DUST STORM-A CASE STUDY OVER PATNA AND NEIGHBOURED

Transcription

1 DUST STORM-A CASE STUDY OVER PATNA AND NEIGHBOURED * R. K. Giri 1, D. Pradhan 2 and A. K. Sen 1 1 Meteorological Centre, Patna, Bihar, India 2 Regional Meteorological Centre, Kolkata, India *Author for Correspondence ABSTRACT During Pre-monsoon season (March-May) duststorm /thunderstorm activities are common over Bihar region. Their prediction sometimes becomes very difficult due to instant build up of localized convection. Their timely prediction synoptically or through satellite observations is difficult. In that case timely warning cannot be issued by aviation and weather agencies. Such a mesoscale system (duststorm) was formed on 04 April, 2013 about 200 Km West- North-West of Patna (India). Dusts raising winds of wind sapped around 40 km /hr reduced the visibility appreciably (< 50 meter) and affect the traffic (air and land). According to news agencies duststorm engulfs the city for few hours and no major loss was reported. Doppler weather radar (DWR) at Patna observed the system as the signature, ripples like patters in the maximum radar reflectivity from West- North -West direction. On the other hand, duststorm accompanying with rain or thunderstorm events scattering signatures are quite different than purely duststorms and in the most cases of thunderstorms radar reflectivity are higher than dust. Present study establishes that DWR is very useful for prediction of such mesoscale systems along with its direction of movement. To highlight the contrasting features of DWR reflectivity and enhance nowcasting potential one thunderstorm (27 April, 2013) is also studied. The study also revealed that an early warning of strong winds for aircrafts and public could have been issued for development of such short duration disastrous weather event using DWR data well in advance. Kew Words: Doppler Weather Radar, Duststorm/Thunderstorm and Wind Speed INTRODUCTION It is very difficult to forecast the short lived mesoscale weather phenomena (duststorm/thunderstorm) precisely. These weather systems affect the Bihar region with different frequency and capacity throughout the year. The impact or intensity of these events depends on the horizontal and vertical spread of the system. The occurrence of these natural extreme events is modified by the induced or aggravated by humans up to a certain extent. Sometimes very high wind speed of gusty winds or sudden heavy downpour disrupt or damages the valuable goods, buildings, communication system, ecology of natural environment etc. The impact after the event depends on the awareness about the weather forecast or warnings during bad weather and proper planning of safety and rescue. The vulnerability increases if the habitat is densely populated and sustained with poor urban planning and unorganised manner. After the winter, pre-monsoon season begins and large land mass is heated by solar heating. This makes the air near the ground warm which lifts vertically and gets cooled after adiabatic expansion. If the air is dry then its temperature decreases with faster rate. On the other hand if the environmental air moist then after it gets saturation, condensation begins which releases the latent heat. Due to this latent heat of condensation the moist air temperature changes becomes slow as it go up as compared to the dry air. During this time if the surrounding environment temperature change with height is more as compare to the moist air under consideration, then the flow will remain laminar. It will be turbulent and generate instability in the atmosphere. Instability induced by convection also known as convective instability. Duststorm /thunderstorms are associated with local instability have more vertical growth as large cumulus or cumulonimbus type of clouds. These systems are normally associated with squally winds of short duration ranging from few minutes to hours. The system has strong updrafts and downdrafts and turbulence is also very high. If the air is dry then strong turbulence will results strong downdrafts with the passage of squalls and dust raised up to considerable height. These dust raising winds reduces the visibility to a very low value. This disrupts the normal life as well air and land traffic appreciably. These events are more frequent over Bihar region and approaches over the area in North-west directions and popularly known as Nor westers or Kal Baishakhi. At times, the visibility reduces nearly zero and night like conditions appears during day time. Hence, duststorms are called Andhi in India. Joseph et al., (1980) classified the Andhi into four types and this convective type of events can be as large as 30 kilometers. Joseph (1982) proposed the downdraft model for Andhi which assumes that the Andhi head moves forward more slowly at night, when the ambient air density is higher and visibility improvement is slower as compared to type 1 st of duststorms. The criteria of moderate duststorm based on wind and horizontal 51

2 surface visibility is wind speed between 39 to 74 kmph and horizontal visibility less than 1000m up to 500 m and for severe case wind speed 75 kmph and horizontal visibility less than 500m up to 50 m (Giri et al., 2012). Typical sizes of dust storm particles are in the range of microns to about one tenth of a millimeter: According to figures in Niu et al., (1999), more than 90 percent of dust storm particles have sizes between 0.5 and 3.0 microns.in contrast to such extremely small particles, Goldhirsch (1982) reports that about 45 percent of dust storm particles have sizes of more than 10 microns. Fedorov and Stepanenko (1978) found that particles of 30 to 60 micron size are displaced by several hundred kilometers during dust storms. Generally, in most of the cases dust raising winds are accompanied with rain. Keeping this point into consideration last 15 years ( ) thunderstorm data is analysed month-wise. In recent past, Pradhan et al., (2012), Pradhan and De (2012) Suresh et al., (2005) studied short lived weather phenomena with the help of Doppler weather radar (DWR) data and computed convective indices for several cases of thunderstorms events. MATERIALS AND METHODS The DWR and realised thunder storms data over Bihar region along with high speed wind system data for Patna is taken from meteorological centre, Patna. Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model data is taken from global web site ( and utilized for tracing the probable origin of the duststorm event. RESULTS AND DISCUSSION Distribution of Duststorm/thunderstorm over Bihar The climatological record ( ) of duststorm /thunderstorm over Patna and neighboured published by India meteorological department (IMD) are given in Table 1. These mesoscale systems affected Bihar region throughout the year in different proportions. Patna and Gaya stations are generally affected more by dust raising winds in comparison to Bhagalpur and Purnia area (Table 1). Table 2, shows the last 15 years ( ) month-wise thunder activity over Bihar region. The distribution of month-wise thunderstorm activities are shown in figures 1 to 4. Table 1: Annual mean of Climatological frequencies (No. of days) of Duststorms/ Squall (DS/SQ) Station Annual mean (DS/SQ) Lucknow 7.5/1.2 Allahabad 8.4/0.0 Kanpur 8.1/0.0 Varanasi 3.7/0.0 Patna 4.2/1.2 Gorakhpur 4.1/0.0 Chapra 0.5/0.0 Gaya 1.4/3.3 Bhagalpur 3.1/0.7 Purnia 1.1/0.0 (* Source: I.M.D. Climatological Tables, ) Figure 1: Thunder-events (month-wise) over Patna during last 15 years ( ) 52

3 Table 2: Frequency (No. Of days Month-wise) of thunder-events over Bihar region last 15 years ( ) YEAR STATION JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 2000 PTN GYA BGP PRN PTN GYA BGP PRN PTN GYA BGP PRN PTN GYA BGP PRN PTN GYA BGP PRN PTN GYA BGP PRN PTN GYA BGP PRN PTN GYA BGP PRN PTN GYA BGP PRN PTN GYA BGP PRN PTN GYA BGP PRN PTN GYA BGP PRN PTN GYA BGP PRN PTN GYA BGP PRN PTN GYA BGP PRN

4 Figure 2: Thunder-events (month-wise) over Gaya during last 15 years ( ) Figure 3: Thunder-events (month-wise) over Bhagalpur during last 15 years ( ) Figure 4: Thunder-events (month-wise) over Purnia during last 15 years ( ) 54

5 It is well known that pre monsoon season (March-May) is more susceptible for duststorms as compared to monsoon and other seasons. In other seasons (Monsoon, post-monsoon and winter), thunder activities are more common as compared to duststorms. It has been observed that maximum thunderstorm activities in monsoon (June to September) season followed by post-monsoon, pre-monsoon and winter. These events are easily captured by the latest state of art DWR system installed at Patna and informed to the affected public well in advance (2 to 3 hour). Maximum reflectivity of Doppler weather Radar On April 4, 2013 afternoon Patna city engulfed with a duststorm which disrupt badly the normal city life and aviation activities at Jai Prakash Narayan Airport (JPNI) y reducing the visibility < 50 meter. The event is captured well in advance by DWR Patna (Figs. 7, 8 & 9) and warnings are issued accordingly. The wind speed reached up to 40 km /hour as recorded by the high wind speed recording system (HWRS) installed at meteorological centre JPNI airport, Patna, figure (5). Figure 5: Wind speed and direction of dust storm (1400 hrs IST to 2000 hrs IST) on 04 April 2013 over Patna (Bihar) In almost similar fashion another event on 27 April, 2013 which affected the city and neighbouring area. This event is also captured well in advance by DWR Patna. The DWR reflectivity of 27 April, 2013 thunder activity is shown in figures 10, 11 &12. The wind speed and direction recorded by HWRS is shown in figure 6. The wind speed and direction recorded at Patna is about 40 km /hour and north-west respectively. The difference of DWR reflectivity in 2 both cases may be due to that backscattering constant K of dust particles is different from that of water droplets. The 2 K values of the dust particles are about 0.3 which is factor of three less than 2 K of water droplets, Goldhirsch (1982). The dust particles sizes are very small as compared to the precipitation. Due to this reason the reflectivity values of duststorm in C-band Radar are very low as compared to thunderstorm. The variations in the reflectivity in case of dust are very small and smooth, while in thunderstorms have large variations in reflectivity. The dust particles are lifted by wind and winds are higher than laminar flow and hence flow becomes turbulent. As a consequence the turbulence is measured more directly than mean wind speed. The vertical lifting of the dust particles depends on the size of the particles. If the sizes are large than these particles will be less lifted. Hence, duststorm exhibit a negative vertical reflectivity gradient in contrast of thunderstorm event. This study is important because this type of event is first time captured over Bihar region after the successful working of Doppler weather 55

6 radar on 27 th Decemer, Timely warnings were issued in advance for aviation as well as general public and state government officials. HYSPLIT trajectory analysis The weather event (duststorm/thunderstorm) is captured well in advance if the system is within the range of DWR. Beyond 250 km of range the accuracy will be less and uncertainty increases. To know the probable origin of the event beyond the range of DWR Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) analysis is very important. Figure 6: Wind speed and direction of thunderstorm (1400 hrs IST to 2000 hrs IST) on 27 April 2013 over Patna (Bihar) Figure 7: Maximum DWR reflectivity duststorm (04 April 2013: 11:31 IST) 56

7 Figure 8: Maximum DWR reflectivity duststorm (04 April 2013: 12:51 IST) Figure 9: Maximum DWR reflectivity duststorm (04 April 2013: 13:51 IST) 57

8 Figure 10: Maximum DWR reflectivity thunderstorm (27 April 2013: 11:31 IST) Figure 11: Maximum DWR reflectivity thunderstorm (27 April 2013: 12:51 IST) 58

9 Figure 12: Maximum DWR reflectivity thunderstorm (27 April 2013: 13:51 IST) Figure 13: HYSPLIT backward trajectory analysis on 04 April

10 HYSPLIT single-particle backward-trajectory analysis using inputs from Global Data Assimilation System (GDAS) at different receptor heights. In the case of 4 th April, 2013 duststorm event we have selected the receptor source heights at 500, 100, 1500 and 2000 m. The model is developed by Air Resource Laboratory (ARL) and internet based model can run in a personal computer. The web output is generated by Real time Environmental Applications Display system (READY). The output for 4 th April, 2013 case is shown in figure 13. It has been observed from figure 13, that the origin the duststom on 4 th April 2013 is more localized then distant. The sky was clear after few hours of the event in Patna. This may be because of short resident time of suspended particles present in the atmosphere. The working of the source models begin with emission rates and estimate ambient concentrations at receptors after considering transport, dispersion, deposition, and chemical transformation processes (Zannetti, 2005). The analysis is very useful in forecasting to predict the durability or persistence of the such type of weather system. CONCLUSION The short lived phenomena (duststorm /thunderstorm) affected badly the rail,air and land traffics. If the wind speed or associated rains are strong then its effects on crops, lives of the people are more prominent as compared to the normal weather activities. To minimize the losses it is need for forecasting precisely the events well in advance by analyzing speed and movement of the system. The following main points are brought out from the study: The DWR reflectivity signature of duststorm events are smooth and lesser height in vertical as compared to the thunder events. Dust raising winds reflectivity variations are small and exhibit a negative gradient in vertical reflectivity. DWR can provide the warning 2 to 3 hours in advance to the public depending on the speed of the movement of the weather system. By doing HYSPLIT trajectory analysis origin of transport of the suspended particles can be estimated. Precise weather warning may be issued well in advance to aviation, agriculture and general public. ACKNOWLEDGEMENT The author is grateful to the Director General of IMD for providing the data of this study. Supporting help of the ARL team in generating the HYSPLIT trajectory data is duly acknowledged. REFERENCES Federov AA & Stepanenko VD (1978). Radar identification of dust storms. T. Vyp.411, Glav. Geof. Obs., Leningrad, Giri RK, Rani P, Prakash S & Singh J (2012). Satellite viewed duststorms: An overview. International Journal of Physics and Mathematical Sciences, 2(1) Goldhirsch J (1982). A parameter review and assessment of attenuation and backscatter properties associated with dust storms over desert regions in the frequency range of 1 to 10 GHz. IEEE Transactions on Antennas and Propagation, AP-30(6) Joseph PV (1982). Atentative model of Andhi. Mausam, 33(4) Joseph PV, DK Raipal & Deka SN (1980). Andhi, the convective duststorm of northwest India. Mausam, 31(3) Niu S, Sun J, Yu Y, Sang J, Zhai T, Thang C, Chen Y, Ji R & Huang S (1999). Statistical analysis and observational study of sandstorm in Mt. Helanshan area. First LAS WMO International Symposium on sand and dust storms, Damascus, Pradhan D, De UK & Singh UV (2012). Development of nowcasting technique and evaluation of convective indices for thunderstorm prediction in Gangetic West Bengal (India) using Doppler Weather Radar and upper air data. Mausam, 63(2) Pradhan D & De UK (2012). Doppler Weather Radar analysis of short term cyclonic storm. Mausam, 63(3) Suresh R, Arvindan V, Rajesh P, Rao R & Bhatnagar AK (2005). Clear air echoes from the atmospheric boundary layer over Chennai-A study using S-band Doppler Weather Radar. Mausam, 56(2) Zannetti P (2005). Air Quality Modeling: Theories, Methodologies, Computational Techniques, and Available Databases and Software-Volume II. Advanced Topics; A&WMA: Pittsburgh, PA. 60