 2500 km was found to have many features similar to the observed monsoon
depression of the Bay of Bengal.
In the upper troposphere the PE model showed much faster growth rates compared to the QG model. Also the fastest growing mode
with a doubling time of 2.5 days had a scale of 6000 km. This was shorter than the scale predicted in the QG model. This mode
had many characteristics similar to the observed features of the monsoon upper tropospheric easterly waves.
Using a nonlinear global spectral model, we simulated the monsoon depression around 21°N starting from an antisymmetric heating
distribution (with respect to the equator) and with a specific vertical structure with and without basic flows. The model
was integrated for a period of five days incorporating a simple form of cumulus heating. The simulated model disturbance showed
a pronounced growth and a westward movement in the presence of cumulus heating. The detailed energetics calculations revealed
that the baroclinic energy exchange is the primary energy exchange process and cumulus heating is the driving force for the
generation of available potential energy. 相似文献
2.
A K SRIVASTAVA SOMENATH DUTTA S R KSHIRSAGAR KAVITA SRIVASTAVA 《Journal of Earth System Science》2014,123(3):445-456
In the paper, influence of extratropical circulation features on Indian Summer Monsoon Rainfall (ISMR) is examined. Energetics of extratropics, north of Indian subcontinent for deficient and non-deficient ISMR years, during two periods 1951–1978 and 1979–2005, are calculated and critically analyzed. It is observed that for the period 1951–1978, only two out of the 10 energetics parameters, viz., the zonal available potential energy (high) and conversion of zonal kinetic energy to eddy kinetic energy (low) differed significantly in JJA months of the deficient years from that of the non-deficient years. However, during the 1979–2005 period, as many as six out of the 10 energetics parameters, viz., eddy available potential energy, zonal available potential energy, eddy kinetic energy, generation of zonal available potential energy, conversion of zonal available potential energy to zonal kinetic energy and conversion of zonal kinetic energy to eddy kinetic energy differed significantly in JJA months of the deficient years from that of the non-deficient years. These results confirm growing influence of the transient stationary waves in deficient years after the climate shift year, 1979. Analysis of energetics parameters of the pre-monsoon season of the two periods also reveals similar results. This suggests that forcings apparently responsible for energetics in JJA months of the deficient years of the later period were present even before the advent of Indian summer monsoon season. 相似文献
3.
Vertical distributions of various components of the tropospheric global rotational kinetic energy, enstrophy and available
potential energy during July 1979, and the contributions to these from different zonal wave categories were studied. Representative
levels in the lower and upper troposphere for the stationary and transient energetics were identified on the basis of different
components of energy and enstrophy. The eddy energy and enstrophy contained in different zonal scale components in the lower
and upper troposphere were studied to find out the preferred scales for stationary and transient monsoonal motion in the two
atmospheric layers. The role of different zonal wave categories in the nonlinear exchanges of energy and enstrophy arising
due to stationary-stationary, transient-transient, stationary-transient and observed flow interactions was examined. Stationary
and transient global spectra of the aforesaid dynamical variables in terms of the zonal wavenumber(m) with triangular truncation
atm = 42 were utilized for this purpose.
It was found from the global average kinetic energy in lower and upper troposphere that the global stationary and transient
motions were comparable in the lower troposphere while in the upper troposphere stationary motion dominated over the transient
motion. The computed zonal and eddy energy confirmed that the stationary motion was predominantly zonal while the transient
motion was dominated by eddies. From the time mean nonlinear interaction of kinetic energy (enstrophy) of observed flow it
was seen that the long and short waves as well as the zonal flow gained kinetic energy (enstrophy) from medium waves due to
nonlinear interactions. The transfer of available potential energy due to nonlinear interaction was down the scale except
for short waves in the upper troposphere. The stationary-transient interaction was found to be an important element of the
spatial-temporal varying atmospheric flow. 相似文献
4.
L S Hingane 《Journal of Earth System Science》1984,93(2):105-110
Global analyses of zonal wind field and thermal field structure at standard pressure levels of 200,150 and 100 mb have been carried out in India during July 1979—a poor monsoon year and July 1975—a good monsoon year. More than 250 stations in the belt 60°N and 60°S were selected. Contrasting features of the zonal wind field structure and thermal field are brought out, and it is shown that monsoon activity is reflected in the upper level and is controlled by planetary scale. 相似文献
5.
A detailed barotropic, baroclinic and combined barotropic-baroclinic stability analysis has been carried out with mean monsoon
zonal currents over western India, eastern India and S.E. Asia. The lower and middle tropospheric zonal wind profiles over
western India are barotropically unstable. The structure and growth rate of these modes agree well with the observed features
of the midtropospheric cyclones. Similar profiles over eastern India and S.E. Asia, however, are barotropically stable. This
is attributed to weak horizontal shear, inherent to these profiles. The upper tropospheric profiles, on the other hand, are
barotropically unstable throughout the whole region. The features of these unstable modes agree with those of observed easterly
waves. The baroclinic and combined barotropic-baroclinic stability analyses show that the baroclinic effects are not important
in tropics.
Though the barotropic instability of the mean zonal current seems to be res ponsible for the initial growth of the mid-tropospheric
cyclones, neither barotropic nor baroclinic instability of the mean zonal current seem to explain the observed features of
the monsoon depressions. 相似文献
6.
Global analyses of mean monthly zonal wind component and temperature at 200, 150 and 100 mb levels have been made for the
region between 60°N and 60°S, for the months May through September during two poor monsoon years (1972 and 1979) and a good
monsoon year (1975). Prominent and consistent contrasting features of the zonal wind and thermal fields have been identified,
with reference to the monsoon performance over India. It has been noticed that the areal spreading of easterlies over the
tropics and extratropics is significantly more during a good monsoon year. Shifting of the axis of the tropical easterly jet
stream to a higher level and generally stronger easterlies also characterize good monsoon activity. The upper troposphere
has been found to be considerably cooler during poor monsoon years. 相似文献
7.
Barotropic stability of a stationary Rossby wave of wavelength 30° longitude superposed on the uniform monsoon zonal flow has been examined. The wave is unstable to perturbations and the growth rate depends on the meridional scale. These perturbations grow by drawing on the kinetic energy of the stationary Rossby wave. 相似文献
8.
S. M. Bawiskar M. D. Chipade D. K. Paul S. S. Singh 《Journal of Earth System Science》1995,104(4):613-634
Kinetic energy exchange equations (Saltzman 1957) in wave number domain are partitioned into standing, transient and standing-transient
components following Murakami (1978, 1981). These components are computed for the 1991 summer monsoon using dailyu andv grid point data at 2.5° latitude-longitude interval between the equator and 40°N at 200 hPa and 850 hPa levels for the period
June through August. The data are obtained from NCMRWF, New Delhi.
The study shows that at 200 hPa wave number 1 over Region 3 (30°N to 40°N), wave number 2 over Region 2 (15°N to 30°N) and
wave number 3 over Region 1 (equator to 15°N) dominate the spectrum of transport of momentum and wave to zonal mean flow interaction.
Wave number 1 over Region 1 and Region 3 and wave number 2 over Region 2 are the major sources of kinetic energy to other
waves via wave-to-wave interaction. At 850 hPa wave number 1 over Region 3 has maximum contribution in the spectrum of transport
of momentum and kinetic energy and more than 90% of its contribution is from the standing component. This indicates that standing
wave number 1 over Region 3 plays a very important role in the dynamics of monsoon circulation of the lower troposphere.
The study further shows that although the circulation patterns at 200 hPa and 850 hPa levels are opposite in character, a
number of energy processes exhibit a similar character at these levels. For example, (i) transport of momentum by most of
the waves is northward, (ii) small scale eddies intensify northward, (iii) eddies are sources of kinetic energy to zonal mean
flow over Region 1 and (iv) standing eddies are sources of kinetic energy to transient eddies. Besides the above similarities
some contrasting energy processes are also observed. Over Region 2 and Region 3 standing and transient eddies are sources
of kinetic energy to zonal mean flow at 200 hPa, while at 850 hPa the direction of exchange of kinetic energy is opposite
i.e. zonal mean flow is a source of kinetic energy to standing as well as transient eddies. L(n) interaction indicates that at 200 hPa waves over R2 maintain waves over R1, while at 850 hPa waves over R1 maintain waves
over R2.
It has been found that the north-south gradient of zonal mean of zonal wind is the deciding factor of wave to zonal mean flow
interaction. 相似文献
9.
The characteristic features of the marine boundary layer (MBL) over the Bay of Bengal during the southwest monsoon and the
factors influencing it are investigated. The Bay of Bengal and Monsoon Experiment (BOBMEX) carried out during July–August
1999 is the first observational experiment under the Indian Climate Research Programme (ICRP). A very high-resolution data
in the vertical was obtained during this experiment, which was used to study the MBL characteristics off the east coast of
India in the north and south Bay of Bengal. Spells of active and suppressed convection over the Bay were observed, of which,
three representative convective episodes were considered for the study. For this purpose a one-dimensional multi-level PBL
model with a TKE-ε closure scheme was used. The soundings, viz., the vertical profiles of temperature, humidity, zonal and
meridional component of wind, obtained onboard ORV Sagar Kanya and from coastal stations along the east coast are used for
the study. The temporal evolution of turbulent kinetic energy, marine boundary layer height (MBLH), sensible and latent heat
fluxes and drag coefficient of momentum are simulated for different epochs of monsoon and monsoon depressions during BOBMEX-99.The
model also generates the vertical profiles of potential temperature, specific humidity, zonal and meridional wind. These simulated
values compared reasonably well with the observations available from BOBMEX. 相似文献
10.
S. K. Roy Bhowmik 《Journal of Earth System Science》2003,112(4):499-519
At the India Meteorological Department (IMD), New Delhi, a 12-level limited area model with 100 km horizontal resolution has
been in use for weather forecasting. The present study uses this model together with a higher horizontal resolution (50 km)
and vertical resolution (16-levels) model to examine the impact of increased resolution to simulate mesoscale features of
rainfall during monsoon disturbances. The model was run for 22 days in the month of August 1997 and one week in September
1997 during three monsoon depressions and one cyclonic storm in the Bay of Bengal. The model results are compared with observations.
The study shows that the model can capture mesoscale convective organization associated with monsoon depression. 相似文献
11.
Kilometre-scale cylindrical folds and associated parasitic folds that trend at small angles to the transport lineation are analysed along a 100-km-long transport-normal segment of the Cycladic Blueschists in an attempt to reconstruct the 3D structural architecture within an exhumation channel. Reversals in the polarity of both fold vergence and the hinge/lineation obliquity occur in a flow-normal direction, defining transport-parallel culmination and depression surfaces that root downwards onto an underlying detachment. Fold patterns generated around culmination and depression surfaces support models of flow-perturbation folding where folds initiate at small angles or sub-parallel to transport in response to wrench-dominated differential shearing. Successive culmination and depression surfaces are separated from one another by along strike distances of ∼20 km, although atypical fold geometries developed in the flanks of major culmination and depressions follow their own patterns, revealing that smaller perturbations occur within the larger scheme. Major culminations are interpreted to reflect regions of surging flow marked by increased velocity during exhumation, whilst the opposite is true for depressions. This behaviour implies that on a regional scale, differential shear varies laterally in an irregular-sinusoidal manner defining areas of relative high and relative low displacement within the exhumation channel. 相似文献
12.
为深化洼地空间分布及其影响因素的认识,以云南石林县为例,在ArcGIS中基于DEM提取洼地分布及相关数据,并运用K函数（Ripley’s K）、核密度函数、缓冲区、空间叠加等分析方法,探讨了该区洼地密度分布特征及地理环境对其的影响。结果表明:研究区洼地在8 km尺度上为聚集分布模式,可划分为高密度（＞6个?km-2）、中密度（5～6个?km-2）和低密度（＜5个?km-2）三个区域。受多种地理环境因素影响,研究区洼地密度在不同海拔段、坡度、起伏度、地层岩石和断层缓冲区上均有差异性表现;同时,岩层节理、断层方向在一定程度上控制了洼地长轴的发育。研究区潜在水文连通性、面积—高程积分值两个指标与洼地密度呈现良好的一致性,但两个指标所反映的喀斯特洼地的地貌学意义还需进一步研究。 相似文献
13.
U. C. Mohanty N. V. Sam S. Das A. N. V. Satyanarayana 《Journal of Earth System Science》2003,112(2):147-163
Convective activity is one of the major processes in the atmosphere influencing the local and large-scale weather in the tropics.
The latent heat released by the cumulus cloud is known to drive monsoon circulation, which on the other hand supplies the
moisture that maintains the cumulus clouds. An investigation is carried out on the convective structure of the atmosphere
during active and suppressed periods of convection using data sets obtained from the Bay of Bengal and Monsoon Experiment
(BOBMEX). The cumulus convection though being a small-scale phenomenon, still influences its embedding environment by interaction
through various scales. This study shows the variation in the kinematic and convective parameters during the transition from
suppressed to active periods of convection. Convergence in the lower levels and strong upward vertical velocity, significant
during active convection are associated with the formation of monsoon depressions. The apparent heat source due to latent
heat release and the vertical transport of the eddy heat by cumulus convection, and the apparent moisture sink due to net
condensation and vertical divergence of the eddy transport of moisture, are estimated through residuals of the thermodynamic
equation and examined in relation to monsoon activity during BOBMEX. 相似文献
14.
The aim of this paper is to study the feasibility of deriving vertical wind profiles from current satellite observations.
With this aim, we carried out complex empirical orthogonal function (CEOF) analysis of a large number of radiosonde observations
of wind profiles over the Indian Ocean during the monsoon months. It has been found that the first two CEOFs explain 67% of
the total variance in wind fields. While the first principal component is well correlated with the winds at 850 mb (r = 0:80), the second one is highly correlated with winds at 200 mb (r = 0:89). This analysis formed the basis of a retrieval
algorithm which ensures the retrieval of vertical profiles of winds using satellite tracked cloud motion vector winds. Under
the assumption that accurate measurements of wind are available at the above mentioned levels, the r.m.s. error of retrieval
of each component of wind is estimated to range between 2 ms-1 and 6 ms-1 at different levels, which is much less than the natural variance of winds at these levels. For a better visualization of
retrieval, we have provided retrieved and true wind profiles side by side for four typical synoptic conditions during the
monsoon season. 相似文献
15.
Fluxes of heat, momentum and the kinetic energy over the arid and semiarid regions of Indian Peninsula have been computed.
Spectral analysis of these fluxes at 50 mb interval were performed at each level in the vertical up to 300 mb surface. The
eddy latent heat transport is governed essentially by short- and long-range periodicities. A 5-day periodicity is generally
present in the vertical mean eddy fluxes. Long-range periodic oscillations are more pronounced in the extreme north of the
Indian subcontinent. Dominance of medium-range periodicity is observed in all the fluxes except latent heat. 相似文献
16.
松辽盆地深层是由30多个孤立的断陷组成的断陷群,火山岩气藏是深层勘探的主要气藏类型。以断陷盆地火山岩大气田形成条件为主线,从深层断陷形成的特征分析着手,通过剖析控源及控藏因素,总结断陷盆地大气田形成条件。指出NNE-NE和NNW-NW两组控陷断裂体系共同控制深层断陷群的形成和展布,断陷沿控陷断裂方向呈带状展布。断陷内火山机构具有明显受断裂控制的不对称特征,沿断裂走向呈条带状分布。每个断陷通常由一个或多个断槽组成,断槽控制烃源岩的分布并自成含气系统,生烃断槽和火山岩在空间的有利配置是形成气藏的关键。环槽富集是深层断陷火山岩气藏最基本的规律,由于断裂控制了断陷、断槽、火山岩的形成分布,改善了油气运聚的通道条件,紧邻生烃断槽的断裂构造带是断陷内天然气有利富集区带;因此深部断裂控制了断陷火山岩气田的区域分布。勘探实践更进一步证明：对于断陷湖盆油气勘探,生烃主断槽是评价和勘探的关键单元;只要生烃断槽优质烃源岩发育,烃源岩与火山岩空间配置关系有利,对于“小而富”的中小型断陷(面积小于3 000 km2),也可以形成火山岩大气田(探明地质储量大于300×108 m3),这些认识推进了勘探思路由寻找大湖盆大断陷到寻找生烃主断槽的转变。 相似文献
17.
Fourier analysis has been used for the monthly mean northern hemispheric geopotential height for the levels 700 mb and 300 mb for the months April through August in bad monsoon years (1972, 74 and 79) and in years of good monsoon rainfall over India (1967, 73, 77). From the Fourier coefficients the transport of momentum and of sensible heat have been computed in wave number domain. Waves 1 to 3 show contrasting features during years of good monsoon and bad monsoon. Northward transport of momentum across subtropical latitudes is larger in good monsoon years, while northward transport of sensible heat is larger in bad monsoon years. In good monsoon years there is a large divergence of momentum in the subtropics while there is a large convergence of momentum in the mid-latitudes. In bad monsoon years there is a large divergence of sensible heat in the sub-tropics, but a large convergence in the mid-latitudes. These quantities show similar features in pre-monsoon (April to May) during good and bad monsoon years. 相似文献
18.
滇东南丘北区峰丛—洼地地貌形态特征分析 总被引：1，自引：0，他引：1
云贵高原东南部丘北区为峰丛—洼地岩溶组合地貌。利用统计分析方法考察了该区48个岩溶洼地及峰体的形态参数特征;利用分形理论方法计算了不同高程的等高线和地表水系的分维数。结果表明:（1）洼地的平均边数为5.6,平均周长3.4km,平均面积0.8km2;（2）洼地的加深和扩大近于同步,原始地面对后期溶蚀面的发育起控制作用;（3）峰丛—洼地的形态分形特征对岩溶演化具有很好的响应关系,可溶岩区等高线分维数平均为1.30,非可溶岩区为1.16,地表水文网分维数为1.07,反映岩溶区地形变化复杂,地下水文网较发育,岩溶发育程度较高;（4）研究区岩溶发育仍处于幼年至壮年期,将继续缓慢发育。 相似文献
19.
A steady state model of the Somali current including forcing by both the curl and the divergence of the wind stress is discussed.
The model equations are linear, but the results presented are for the one nonlinear case. The grid resolution was 12 km in
the zonal and 24 km in the meridional direction. The streamfunction and velocity potential of the current are presented for
forcing by divergence and compared with a situation when only the curl is present. The results indicate that a two-gyre system
appears in July, a representative month for the summer monsoon, only when divergence is included. Computations with available
data indicate that the divergence is comparable in magnitude to the curl near the location of the Somali current. The model
produces three other important features: (i) strong upwelling off the east coast of Africa, (ii) downwelling over central
Arabian sea and (iii) a strong eastward current in the upper layer towards the interior of the Arabian sea near 12°N. 相似文献
20.
V. A. Golubev 《Doklady Earth Sciences》2010,433(2):1083-1087
A comparison between values of thermal flux and the deep temperatures calculated by them and the depths of earthquake sources
in three areas of the Baikal Rift Zone is made. It has been shown that during transit from the Baikal depression to the adjacent
mountain massif, the thermal flux decreases almost 2–3 times. The corresponding deep temperatures decrease to a similar degree.
The available data for these areas on earthquake depths show that their lower boundary both beneath the depression and the
massif is located at almost the same depth, which is about 20 km. In this paper, the conclusion is made that the cause of
the absence of an interrelation between thermal and seismic fields lies in the discrepancy between the measured values of
thermal flux and its deep values. This discrepancy arises because conductive heat transfer in the upper part of the Earth’s
crust, up to 5–10 km depth, is highly distorted by heat-and-mass transfer of ground waters. In the middle part of the crust,
the difference in temperatures beneath depressions and ridges is leveled horizontally, which is reflected in almost the same
depth for the basement of the seismogenerating layer beneath these main rift structures. 相似文献