7.   Roy Bhowmik, S. K. and K. Prasad (2008): Improving IMD operational Limited Area Model forecasts. Geofizika, 25, 87-108. 

 

ABSTRACT:

  

         India Meteorological Department (IMD) has been using a Limited Area Model (LAM) on operational basis for the forecast up to 48 hours with the first guess fields for objective analysis and lateral boundary conditions from the global spectral model (T–80) run of the National Center for Medium Range Weather Forecasting (NCMRWF), New Delhi. In this paper the model code has been modified and made more flexible, delinking it from the NCMRWF (T–80). This has allowed the use of initial and boundary conditions directly from the NCEP Global Forecast System (GFS) products available at the resolution of 1° x 1° lat./long. The main interest in this study is to improve the analysis and forecast in the short range time scale (up to 72 hours) by improving the model (LAM) resolution and using better Initial and boundary conditions from the NCEP GFS instead of the NCMRWF T–80 model. Simulation experiments are performed on wide variety of synoptic situations which occur very often over the Indian sub-continent. The performance evaluation in terms of qualitative comparison between the model simulated outputs against actual observations and the outputs of the operational model indicates that the modified version of the model is capable to provide a improved numerical guidance on the occurrence of heavy rainfall in the 48–72 hours forecast scale.

 

Keywords: Limited Area Model, monsoon depression, first guess, lateral boundary condition.

 

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8.   Mahmud, M. and  T. S. V Vijaya Kumar (2008): Forecasting severe rainfall in the equatorial Southeast Asia. Geofizika, 25, 109-128.

 

ABSTRACT:

           

          Accurate prediction of monsoon heavy rainfall events in the equatorial region has always been a challenge to weather forecasters. In this paper, forecast of a severe precipitation event that occurred over the eastern central coast of Peninsular Malaysia was attempted using the state-of-the-art Florida State University (FSU) Global and Regional Spectral Models. The sensitivity of parameterized convection in these models on precipitation forecast skill is studied using two different parameterization schemes for cumulus convection (the Relaxed Arakawa-Schubert scheme and the modified Kuo scheme). Low precipitation threshold of rainfall less than 2 mm day^–1 was successfully predicted by both versions of the FSU model. However, the convection schemes lacked skill in predicting the correct placement of the area and amount for the high precipitation threshold greater than 40 mm day–1. Further evaluation of the predictive skills showed that the Relaxed Arakawa-Schubert scheme was a consistently better predictor of rainfall due to its low bias and lower root mean square errors (RMSEs) compared to the modified Kuo parameterization scheme.

 

Keywords: monsoon rainfall, equatorial Southeast Asia, global and regional spectral models, rainfall prediction.

 

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9.   Mazzocco Drvar D. and V. Jurčec (2008): High resolution isentropic model applied to local weather forecasting. Geofizika, 25, 129-138. 

 

ABSTRACT:

           

          To our dear friend, mr. sc. Dražen Glasnović who was an exceptional research scientist. He left too soon taking his great ideas with him. Nevertheless, his priceless work will keep us going and he will never be forgotten.

          This paper is primarily devoted to general discussion of HRID (High resolution isentropic diagnosis) model developed by Glasnović (1983) and its vertical time cross-sections used operationally on direct output of forecasting model ALADIN (Aire Limitee Adaptation Dynamique et Development International). HRID is based on polynomial hydrostatic adjustment technique making use of reciprocal value of thermal stability parameter and its higher order derivatives. Since these relations are applied in local points of vertical interpolation, the problem is considered analytically, eliminating the finite difference approximation procedure in layers with different isentropic thicknesses. This paper presents a local 72 hourly ALADIN/HRID forecast for the city of Split, Croatia, at the eastern Adriatic coast, with detailed vertical atmospheric structure indicating the characteristic features of a frontal passage on 2 January 2007.

 

Keywords: ALADIN, HRID, objective analysis, vertical cross-sections.

 

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10.   Kotal, S. D., S. K. Roy Bhomwik and P. K. Kundu (2008): Application of statistical - dynamical scheme for real time forecasting of the Bay of Bengal very severe cyclonic storm "SIDR" of November 2007. Geofizika, 25, 139-158.

 

ABSTRACT:

 

          There is an operational requirement to formulate an objective procedure to handle operational cyclone forecasting work in a more efficient and effective way. In this paper we propose a four-step statistical-dynamical scheme for the real time application in cyclone forecasting work. The four-step scheme consists of (a) Analysis of Genesis Potential Parameter (GPP), (b) Estimation of Maximum Potential Intensity (MPI), (c) 72 hours Intensity Prediction and (d) Prediction of decaying intensity after the landfall. In November 2007, a very severe cyclonic storm 'SIDR' formed over the Bay of Bengal and hit the Bangladesh coast. In this paper, a four-step procedure is demonstrated for real time forecasting this cyclone. The results show that the GPP analysis at early stages of development can strongly indicate that the cyclone »SIDR« had enough potential to reach its cyclone stage. The MPI of the cyclone based on the SST (Sea Surface Temperature) values along the cyclone track is estimated to be 146 knots. The observed maximum intensity of the cyclone is found to be 79 % of its MPI. The 72 hours intensity prediction based on 00 UTC on 12 November could reproduce the intensity value of 109 knots, an underestimation of 6 knots. The subsequent updated forecasts are found to be realistic and useful. The 6-hourly decaying intensity forecast after the landfall shows an underestimation of 10 knots at 12 hours forecast and a significant improvement is noticed with the incorporation of correction factor. The study has documented the potentiality of the procedure for operational application.

 

Keywords: Tropical cyclone, Statistical-Dynamical Scheme, Genesis Potential Parameter (GPP), Maximum Potential Intensity (MPI), Intensity Prediction (IP), Decay after Landfall (DAL), Bay of Bengal.

 

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11.    Narkhedkar, S. G., S. K. Sinha and A. K. Mitra (2008): Mesoscale objective analysis of daily rainfall with satellite and conventional data over Indian summer monsoon region.        Geofizika, 25, 159-178.

 

ABSTRACT:

 

          A mesoscale objective analysis scheme for producing daily rainfall analysis on a regular latitude/longitude grid over the Indian monsoon region is described. The Barnes scheme is applied to interpolate irregularly distributed daily rainfall data on to a regular grid. The spatial resolution of the interpolated arrays is 0.25 degrees of latitude by 0.25 degrees of longitude. Daily rainfall derived from INSAT IR radiances and raingauge observations are combined to produce this analysis. Some objectively determined constraints are employed in this study: (i) weights are determined as a function of data spacing, (ii) in order to achieve convergence of the analysed values three passes through the data are considered and there is automatic elimination of wavelengths smaller than twice the average data spacing. The case of a typical westward moving monsoon depression during the 1994 monsoon season is selected to represent the characteristics of the analysed rainfall. Objective analyses of six days (16 to 21 August 1994) have been carried out using Barnes three pass scheme. The weighting function scale length parameter (c, denominator in the exponential Gaussian weight function) is varied from over a range of values and the root mean square (rms) errors are computed to select the appropriate value of c. The value of c depends on the number of correction passes being performed and on the density of the observations. The characteristics of the output field from this analysis system have been examined by comparing the analysed rainfall with the observed values. The heavy rainfall over the Western Ghat of India has been clearly brought out in this analysis.

 

Keywords: mesoscale analysis, Barnes three pass scheme, rainfall analysis

 

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12.    Žabkar, R., J. Rakovec and S. Gaberšek (2008): A trajectory analysis of summertime ozone pollution in Slovenia. Geofizika, 25, 179-202.

 

ABSTRACT:

 

          Annual number of days with exceeded ozone threshold values at the ground level measuring stations in Slovenia ranges from a few days in the interior of the country to up to 25 days at the Mediterranean stations. The highest number of ozone exceedances is usually recorded in the southwestern part of Slovenia, close to the Adriatic Sea, where favorable meteorological conditions enhance ozone formation. Local emission sources in this part of the country cannot explain the measured level of pollution. In addition, high ozone concentrations are occasionally measured at some Slovenian rural sites. We performed an ozone analysis with respect to air mass origin to provide an insight into processes leading to the high measured values of near-ground ozone. Three dimensional back trajectories were computed with a 3 hour-time interval for four measuring sites in Slovenia, generating eight arrival times per day starting at 00 UTC, for the warm parts (April – September) of the years 2003 and 2004. Trajectory clustering was used to determine typical pathways of air masses. Ozone and basic meteorological characteristics of trajectory clusters were further analyzed and multiple comparison tests were applied to determine which pairs of clusters differ significantly in measured ozone. In addition, concentration weighted trajectory (CWT) and number density (ND) of »polluted trajectories« were calculated to provide additional information about possible emission source regions.

          Results suggest that high ozone concentrations appear most often in the short trajectory clusters of slow-moving air masses originated from SW. Moreover, CWT and ND fields confirm that high near-ground ozone levels in Slovenia are usually associated with trajectories originating from the area of the northern Adriatic Sea and its coastal regions. A heavily industrialized Po River Basin does not appear to have a significant direct impact on measured ozone concentrations in Slovenia, but may considerably contribute to the overall pollution over the northern Adriatic Sea together with coastal emissions.

 

Keywords: tropospheric ozone, trajectories, clustering, transport

 

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