RSPAbstsJune
advertisement
Indian Journal of Radio & Space Physics VOLUME 29 NUMBER 3 JUNE 2000 CONTENTS Radiometric measurements of rain attenuation and estimation of rain height P K Karmakar, S Chattopadhyay, A K Sen & C J Gibbins A statistical comparison of Indian MST radar and rawinsonde wind measurements P Kishore, K Krishna Reddy, D Narayana Rao, P B Rao, A R Jain, G V Rama & S Sankar Meteorological and anthropogenic influences on the atmospheric aerosol characteristics over a tropical station Mysore (12N) N V Raju, B S N Prasad, B Narasimhamurthy & M Thukarama Seasonal variation of ambient air quality at selected sites in Agra city Richa Mudgal, Bhaskar Sharma, Rajeev Upadhyay & Ajay Taneja Experimental study on deposition of oxides of sulphur and nitrogen on dry and wet surrogate surfaces R S Parmar, G S Satsangi, Anita Lakhani, S S Srivastava & Satya Prakash Study of emissivity of dry and wet loamy sand soil at microwave frequencies O P N Calla & B Deka 95 102 115 127 134 140 NOTES On the nighttime enhancement of NmF2 at Jicamarca on 4-5 September 1964 Arjun Tan Indian Journal of Radio & Space Physics Vol. 29, June 2000, pp. 95-101 146 Radiometric measurements of rain attenuation and estimation of rain height P K Karmakar, S Chattopadhyay & A K Sen Institute of Radiophysics and Electronics, University of Calcutta, 92, Acharya Prafulla Chandra Road, Calcutta 700 009 and C J Gibbins Radio Communications Research Unit, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11OQX, UK Received 15 September 1999; revised 24 January 2000; accepted 26 February 2000 Measurements of rain attenuation at 22.235 and 31.4 GHz have been made during 1991 in Calcutta using microwave radiometers, and compared with calculated attenuation using different rain drop-size distributions. For low rain rates, the Joss et al.’s (drizzle) distribution was found to be the most appropriate. From the radiometric measurements and calculated attenuations, estimates have been made of the rain height and compared with predictions made from the ITU-R model. For the year 1991, the rain height was estimated to be 2.7 km at 22.235 GHz and 2.3 km at 31.4 GHz, as compared to a value of 3.1 km predicted by the ITU-R model. Indian Journal of Radio & Space Physics Vol. 29, June 2000, pp. 102-114 A statistical comparison of Indian MST radar and rawinsonde wind measurements P Kishore*, K Krishna Reddy & D Narayana Rao Department of Physics, Sri Venkateswara University, Tirupati 517 502 and P B Rao & A R Jain National MST Radar Facility, P.O.Box No.123, Tirupati 517 502 and G V Rama & S Sankar SHAR Centre, Sriharikota 524 124 Received 5 June 1999; revised 18 January 2000; accepted 8 February 2000 Comparisons are made between horizontal wind measurements carried out using Indian MST radar at Gadanki (13.47N, 79.18E) and rawinsonde launched from SHAR centre, Sriharikota (13.7N, 80.2E). The spatial separation of MST radar and rawinsonde is about 90 km. The MST radar horizontal wind velocities are derived from Doppler wind measurements at zenith angle of 20 in two orthogonal planes. For the first time, using Indian MST radar in the tropics, extensive intercomparison results are presented up to an altitude of 18 km. Measurements over a period of 4 months (June – September 1993) are considered, but the major part of the study involves a statistical analysis of data. The intercomparison was carried out using two methods. First, the comparison was made using the entire data obtained from both the instruments. Secondly, the comparison was repeated with data excluded whenever the instruments have large disagreements in excess of 15 m/s. Comparison of hourly-averaged radar and rawinsonde wind measurements shows fairly good agreement between them. However, the present study reveals that radar-derived horizontal winds are underestimated when compared with rawinsonde values over the height range 3.6-18 km. The aspect sensitivity of radar echoes may cause for underestimation of horizontal wind. Comparison of horizontal wind measurements from the MST radar and the rawinsonde differs with a standard deviation of 2-2.5 m/s. Differences between the radar and balloon wind measurements can be attributed to a combination of three factors: (i) wind variability over the spatial separation between the two sites, (ii) temporal variability and (iii) errors in the wind measurements. The present comparisons successfully demonstrate that both radar and rawinsonde give consistent wind measurements. Indian Journal of Radio & Space Physics Vol. 29, June 2000, pp. 115-126 Meteorological and anthropogenic influences on the atmospheric aerosol characteristics over a tropical station Mysore (12N) N V Raju, B S N Prasad, B Narasimhamurthy & M Thukarama Department of Physics, University of Mysore, Mysore 570 006 Received 28 April 1999; revised 29 November 1999; accepted 3 January 2000 The aerosol spectral optical depths (p) at narrow wavelength bands in the visible and near infrared range are obtained using a ground based multi-wavelength radiometer at the tropical continental station Mysore (12N, 76E). These data for a ten-year period (1988-1998) are examined for average temporal and spectral characteristics. The temporal variations reveal a summer high and winter low in p which get influenced largely by meteorological factors.The spectral features suggest impact of prevailing meteorological processes and probable anthropogenic influence. Indian Journal of Radio & Space Physics Vol. 29, June 2000, pp. 127-133 Seasonal variation of ambient air quality at selected sites in Agra city Richa Mudgal1, Bhaskar Sharma1, Rajeev Upadhyay2 & Ajay Taneja1 1Department 2U of Chemistry, St. John’s College, Agra 282 002 P Pollution Control Board, Agra 282 007 Received 20 October 1999; revised received 20 January 2000 The seasonal variation in the ambient air concentration of SO2, NO2 and suspended particulate matter (SPM) in the urban atmosphere of Agra, India, during the year 1998-99, has been reported. The city was hypothetically divided into six monitoring zones. The maximum concentrations of SO2, NO2 and SPM were observed at Foundry Nagar and St. John’s crossing. However, the minimum concentrations of SO2 and NO2 were observed at Dayalbagh, while the SPM concentration were minimum at Tajganj region. The value of SPM was always found higher than the prescribed limit of 100 µgm3, while the values of SO2 and NO2 were found within the permissible limits, except sometimes in winter seasons, which may be due to thermal inversion. The value of monthly average pollutant standard index (PSI) has also been reported. The value varies from 127 to 497 in Agra. Indian Journal of Radio & Space Physics Vol. 29, June 2000, pp. 134-139 INDIAN J CHEM., SEC. A, JUNE 2000 4 Experimental study on deposition of oxides of sulphur and nitrogen on dry and wet surrogate surfaces R S Parmar, G S Satsangi, Anita Lakhani, S S Srivastava & Satya Prakash Department of Chemistry, Dayalbagh Educational Institute, Dayalbagh, Agra 282 005 Received 20 May 1999; revised 26 November 1999; accepted 17 January 2000 Dry deposition of oxides of S and N, which contributes significantly (30-50 %) to the total deposition of SO42 and NO3 in temperate countries has been determined over surrogate surfaces. Wet and dry surrogate surfaces were exposed to collect SO2, NOx, SO42 and NO3. The trace gases SO2, NOx, HNO3 and particulate SO42 and NO3 were measured simultaneously to determine deposition velocities. Deposition fluxes (µg m2 d1) of SO2, NOx, SO42, NO3 were found to be 250.6 13.0, 319.7 27.6, 8640 36.2 and 6048 51.8 on the wet surfaces and 44.9 12.9, 12.0 4.8, 777.6 35.4 and 864 45.7 on the dry surfaces, respectively. The mean vapour phase concentrations (µg m3) of SO2, NOx, HNO3 and particulate SO42 and NO3 were 8.7, 24.4, 2.7, 14.6 and 3.0, respectively. From these measured values, deposition velocities of SO2, NOx, SO42 and NO3 were calculated for the wet and dry surfaces. The velocities were found to be higher on the wet surfaces. An attempt has also been made to differentiate between the contributions of different phases to the total dry deposition of SO42 and NO3. Indian Journal of Radio & Space Physics Vol. 29, June 2000, pp. 140-145 Study of emissivity of dry and wet loamy sand soil at microwave frequencies O P N Calla International Centre for Radio Science, “OM NIWAS” A-23, Shastri Nagar, Jodhpur 342 003 and B Deka Department of Electronics and Telecommunication, Assam Engineering Institute, Guwahati 781 003 Received 8 November 1999; revised 7 February 2000; accepted 1March 2000 Results of estimation of emissivity from dielectric constant of dry and wet soil using emissivity model for microwave frequencies ranging from 2 GHz to 20 GHz are presented. The measurements of the dielectric constant of dry and wet soil had been carried out using HP network analyzer and HP dielectric probe employing co-axial probe method. The estimations are made with incidence angles 0, 30, 45 and 60 for both horizontal and vertical polarization. The emissivity, which is less than one, increases with frequency and decreases with moisture content. In both the cases emissivity for vertical polarization is higher than that for horizontal polarization. NOTES Indian Journal of Radio & Space Physics Vol. 29, June 2000, pp. 146-148 On the nighttime enhancement of NmF2 at Jicamarca on 4-5 September 1964 Arjun Tan Department of Physics, Alabama A & M University, Normal, AL 35762, U S A Received 20 December 1999; revised received 27 March 2000 The peak electron density of the ionosphere (NmF2) near the dip equator often exhibits a characteristic enhancement after midnight hours. The principal agent which causes this enhancement is a downward drift of sufficient magnitude when the compression of the plasma overcomes the chemical loss rate. This has been verified in a few cases where the velocity of the drift could be determined from successive profile measurements. When the intermediate profiles are unavailable, different plausible drift velocity models which produce the same total downward descent may be considered. Two distinct drift velocity patterns after midnight hours including a constant velocity drift pattern and an accelerated drift velocity pattern are recognised from drift measurements over Jicamarca. It is shown that the accelerated drift velocity model is more effective in producing the nighttime enhancement than the constant velocity drift model. This analysis, when applied to the nighttime enhancement of NmF2 at Jicamarca on 4-5 September 1964, shows that an accelerated drift was necessary to produce that particular enhancement.
