A study of evening convective clouds over Kochi and neighbourhood

Radar echoes of 0900 and 1100 UTC over Kochi and 200 km around were studied from 1996 to 1999 along with SST of southeast Arabian Sea and Kochi. The following results are obtained : Monsoon convective cloud tops were lower than Pre-monsoon and Post-monsoon convective cloud tops. (ii) In the mean, monsoon cloud tops gradually increased from 1996 to 1998 and then decreased. (iii) Very large convective activity existed during August 1997 to June 1998 compared to other periods of this study. Seasonally the higher the SST, the higher is convective cloud top. (v) Interannually, large positive SST anomaly coincided with high convective activity and this may be related to then prevailing El Nino.

Use of SWIRLS nowcasting system for quantitative precipitation forecast using Indian DWR data

Local severe storms are extreme weather events that last only for a few hours and evolve rapidly. Very often the mesoscale features associated these local severe storms are not well-captured synoptically. Forecasters have to predict the changing weather situation in the next 0-6 hrs based on latest observations. The operational process to predict the weather in the next 0-6 hrs is known as “nowcast”. Observational data that are typically suited for nowcasting includes Doppler Weather Radar (DWR), wind profiler, microwave sounder and satellite radiance. To assist forecasters, in predicting the weather information and making warning decisions, various nowcasting systems have been developed by various countries in recent years. Notable examples are Auto-Nowcaster (U.S.), BJ-ANC (China-U.S.), CARDS (Canada), GRAPES-SWIFT (China), MAPLE (Canada), NIMROD (U.K.), NIWOT (U.S.), STEPS (Australia), SWIRLS (Hong Kong, China), TIFS (Australia), TITAN (U.S.) (Dixon and Wiener, 1993) and WDSS (U.S.). Some of these systems were used in the two forecast demonstration projects organized by WMO for the Sydney 2000 and Beijing 2008 Olympic. A common feature of these systems is that they all use rapidly updated radar data, typically once every 6 minutes.The nowcasting system SWIRLS (“Short-range Warning of Intense Rainstorms in Localized Systems”) has been developed by the Hong Kong Observatory (HKO) and was put into operation in Hong Kong in 1999. Since then system has undergone several upgrades, the latest known as “SWIRLS-2” to support the Beijing 2008 Olympic Games. SWIRLS-2 is being adapted by India Meteorological Department (IMD) for use and test for the Commonwealth Games 2010 at New Delhi with assistance from HKO. SWIRLS-2 ingests a range of observation data including SIGMET/IRIS DWR radar product, raingauge data, radiosonde data, lightning data to analyze and predict reflectivity, radar-echo motion, QPE, QPF, as well as track of thunderstorm and its associated severe weather, including cloud-to-ground lightning, severe squalls and hail, and probability of precipitation. SWIRLS-2 uses a number of algorithms to derive the storm motion vectors. These include TREC (“Tracking of Radar Echoes by Correlation”), GTrack (Group tracking of radar echoes, an object-oriented technique for tracking the movement of a storm as a whole entity) and lately MOVA (“Multi-scale Optical flow by Variational Analysis”). This latest algorithm uses optical flow, a technique commonly used in motion detection in image processing, and variational analysis to derive the motion vector field. By cascading through a range of scales, MOVA can better depict the actual storm motion vector field as compared with TREC and GTrack which does well in tracking small scales features and storm entity respectively. In this paper the application of TREC and MOVA to derive the storm motion vector, reflectivity and QPF using Indian DWR data has been demonstrated for the thunderstorm events over Kolkata and New Delhi. The system has been successfully operationalized for Delhi and neighborhood area for commonwealth games 2010. Real time products are available on IMD website

Sector wise echoes study and climatology around Jaisalmer

The capability of Weather Radar to see through the thunder clouds and rain has made it a unique observation tool for remotely surveying the atmosphere. Pulsed radar technique has been applied with remarkable success to map the rain field of various duration and intensities along with movement of storms in real time within the effective detection range of radar. It is a very good tool for forecaster to provide better warning for impending storms and heavy rainfall over the area under radar surveillance and thereby losses due to storm can be minimized while their benefits can be continued like water resource management. In the present work attention has been focused on conducting a comprehensive study of frequencies of occurrence of echoes around Jaisalmer up to 200 km from radar site and the surrounding of it has divided into four equal sectors, i.e., sector-1 (NW, 270°-360° ) , sector-2 (NE, 0°-90°) , sector-3 (SE, 90°-180° ) and sector-4 (SW, 180°-270°). Total number of echoes under the study was 28918 for the period from 19th April, 1993 to 31st December, 2010. Total number of echoes analyzed in Sector-1, were 5441(18.8%), in sector-2, number of echoes analyzed were 9554(33.0%), in sector-3, number of echoes analyzed were 9479 (32.8%) and in sector-4, number of echoes analyzed were 4444(15.4%). Radar echoes to be classified month-wise and the lowest number of average echoes observed in the month of December was 0.4%, in the month of November 0.5%, in October and March 1.6% and in the month of January and February 2.0% .The highest number of annual average echoes observed in the month of July was 30.1% followed by August 24.6%, June 17.2%, May 8.3%, April 6.3% and September 5.8%. Height wise echoes analyzed and the highest number of echoes found for 3 km in all the four sectors were 29.0% and the lowest were for 16 km as 0.2%.

Near-Field Route Optimization-Supported Polar Ice Navigation via Maritime Radar Videos

The accurate design of ship routing plans in arctic areas is not easy, considering that navigation conditions (e.g., weather, visibility, and ice thickness) may change frequently. A ship’s crew identifies sea ice in arctic channels with the help of radar echoes, and ship maneuvering decisions are made to avoid navigation interference. Ship officials must manually and consistently change the ship’s route of travel, which is time-consuming and tedious. To address this issue, we propose a near-field route optimization model for the purpose of automatically selecting an optimal route with the help of radar echo images. The ship near-field route optimization model uses a multiobjective optimal strategy considering factors of minimum navigation risk and steaming distance. We verified the model’s performance with the support of the Xuelong voyage dataset. This research finding can help a ship’s crew to design more reasonable navigation routes in polar channels.

Remote Sensing of the Polar Ice Zones with HF Radar

Radars operating in the HF band are widely used for over-the-horizon remote sensing of ocean surface conditions, ionospheric studies and the monitoring of ship and aircraft traffic. Several hundreds of such radars are in operation, yet only a handful of experiments have been conducted to assess the prospect of utilizing this technology for the remote sensing of sea ice. Even then, the measurements carried out have addressed only the most basic questions: is there ice present, and can we measure its drift? Recently the theory that describes HF scattering from the dynamic sea surface was extended to handle situations where an ice cover is present. With this new tool, it becomes feasible to interpret the corresponding radar echoes in terms of the structural, mechanical, and electrical properties of the ice field. In this paper we look briefly at ice sensing from space-borne sensors before showing how the persistent and synoptic wide area surveillance capabilities of HF radar offer an alternative. The dispersion relations of different forms of sea ice are examined and used in a modified implementation of the electromagnetic scattering theory employed in HF radar oceanography to compute the corresponding radar signatures. Previous and present-day HF radar deployments at high latitudes are reviewed, noting the physical and technical challenges that confront the implementation of an operational HF radar in its ice monitoring capability.

Distribution of the areas and heights of the radar echoes from convective clouds around Delhi during monsoon season

Distributions of areas and heights of radar echoes from convective clouds, observed in Delhi region during six monsoon seasons, 1967-1972, were studied. Stratification of the echoes according to their areas into three different scales, namely scale D scale(<100 km2), C scale (101-1000 km2) and B/C scale (> 1000 km2) indicated predominance of the echoes in D scale, with relatively small percentage in. C and B/C scales. Frequency distributions of areas and heights of these echoes tended to be lognormally distributed.