In this study, we present an assessment of the Conformal Cubic Atmospheric Model (CCAM) 50 km simulations forced by the sea surface temperature and sea ice concentration of six global climate models ...(GCMs) (ACCESS1-0, CCSM4, GFDL-CM3, NorESM, MPI-ESM and CNRM-CM5) from the Coupled Model Inter-comparison Project Phase 5 (CMIP5) over South Asia, centred on Sri Lanka. The model simulations were compared with the data provided by the Asian Precipitation Highly Resolved Observational Data Integration towards Evaluation of Water Resource (APHRODITE) project and ERA-Interim from the European Centre for Medium range Weather Forecast (ECMWF) over a broad region centred on Sri Lanka. This broad region includes South Asia and northern Indian Ocean. Statistical measures such as pattern correlations, mean biases and root mean square errors were calculated separately for the four seasons. Results based on statistical tests indicate that the current CCAM simulations capture the spatial patterns of 10 m wind speed, mean sea level pressure, temperature and rainfall over a broad region over South Asia fairly well. The annual cycles of temperature and rainfall were also compared against observations over the northern and southern regions of Sri Lanka by taking the field average of each model and the observed data. The characteristics of the observed annual variations of rainfall and temperature over the smaller domains are not very well captured by the CCAM simulations. There are differences in the magnitudes of the temperature and rainfall in the six member CCAM simulations. Comparatively, the two CCAM simulations CNRM-CM5 and GFDL-CM3 show slightly better agreement over the Sri Lankan region.
In this study, an analysis of century scale climate trends in the central highlands of Sri Lanka is presented. Monthly rainfall and temperature records of the period 1869–2006 from five ...climatological stations were analyzed. The trend is calculated by the least square regression analysis and the significance of the observed trend is estimated using the Mann–Kendall statistic. The results clearly show that there is a statistically significant decrease in annual rainfall in the western slopes of the central highlands. Throughout the last century, the annual reduction of rainfall in Nuwara Eliya which is at an altitude of 1895 m was 5.2 mm/year. The decrease is largely due to the reduction in southwest monsoon rainfall which contributes to 75% of the total reduction. No significant change was observed on the eastern side of the central highlands which receives rainfall predominantly from the northeast monsoons. The mean annual temperature in the mountainous region shows a uniform increasing trend which is in line with the 100-year global temperature increase of 0.8 ± 0.2
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C. Kandy, which is at an altitude of 477 m and closely linked with the rainfall climatology of Nuwara Eliya, showed no significant change in the mean annual temperature. If the current trend continues, in another 100 years, western and eastern slopes of central highlands will receive the same amount of rainfall from the southwest monsoon and the northeast monsoon which will have far reaching consequences for Sri Lanka’s economy and the ecology of the hill country.
A detailed study on electric field characteristics of Narrow Bipolar Pulses (NBP) observed in Sri Lanka is presented here. NBPs analyzed in this work were recorded at a coastal location in the ...Southern part of Sri Lanka (Matara: 5.95 °N, 8.53 °E), from five highly active consecutive thunderstorm days during the month of May in 2013. The waveforms were recorded with a 10ns resolution within a 100ms time window. Both positive and negative NBPs were observed in this study with the negative type being the most frequent. Parameters presented in this study were the rise time (Tr), zero crossing time (Tz), the duration of slow front (Ts), the full width of half maximum (FWHM), the pulse duration and the ratio of amplitude of overshoot to the corresponding peak amplitude (Os/Pa). The corresponding average values of negative NBPs for these parameters were found to be 0.58µs, 3.01µs, 0.20µs, 1.38µs, 19.21µs and 0.19 respectively. Similarly, for positive events corresponding values were 1.38µs, 4.66µs, 0.48µs, 1.93µs, 16.42µs and 0.37 respectively. The above values conforms to a much narrower bipolar events when compared to previously reported values which is considered to be caused by the propagation effects of signals captured by the apparatus.
•Temporal features of Narrow Bipolar events of both polarities were studied.•The dominant polarity recorded was of the negative type with a percentage of 78.•Majority of the pulses were very narrow.•Nearly one third in magnitude when compared to historic studies of both polarity.•Narrowness is considered to be due to minimal propagation effects on the signal.
ABSTRACT
The onset, retreat and the length of growing season in the north‐eastern region of Sri Lanka were investigated using daily rainfall data for the period 1961 to 2000. Data from three weather ...stations situated in the coastal belt in the northern and eastern parts of Sri Lanka (Jaffna, Trincomalee and Batticaloa) that receive rainfall predominantly from the northeast monsoon were selected for this study. A method based on cumulative rainy days was utilized in the determination of the onset and retreat dates. It is shown that there is substantial interannual variability in onset and retreat dates. The mean onset and retreat dates fall on the standard week 38.3 ± 2.7 and 53.0 ± 2.9, respectively. The mean duration of the growing season is 14.7 ± 3.4 weeks. The retreat date and thus the length of growing season could be extended by 2 weeks if the probability of occurrence of rain during the onset is favourable for the retreat. The results indicate that there has been no significant trend in the onset and retreat dates during the last 40 years in the dry zone of Sri Lanka. The onset date and the length of growing season are weakly correlated with early onset dates leading to longer growing seasons. The study concludes that rainy days could be used successfully to determine the mean rainfall onset and retreat dates in the dry zone of Sri Lanka.
Channel brightness of 500 mm long electrical discharges were measured by analyzing a set of digitized images taken by 3 cameras placed symmetrically around a discharge gap at a radial distance of 200 ...cm from the axis of the spark. The sparks were generated between a steel rod and a plane electrode. The distribution of the brightness across the channel represented a Gaussian distribution. A linear correlation was seen between the channel brightness measured by different cameras looking at the same spark channel. No correlation was seen between the channel brightness and the channel depth (direction perpendicular to the camera plane). The measured peak current and the brightness of the main spark channel show a high degree of correlation (R 2 =0.97). The sum of brightness of branches was equal to the brightness of the parent channel. One can use this result to calculate the relative distribution of branch currents in complex electrical discharges including natural lightning flashes. If the current in the parent channel is known, branch currents can be calculated by measuring the optical intensities using photographic techniques.
The hypothesis that the wet and dry patterns of daily precipitation observed in Colombo can be modeled by a first order Markov chain model was tested using daily rainfall data for a 60-year period ...(1941–2000). The probability of a day being wet or dry was defined with respect to the status of the previous day. Probabilities were assumed to be stationary within a given month. Except for isolated single events, the model is shown to describe the observed sequence of wet and dry spells satisfactorily depending on the season. The accuracy of modeling wet spells is high compared to dry spells. When the model-predicted mean length of wet spells for each month was compared with the estimated values from the data set, a reasonable agreement between the model prediction and estimation is seen (within ±0.1). In general, the data show a higher disagreement for the months having longer dry spells. The mean annual duration of wet spells is 2.6 days while the mean annual duration of dry spells is 3.8 days. It is shown that the model can be used to explore the return periods of long wet and dry spells. We conclude from the study that the Markov chain of order 1 is adequate to describe wet and dry patterns of weather in Colombo.
Electric radiation fields produced by lightning cloud flashes have been analyzed using Fourier methods to obtain amplitude spectra for frequencies in the range of 20 kHz to 20 MHz. Time to thunder ...measurements were used to extract the distances to the cloud flashes from the measurement site. The spectra were generated by analyzing the first 10 ms time window of cloud flashes with 10 ns sampling resolution, and they show f -1 frequency dependence up to 2 MHz followed by f -2 dependence and higher for frequencies above 2 MHz. The results agree very well with previous measurements carried out for individual pulses produced by various lightning processes. By utilizing digital filters, it has been shown that measurements taken with narrowband filters agree with the results produced under wideband measurements
Event shapes for Au + Au collisions at 11.4 GeV/ital c per nucleon were studied over nearly the full solid angle with the E877 apparatus. The analysis was performed by Fourier expansion of azimuthal ...distributions of the transverse energy (ital Esub ital T) measured in different pseudorapidity intervals. For semicentral collisions a pronounced event anisotropy is identified with a clear forward-backward anticorrelation. In the forward pseudorapidity interval up to 9% of the ital Esub ital T is in a directed component. The signal decreases for peripheral and very central collisions.
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