Title of the
Study: A Study of the Variation of Thunderstorm Activity over Sri
Lanka
Investigator(s): K.R. Abhayasinghe Bandara
Scientific background and
scope/objectives of the study:
Weather parameters (rainfall, temperature, pressure etc)
related to any place of the globe show variation in the time and aerial scales.
The magnitude of the variation differs from parameter to parameter. Lightning
activity, like rainfall, significantly vary in all scales and it is natural.
Increase of the global temperature particularly after the
industrial era, has a number of impacts on climate leading to changes globally
and locally. Lightning activity at any particular place may have been affected
by the global warming and the climate change during the past few decades. In
estimating the trend of change of lightning activity, an understanding of the
variation of lightning activity during the past is essential.
Lightning usually can be seen from distant places from the
place of its occurrence. For this reason observation of lightning alone is not
good enough to be considered in drawing the conclusions of the lightning
phenomenon. But thunder is heard well within about 20 km of the lightning flash
that caused thunder. Therefore, observation of thunder is regarded as the best
manual observation for existence of lightning in an area.
Objectives of the Study:
·
studying the variation of lightning
activity during different periods of the day (three-hour periods, morning,
afternoon, evening and night),
·
studying variation
of lightning activity on annual basis and variation of lightning activity on
decadel basis and
·
preparing thunder-day
contour maps for each decade during 30-year period 1970-1999.
Experimental Method:
The synoptic observation, including thunder activity at meteorological stations are entered in the Rough Observation Books (ROB) which are available for reference. Data of thunder activity for the 30-year period 1970-1999, from all 22 stations were collected and saved in excel files. Total number of annual thunder days during the period was counted and the average number of thunder days per year was then computed. Annual total thunder days of these stations during the period with data were plotted and trend lines were drawn.
The average number of thunder
days were plotted in a Sri Lanka map and contours were drawn to prepare the
isoceraunic map for Sri Lanka for the
period 1970-1999.
Results Obtained and
Conclusions:
· Annual lightning activity shows considerable variation from year to year.
· Lightning activity had an increasing trend in Ratnapura, Maha Iluppallama, Colombo, Galle, Katugastota, A’Pura, Kurunegala, Badulla and Trincomalee areas and decreasing trend in N’Eliya, Puttalam, Hambantota, Batticaloa, Ratmalana, Mannar, Katunayaka, Vavuniya, and Bandarawela areas.
· The maximum lightning activity has confined to Bandarawela area and the minimum activity over extreme north and in extreme southeastern areas during 1970-1999.