Evaluation of Forecast Performance of an Economical Explicit Time Integration Scheme in a Limited Area Model over Indian Region

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Application of the telluric and magnetotelluric methods in selection of sites for nuclear plants

The paper deals with the application of the telluric method and of magnetotelluric soundings including experimental and model data on the localization of tectonic disturbances in connection with the selection of appropriate sites for nuclear plants.     

斜压半地转模式中的非频散周期解

给出了３个通量矢量，从而将非线性平流项表示为３个通量矢量的旋度和散度，它们分别对纬向风和经向风的低频加速产生贡献。经过卷积运算，还建立了低频变化的动力学模型。给出了通量矢量Ｅ．、Ｇ１．、Ｇ２．等的空间分布及其相应的流函数与势函数的水平分布和时间演变，从而指出，瞬变扰动间的相互作用对流动具有低频加速作用。     

Baroclinic energetics and zonal plane distribution of monsoon disturbances

The adiabatic, quasi-geostraphic, 25-layer, numerical, linear model with Ekman boundary layer friction is utilised to perform the baroclinic stability analysis of the mean monsoon zonal wind profile. It is shown thec _i is a function of the resultant wavenumber alone. This relation is able to explain the effects of the lateral walls on the unstable waves.The energetics and zonal plane distribution of the short and long preferred viscous waves are computed. The upward motion of the short wave together with the warm (cold) core lies to the west of the surface trough position above (below) 850 mb. Further, it is shown that the main source of kinetic energy for the wave lies in the middle layer (850–700 mb) which is transported to the lower and upper layers. Computed is found to be in good agreement with observed values.     

Results of the studies of monsoon circulation with radon as a tracer

Radon-222 activity levels have been measured at deck level in regions of the Arabian Sea, Indian Ocean, and Bay of Bengal during the summer monsoon periods of 1973, 1977, and 1979, as part of the Monex programme. The aim of the measurements was to find the source regions of the monsoon air and the variations in its composition under different synoptic conditions. The radon data confirm that the monsoon air is predominantly of southern-hemisphere origin, with a small continental component. The continental component, as indicated by radon values, increases at higher latitudes and seems to vary with different circulation patterns in the synoptic scale. The use of radon as a tracer in monsoon studies is thus demonstrated.     

Total ozone response to major geomagnetic storms and changes in meteorological situations

Summary The total ozone response to strong major geomagnetic storms (A_p≥60) in winter along the 50° N latitudinal circle is studied. The results add to the recent results of Laštovička et al. (1992) obtained for European middle latitudes (∼50°N) and to the results of Mlch (1994). A significant response of total ozone is only observed in winter under high solar activity/E-phase of QBO conditions (E-max) and seems to be caused by geomagnetic storm-induced changes of atmospheric dynamics. There are two sectors along latitude 50°N, which are sensitive to forcing by geomagnetic storms both in total ozone and the troposphere — north-eastern Atlantic-European and eastern Siberia-Aleutian sectors. The total ozone response under E-max conditions manifests itself mainly as a large decrease in the longitudinal variation of ozone after the storm, which means an increase of ozone in Europe. The observed effects in total ozone consist in redistribution, not production or loss of ozone.     

Meridional transport of sensible heat in contrasting monsoon activity: Spherical harmonic analysis

Spherical harmonic analysis is made of the grid point values of geopotential heights at 700 mb and 300 mb levels for the months April to August for the years 1967 and 1972. The year 1967 is a good monsoon year and 1972 is a bad monsoon year in India. Meridional transport of sensible heat is obtained in wave number domain using spherical harmonic coefficients at 500 mb level form=1 to 10 andn–m=0 to 10, wherem represents the wave number round the globe andn–m gives the numbers of zero points from north pole to south pole excluding the poles themselves.Large northward transports of sensible heat in the month of May and in the monsoon months at the subtropics are characteristic of bad monsoon. Wave 1 transports sensible heat southward (forn–m=0) and wave 2 transports sensible heat northward (forn–m=4). Strengthening of wave 1 is conducive to good monsoon year and strengthening of wave 2 is conducive to bad monsoon year. These are the same features obtained in Fourier analysis. The contrasting features exist in waves 1 and 2 both in good and in bad monsoon and are better defined in the present analysis than in the Fourier analysis of the earlier study. However, waves 1 and 2 reveal clearer contrast in the present analysis than in the Fourier analysis. Bad monsoon activity is associated with large divergence of heart at subtropics and large convergence of heat at extra tropics.     

Water vapour transport of the pre-monsoon period and the general performance of the Indian summer monsoon

The advective monthly mean transfer of water vapour in the layer below 700 mbar is investigated for India for the years 1962 to 1972 and for the months January to September. The average zonal and meridional components of the transfer of water vapour for India are obtained. They are further averaged for different combinations of the pre-monsoon months from January to May and are correlated with the summer monsoon rainfall. The correlation coefficients for zonal transfer of water vapour are either negative or small positive for different combinations of the months mentioned above. The correlation coefficients for the meridional transfer of water vapour are positive. The maximum value is 0.74 for the March to May combination and is statistically significant at the 1% level.An extensive investigation is, therefore, made for the March to May averages of water vapour transfer for four broad regions of India. The parameters of water vapour transfer for these regions are compared with the threshold values and the prediction category, normal or drought, for the subsequent summer monsoon season is determined for all years. The correlation coefficient between the index of drought, as determined from parameters of water vapour transport and rainfall departure, is statistically significant at the 2% level.     

Link between convection and meridional gradient of sea surface temperature in the Bay of Bengal

We use daily satellite estimates of sea surface temperature (SST) and rainfall during 1998–2005 to show that onset of convection over the central Bay of Bengal (88–92°E, 14–18°N) during the core summer monsoon (mid-May to September) is linked to the meridional gradient of SST in the bay. The SST gradient was computed between two boxes in the northern (88–92°E, 18–22°N) and southern (82–88°E, 4–8°N) bay; the latter is the area of the cold tongue in the bay linked to the Summer Monsoon Current. Convection over central bay followed the SST difference between the northern and southern bay (ΔT) exceeding 0.75°C in 28 cases. There was no instance of ΔT exceeding this threshold without a burst in convection. There were, however, five instances of convection occurring without this SST gradient. Long rainfall events (events lasting more than a week) were associated with an SST event (ΔT ≥ 0.75°C); rainfall events tended to be short when not associated with an SST event. The SST gradient was important for the onset of convection, but not for its persistence: convection often persisted for several days even after the SST gradient weakened. The lag between ΔT exceeding 0.75°C and the onset of convection was 0–18 days, but the lag histogram peaked at one week. In 75% of the 28 cases, convection occurred within a week of ΔT exceeding the threshold of 0.75°C. The northern bay SST, T _N , contributed more to ΔT, but it was a weaker criterion for convection than the SST gradient. A sensitivity analysis showed that the corresponding threshold for T _N was 29°C. We hypothesise that the excess heating (∼1°C above the threshold for deep convection) required in the northern bay to trigger convection is because this excess in SST is what is required to establish the critical SST gradient.     

Ionospheric effetcs of an intense geomagnetic storm

An investigation of the response of the mid-high, mid and low latitude critical frequency foF2 to the geomagnetic storm of 15 July 2000 is made. Ground-based hourly foF2 values (proportional to square root of peak electron density of F2-layer) from four chains of ionospheric stations located in the geographic longitude ranges 10°W–35°E, 60°E–120°E, 130°E–170°E, 250°E–295°E are used. Relative deviations of foF2 are considered. The main ionospheric effects for the considered storm are: long-duration negative disturbances at mid-high latitudes in summer hemisphere in sectors where the storm onset occurred in the afternoon/night-time hours; short-duration positive disturbances in the summer hemisphere at mid-high latitudes in the pre-sunset hours during the end of main phase-first stage of the recovery; small and irregular negative disturbances in the low latitude winter hemisphere which predominate during the main phase and first part of the recovery, and positive disturbances in both hemispheres at mid-high and mid latitudes prior to the storm onset irrespective of the local time. In addition, the validity of some physical mechanisms proposed to explain the F2 region behaviour during disturbed conditions is considered. gus-mansilla@hotmail.com