Prof. Upul Sonnadara
Department of Physics
Journal Articles
A Markov chain probability model to describe wet and dry patterns of weather at Colombo
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.
Performance of lightning locating systems in extracting lightning flash characteristics
Performance of lightning locating systems in extracting lightning flash characteristics, U. Sonnadara, V. Kathriarachchi, V. Cooray, R. Montano and T. Gotschl, J. Atmospheric and Solar-Terrestrial Physics (2014)
Assessment of the Impacts of Sri Lanka’s Programme for School Improvement on Students’ Academic Progress
Assessment of the Impacts of Sri Lanka’s Programme for School Improvement on Students’ Academic Progress, H. Aturupane, P. Glewwe, R. Ravina, U. Sonnadara, S. Wisniewski, J. of Development Studies (2014)
Reconstruction of missing monthly temperature observations in Jaffna, Sri Lanka
Reconstruction of missing monthly temperature observations in Jaffna, Sri Lanka, A. Thevakaran and D.U.J. Sonnadara, J. National Science Foundation, 41 1 (2013) 23-30
Computer simulation of tree development with random variations and probabilistic growth of branches
Computer simulation of tree development with random variations and probabilistic growth of branches, K.D.S. Jinasena and D.U.J. Sonnadara, J. National Science Foundation, 41 3 (2013) 229-235
Study of Diurnal and Seasonal Wind Characteristics for Wind Resource Assessment
Study of Diurnal and Seasonal Wind Characteristics for Wind Resource Assessment, R.M. Weerasinghe, A.S. Pannila, M.K. Jayananda and D.U.J. Sonnadara, International Energy Journal, 13 4 (2012) 177-188
Fractal Nature of Simulated Lightning Channels
Fractal Nature of Simulated Lightning Channels, M.D.N. Perera and D.U.J. Sonnadara, Sri Lankan J. Physics, 13 2 (2012) 9-25
Traffic noise enhancement due to speed bumps
Traffic noise enhancement due to speed bumps, S.N. Wewelwala and D.U.J. Sonnadara, Sri Lankan J. Physics, 12 (2011) 17-23
Performance of neural networks in forecasting short range occurrence of rainfall
Performance of neural networks in forecasting short range occurrence of rainfall, V.S. Rathnayake, H.L. Premaratne and D.U.J. Sonnadara, J. National Science Foundation, 39 3 (2011) 251-260
A Simple Reconfigurable Microprocessor in a 36 Macrocell CPLD
A Simple Reconfigurable Microprocessor in a 36 Macrocell CPLD, W.A.S. Wijesinghe, M.K. Jayananda and D.U.J. Sonnadara, J. National Science Foundation, 39 3 (2011) 261-266
Simulation of Diffusion Limited Aggregation in Field Programmable Gate Arrays
Simulation of Diffusion Limited Aggregation in Field Programmable Gate Arrays, W.A.S. Wijesinghe, M.K. Jayananda and D.U.J. Sonnadara, J. National Science Foundation, 38 4 (2010) 213-218
Performance of neural network in forecasting daily precipitation using multiple sources
Performance of neural network in forecasting daily precipitation using multiple sources, H.D.P. Weerasinghe, H.L. Premaratne and D.U.J. Sonnadara, J. National Science Foundation, 38 3 (2010) 163-170
Predicting three-dimensional fractal dimensions of electrical discharges using two-dimensional projections
Predicting three-dimensional fractal dimensions of electrical discharges using two-dimensional projections, D. Amarasinghe and U. Sonnadara, J. Science, Eastern University of Sri Lanka, 6 (2009) 57-67
Measurement of noise within passenger trains on a coastal railway line
Measurement of noise within passenger trains on a coastal railway line, N.S. Pahalavithana and D.U.J. Sonnadara, Sri Lankan J. Physics, 10 (2009) 44-56
Performance of artificial neural networks for forecasting daily occurrence and annual depth of rainfall at a tropical site
Performance of a feed-forward back-propagation artificial neural network on forecasting the daily occurrence and annual depth of rainfall at a single meteorological station is presented. Both short-term and long-term forecasting was attempted, with ground level data collected by the meteorological station in Colombo, Sri Lanka (79° 52′E, 6° 54′N) during two time periods, 1994–2003 and 1869–2003. Two neural network models were developed; a one-day-ahead model for predicting the rainfall occurrence of the next day, which was able to make predictions with a 74·3% accuracy, and one-year-ahead model for yearly rainfall depth predictions with an 80·0% accuracy within a ± 5% error bound. Each of these models was extended to make predictions several time steps into the future, where accuracies were found to decrease rapidly with the number of time steps. The success rates and rainfall variability within the north-east and south-west monsoon seasons are also discussed.
Performance evaluation of multipliers in reconfigurable hardware
Performance evaluation of multipliers in reconfigurable hardware, W.A.S. Wijesinghe, M.K. Jayananda and D.U.J. Sonnadara, J. National Science Foundation, 36 3 (2008) 249-251
Modelling free flowing vehicular traffic noise
Modelling free flowing vehicular traffic noise, R.T. Sooriaarachchi and D.U.J. Sonnadara, Engineer, 40 2 (2008) 43-37
Fractal characteristics of simulated electrical discharges
Fractal characteristics of simulated electrical discharges, D.I. Amarasinghe and D.U.J. Sonnadara, J. of National Science Foundation, 36 2 (2008) 137-143
Detecting and preventing plagiarism in online assessment
Detecting and preventing plagiarism in online assessment, C.T. Wannige, D.U.J. Sonnadara, H.A. Usoof, K.P. Hewagamage, J. Science University of Kelaniya, 4 (2008) 95-104
Correlation between brightness and channel currents of electrical discharges
Correlation between brightness and channel currents of electrical discharges, D. Amarasinghe, U. Sonnadara, M. Berg, and V. Cooray, IEEE Transactions on Dielectrics and Electrical Insulations, 14 5 (2007) 115-1160
Channel tortuosity of long laboratory sparks
Channel tortuosity of long laboratory sparks, D. Amarasinghe, U. Sonnadara, M. Berg, and V. Cooray, J. Electrostatics, 65 8 (2007) 521-526
The lightning radiation field spectra of cloud flashes in the interval 20kHz to 20MHz
The lightning radiation field spectra of cloud flashes in the interval 20kHz to 20MHz, U. Sonnadara, V. Cooray, and M. Fernando, IEEE Transactions on Electromagnetic Compatibility, 48 1 (2006) 234-239
Characteristics of cloud to ground lightning flashes over Sweden
Characteristics of cloud to ground lightning flashes over Sweden, U. Sonnadara, V. Cooray and T. Gotschl, Physica Scripta, 74 (2006) 1-8
Trends of rainfall in Sri Lanka over the last century
Utilizing over 100 years of rainfall records in 15 meteorology stations, an analysis was carried out to extract the trends of annual rainfall depth in Sri Lanka over the last century. A statistically significant increasing trend of rate 3.15 mm/year was observed at Colombo and decreasing trends were observed at Nuwara Eliya and Kandy with rates of 4.87 mm/year and 2.88 mm/year respectively. Since no coherent increase or decrease of rainfall in any group of stations in the wet or dry zones was observed, the possibility of large scale change over the past century was ruled out. However, more recent data records (1949 onwards), revealed a decreasing trends in 13 of the 15 stations. Thus, traces of a temporal change seem to be apparent in the rainfall records over the last half century. In general, the downward trends in recent decades are steeper than the long term variations. For the recent data records, the largest downward trend of 11.16 mm/year was observed at Batticaloa.
Spatial interpolation of weekly rainfall depth in the Dry zone of Sri Lanka
Daily rainfall data recorded at 13 stations were analyzed to study the spatial patterns of rainfall in the dry zone of Sri Lanka. Principal component analysis was utilized to classify the dominant spatial regions. The first 2 eigenvectors accounted for 70.2% (the first eigenvector 54.8% and the second 15.4%) of the total variation, which clearly supports the commonly used major climatic division of Sri Lanka into wet and dry zones. Both the inverse distance weighting method and kriging successfully estimated weekly average rainfall in the North Central dry zone of Sri Lanka. For both methods, high correlation coefficients of 0.88 and 0.91 were observed for the southwest and northeast monsoon periods, respectively, with slightly lower values for intermonsoon periods. For inter-monsoon periods, the inverse distance weighting method produced better results than kriging. This work shows that the strength of the predictions depends on the rainfall seasons as well as the geometrical placement of the stations in the dry zone.