MAUSAM, 56, 2 (April  2005), 337-342

551.511 : 551.553.21         

 

Contrasting features of wave number one during northern summer

monsoon seasons of 1997 and 2002

 

S. M. BAWISKAR, M. D. CHIPADE, V. R. MUJUMDAR, U. V. BHIDE and  S. S. SINGH

Indian Institute of Tropical Meteorology, Pune - 411 008, India

 (Received 30 December 2003)

 

ABSTRACT. Temporal and spatial variations of the energetics of the lower tropospheric zonal wave number one are compared for monsoon 2002 (a recent drought year) and monsoon 1997 (a normal monsoon year).  Fourier technique is used to calculate momentum transport, kinetic energy and wave to wave interaction. Daily global grid point NCEP wind (u & v) data at 850 hPa for 153 days (1 May to 30 September) are considered.

 

                Daily and weekly variations of the energetics of wave number one indicate that as long as the momentum transport or kinetic energy of wave number one around 10° N  is strong, the rainfall is better and vice-versa. The  amplitude of wave number one was almost half during 2002 as compared to that of during 1997,  which resulted into less transport of momentum and meager supply of kinetic energy throughout the monsoon season of 2002. The significant release of kinetic energy by wave number one may have played a vital role in triggering five intense systems during 1997 whereas the  weak supply of kinetic energy  may have failed to trigger a single system during monsoon 2002.

 

Key words  -  Temporal and spatial variations, Fourier technique, Momentum transport, Kinetic energy.               

 

 

 

 

 

MAUSAM, 56, 2 (April  2005), 343-356

551.509.313(540)

 

Improvements in the weather prediction over the Indian region

using regional spectral model

 

Y. V. RAMA RAO, S. C. KAR*, T. S. V. VIJAYA KUMAR**,  S. R. KALSI,  H. R. HATWAR

and

S. K. ROY BHOWMIK

India Meteorological Department, New Delhi – 110 003, India

*National Centre for Medium Range Weather Forecasting (NCMRWF), NOIDA, U.P., India

**Department of Meteorology, Florida State University, Tallahassee, USA

(Received 6 May 2003, Modified 13 May 2004)

 

ABSTRACT. Florida State University Regional Spectral Model (FSURSM) has been installed at India Meteorological Department, New Delhi and test runs have been made. A suitable change in the model code were made to use analysis and forecast fields as initial and boundary conditions for the model from the global T-80 model run at the National Centre for Medium Range Weather Forecasting (NCMRWF). The resolution of the regional spectral model is 0.75° transform grid, which is equivalent to the resolution of a T-170 global model. The model has been integrated for 3 days and studies undertaken to test the performance of the regional model in respect of some of the major weather events that occurred during December 2002 and February 2003. Using initial analyses from ECMWF and NCMRWF, the impact of initial fields on model forecast is also investigated. The case studies show that the forecasts from the regional spectral model are reasonably close to the observed features. The intensity and movement of model simulated systems are in good agreement with the observations.

 

Key words  -             Spectral model, Western disturbance, Easterly wave, Forecast.

 

MAUSAM, 56, 2 (April  2005), 357-366

551.509.313 : 551.501.7

 

Operational use of improved profiles by using neural network technique derived from NOAA satellites microwave data in NWP model over Indian region

 

DEVENDRA SINGH, Y. V. RAMA RAO, R. C. BHATIA, S. K. SRIVASTAV, SANT PRASAD

and

S. K. MUKHARJEE

India Meteorological Department, New Delhi – 110 003, India

(Received 4 February 2004, Modified 20 May 2004)

 

ABSTRACT. India Meteorological Department, New Delhi receives and process NOAA TOVS and ATOVS data in real time. The physical and neural network approaches have been used to retrieve atmospheric temperature and moisture profiles from NOAA-16 & 17 satellites AMSU data over Indian region. The earlier training data set based on global data only for two seasons used in neural network technique has been replaced by new training data set based on regional data over land and ocean for all the seasons. The new training data set has improved the temperature and moisture profiles accuracy retrieved using neural network approach compared to physical method. The detail validation and inter comparisons of temperature and moisture profiles have also been carried out with ECMWF analysis over sea and land separately for different seasons for the year 2002-2003. The performance of neural network technique is found to be superior compared to physical method.

 

Recently, temperature and moisture profiles retrieved from NOAA-16 ATOVS data over Indian region have been used in regional NWP model for the impact study. The operational NWP system of India Meteorological Department is based on a Limited Area Analysis and Forecasting System (LAFS), which consists of real time processing of data received on Global Telecommunication System (GTS), objective analysis by 3-D multivariate optimum interpolation (OI) scheme and a multi-layer primitive equation model. Several experiments were performed using temperature and moisture profiles retrieved from NOAA-16 ATOVS data. Using this data several experiments were undertaken to examine the impact of these data sets on some of the important weather systems such as monsoon depression, active monsoon conditions during monsoon 2003. The preliminary studies reveal that these additional data have a positive impact on rainfall prediction of the limited area model. Results of specific cases of impact studies are presented in the paper.

 

Key words – Neural network, AMSU, Model Impact, NOAA, GTS.

 

 

MAUSAM, 56, 2 (April  2005), 367-374

551.579.4 : 551.588.16 : 556.53  

 

Spectral characteristics and ENSO relationship of the Paraná river streamflow

 

R. P. KANE

Instituto Nacional de Pesquisas Espacias – INPE

C. P. 515, 12245-970 – São José dos Campos, SP, Brazil

 (Received 27 November 2003,   Modified 20 April 2004)

 

ABSTRACT. A spectral analysis of the Paraná river stream flow for 1904-1999 for 3 seasons indicated a periodicity of ~8.5 years in all seasons, with extra periodicities at ~17, ~5, ~3.7 and ~2.8 (QBO) years in JFMA months, at ~29, ~13, ~4.7, ~3.7, ~2.4 and ~2.1(QBO) years in MAMJ months, and at ~27 and ~3.4 years (no QBO) in SOND months. El Niños were associated with positive anomalies (floods) of the stream flow, with lags of few months. Pacific SST anomalies were of the same peak magnitude in the giant El Niño events of 1982 and 1997, but the stream flow anomalies were much larger in 1983 as compared to 1997. The rise and fall of the stream flow anomalies was oscillatory with peak separation of ~5 months.

 

Key words  -  QBO, El Niño, SST anomalies

 

 

 

 

MAUSAM, 56, 2 (April  2005), 375-384

551.555.6 : 551.515.7(9)         

 

 

The effect of atmospheric blocking high and ridges on weather

over Maitri, East Antarctica – A case study

 

E. KULANDAIVELU, S. SRIDHARAN and S. R. RAMANAN

Regional Meteorological Centre, Chennai – 600 006, India

(Received 11 March 2003, Modified 18 August 2004)

 

 

ABSTRACT. The Indian Antarctic station, Maitri is often experiencing continuous blizzard over a week with strong surface winds and surface temperature anomalies due to atmospheric blocking during winter and spring seasons of Antarctica. One such case during the last week of August 2000 and another case in mid-July 1996 are studied. There is more blocking activity in winter and spring months. The influence of blocking high on weather parameters during the study period is also presented.

 

Key words − Blizzard, Blocking, Geopotential height, Ridge and advection.

 

 

 

 

 

 

 

MAUSAM, 56, 2 (April  2005), 385-394

551.524.36(548.23)

 

Heat waves over Andhra Pradesh : A case study of  summer 2003

 

C. V. V. BHADRAM,  B. V. S. AMATYA, G. B. PANT*,

and

K. KRISHNA KUMAR*

Meteorological Centre, Airport, Hyderabad, India

*Indian Institute of Tropical Meteorology,  Pune - 411 005 India

 (Received 6 January 2004, Modified 24 June 2004)

 

 

ABSTRACT. Temperature data of pre-monsoon months for major stations in Andhra Pradesh for long period (1901-2002) have been analysed to identify the variations in maximum temperature. Analysis of short period temperature data (1986-2002) has shown increase in the frequency of severe heat waves and also duration of heat wave spells during the last decade. Since the severe heat waves during May-June 2003 over Andhra Pradesh have claimed many lives, a detailed study of all meteorological parameters associated with such heat waves has been made and the results are discussed. Human comfort indices - Heat Index (HI),  Thom’s Discomfort Index &  Webbs’  Comfort Index  computed in respect of coastal stations have clearly reflected the severity of heat waves.

 

Key words – Heat wave, Maximum temperature, Frequency, Human comfort index.

 

 

 

 

MAUSAM, 56, 2 (April  2005), 395-400

551.515.13         

 

Decaying characteristics  of  severe cyclonic storms after landfall

over east coast of India

 

 

CHARAN SINGH and B. K. BANDYOPADHYAY

India Meteorological Department, New Delhi – 110 003, India

(Received 31 March 2004, Modified 12 October 2004)

 

 

ABSTRACT. Severe tropical cyclones are responsible for large casualties and considerable damage to property and agricultural crop. After the landfall, the main damages from cyclones are due to strong wind. An attempt has been made in this paper to study the nature of decay of wind speed of tropical cyclones after landfall for the period 1990-2003. It is found that the maximum wind speed decreased exponentially after landfall. A severe cyclonic storm decay to cyclonic storm within 6 to 9 hours after landfall where as very severe cyclonic storm decay to severe cyclonic storm within 6 hours and to cyclonic storm within 15 hours after the landfall. The mean decay rate is found to be  0.46 for the  first 6 hours and 0.59 for the subsequent 6 hours.

 

Key words – Decay curve, Decay rate, Reduction factor.

 

 

 

 

 

 

 

MAUSAM, 56, 2 (April  2005), 401-404

551.501.75    

 

Representative scales of LASPEX wind data

 

SUBROTO SINHA

Indian Institute of Tropical Meteorology, Pune – 411 008, India

(Received 9 April 2003, Modified 15 July 2004)

 

 

ABSTRACT. In this study, an attempt is made to identify the appropriate scales for the wind data over the stations covered in the LASPEX experiment, which can be considered to represent the large-scale wind pattern, representative of the whole area, covered by the field experiment. The divergence field was chosen for this purpose. The mean of the latitudes and longitudes of all the five stations was calculated and this represented the latitude and longitude respectively, of the central point. The wind components at each of the five stations were arbitrarily represented by a trigonometric function of wavelength and distance from the central point, which was considered as the origin. The divergence values at each station were computed and the mean value over all the stations was found. The same values of winds were used to compute the large scale divergence field over the area, by applying the method devised by Yanai et al. (1973). It was seen that for wavelengths greater than 2830 km, the ratio of the two divergences was greater than 0.9, suggesting that this was the limiting value of the wavelength which can be considered as representative of the entire area.

 

Key words – Representative scales, Limiting wavelength, LASPEX

 

 

 

 

 

 

MAUSAM, 56, 2 (April  2005), 405-416

551.509.59 : 551.586.633.18         

 

Weather based forewarning of green jassid attack on kharif rice and     operational crop protection at Pattambi, Kerala

 

R. P. SAMUI,  N. CHATTOPADHYAY,  J. P. SABLE,  K. KARTHIKEYAN*  and  P. V. BALACHANDRAN*

India Meteorological Department, Pune - 411 005, India

* Kerala Agricultural University, Pattambi - 679306, India

(Received 4 November 2003)

 

 

ABSTRACT. The feasibility of meteorological forewarning of green jassid attack has been made using entomological and meteorological data for a period of 15 years from 1987- 2001 recorded daily at Pattambi in Kerala. Stepwise multiple regression technique is used in this study for developing forewarning models. The study revealed that maximum and minimum temperature, morning and afternoon relative humidity, bright sunshine hours and weekly totals of rainfall have profound effect on the development of green jassid at their successive generations on kharif rice crop. Weather based multiple regression models for the peak infestation period for each of the generations of the pest          were developed using data for the period 1987-99 and validated using observed meteorological as well as pest data for 2000-01. Based on the findings of this study pest weather calendar for green jassid of kharif rice was prepared. This calendar would be useful for early warning and operational rice crop protection from green jassid attack.

 

Key words − Green jassid, Weather based forewarning, Operational rice protection.

 

 

 

MAUSAM, 56, 2 (April  2005), 417-424

551.586 : 551.521 : 633         

 

 

Heat unit requirement, radiation, water use and photoperiod during the

growing season of toria (Brassica campestris variety toria)

 

S. SENGUPTA,  K. GHOSH  and  H. P. DAS

India Meteorological Department, Pune  -  411 005, India

 (Received 03 December  2002, Modified 13 February 2004)

 

 

ABSTRACT.  The agrometeorological data of toria (variety M-27) at Jorhat and Shayamakhunta for the period 1986-87 to 1992-93 were used for assessing phenological development in relation to heat unit, water use, photothermal  and heliothermal unit and photosynthetically active radiation (PAR) requirement at Shayamakhunta and Jorhat.  Photothermal, heliothermal unit,  water use and PAR were higher at Shayamakhunta than that of Jorhat. Heat use efficiency (HUE) and radiation use efficiency (RUE) also showed variations in time and space which were comparatively higher in early sown crops. A curvilinear relationship between duration (days) and heat units was derived seperately for sowing to flowering and pod formation to physiological maturity stages which showed consistent positive correlations at both locations.      

 

Key words  − Photothermal unit, Heliothermal unit, Photosynthetically active radiation, Heat use efficiency, Radiation use efficiency.         

     

 

 

 

 

MAUSAM, 56, 2 (April  2005), 425-432

551.509.59 : 551.586 : 633         

 

Forewarning of incidence of Tikka disease on groundnut and operational

crop protection using weather information in Gujarat

 

R. P. SAMUI, N. CHATTOPADHYAY and  P. S. RAVINDRA

Meteorological Office, Pune – 411 055, India,

 (Received 11 June 2002, Modified 12 April  2004)

 

ABSTRACT.  Studies were made to develop weather based forewarning models for the incidence of tikka disease on groundnut grown in Gujarat region. It was found that decrease in maximum and minimum temperature below 34° C and 22° C respectively and increase in morning and afternoon relative humidity above 82% and 78% respectively favoured the infestation of the disease. Synoptic weather conditions prior to the disease incidences showed that incursion of moist and cold air causing drop in maximum and minimum temperature and increase in morning and afternoon humidity were favourable for the disease infestation. This information would be useful for operational plant protection from the disease.

 

Key words − Tikka disease, Groundnut, Weather parameters, Forewarning models.

 

 

 

 

MAUSAM, 56, 2 (April  2005), 433-446

 

551.501.777 : 551.508.855(548.1)

 

On optimum rain rate estimation from a pulsed Doppler Weather Radar

at Chennai

 

R. SURESH,  P. K. RAVICHANDRAN,  J. P. GUPTA,  S. B. THAMPI,  S. KALYANASUNDARAM 

and

P. RAJESH RAO*

India Meteorological Department, Chennai - 600 001, India

*India Meteorological Department, New Delhi - 110 001, India

(Received 12 December 2002,  Modified 11 May 2004)

 

ABSTRACT. A 10 cm S-band Doppler Weather Radar (DWR) has been installed as a replacement of an outlived analogue S-band radar at Cyclone Detection Radar (CDR) station, Chennai during September-October, 2001. Technical specifications and capabilities of this DWR have been briefly mentioned in this paper. The digital data obtained from this DWR have been used for the period November-December, 2001 to estimate the rain rate based on the Marshall-Palmer relationship between the radar reflectivity factor (z) and the rain rate (R). The relation z = 267R1.345  estimates well the rain rate as measured by the self recording rain gauges located within 100 km radius from the DWR. This relationship has been tested for its operational applicability during March 2002 - December, 2003 and found that the accumulated precipitation from the radar estimation was within an error of 15% from the rain gauge measured values. Information on the twenty four hours accumulated areal distribution of precipitation can be used by the water managers and operational hydrologists  for the effective water management over the catchments since the error in rain rate estimation over a wider area is relatively small in comparison to point rainfall estimation. 

 

 

Key words  –           Rain rate, Doppler Weather Radar, Radar reflectivity factor, Drop size distribution, Marshall-Palmer relationship, Disdrometer.

 

 

 

 

 

 

MAUSAM, 56, 2 (April  2005), 447-464

551.510.522 : 551.508.855(548.1)

 

     

Clear air echoes from the atmospheric boundary layer over

Chennai – A study using S-band Doppler Weather Radar

 

R.  SURESH, V.  ARAVINDAN, P.  RAJESH RAO*  and  A.  K.  BHATNAGAR*

India Meteorological Department, Chennai - 600 001, India

*India Meteorological Department, New Delhi - 110 003, India

(Received 25 June 2003, Modified 19 February 2004)

 

ABSTRACT. During December 2002 – early April 2003, between 2345 and 0215 UTC and between 1230 and 1400 UTC covering the twilight period, radar reflectivities as high as 28-38 dBZ were measured in the atmospheric boundary layer by the Doppler Weather Radar (DWR) installed at Cyclone Detection Radar station, Chennai regularly. On analysis, it was found that these radar returns were not from precipitating clouds but from some other invisible source(s).  The contributory mechanisms for this high order of reflectivity have been analysed from meteorological and non-meteorological angles. Thermodynamical parameters and potential radio refractive index have been computed and analysed. The refractive index structure constant (Cn2) has been computed from the 0000 and 1200 UTC RS/RW data as well as from the radar reflectivity data. The prevalence of convectively unstable atmosphere in the first layer adjacent to the surface (upto 350 m a.g.l) at 1200 UTC and nocturnal surface inversion   at 0000 UTC contribute to the enhanced Cn2 in the range of 3.58 ´ 10-12  to 10-15 m-2/3 in the layers upto 900 m  a.g.l. This sort of Bragg scattering with high Cn2 could have contributed to radar reflectivity factor as high as +0.8 dBZ only. During the last three decades, there is an alarming increase in nocturnal surface inversion frequencies over Chennai presumably due to high concentration of suspended particulate matters and respirable dust particles. The contribution by these pollutants to the radar reflectivity factor is restricted to a maximum of about  – 0.9 dBZ only.  Migratory birds of about eight to twelve thousand in number  with 10 – 50 cm2 radar cross section  and possibly innumerable insects appear as sources of the enhanced reflectivity.

 

Key words  –           Doppler weather radar, Refractive index, Refractive turbulence structure constant () Birds, Insects, Radar ornithology, Inversion, Humidity, Boundary layer, Twilight.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MAUSAM, 56, 2 (April  2005), 465-472

550.34.044(540)   

     

Configuration of an optimum seismological network for India

S. K. SRIVASTAV, RAJESH PRAKASH, R. S. DATTATRAYAM, S. K. ARORA*, B. K. BANSAL**

and

S. N. BHATTACHARYA***

India Meteorological Department, Lodi Road, New Delhi, India,

*1, Shivam, Plot 121, Sector 28, Vashi, Navi Mumbai, India

**Department of Science & Technology, New Delhi, India

***Department of Geology & Geophysics, IIT, Kharagpur,  India

(Received 12 March 2004)

 

 

ABSTRACT.  India Meteorological Department (IMD) is the nodal agency of Government of India responsible for monitoring seismicity in and around the country. IMD maintains the national seismological network consisting of 47 permanent observatories, in addition to some observatories in northern India for special studies. A 16-element VSAT-based digital telemetry system for close monitoring of seismicity in and around Delhi is also in operation. In addition to IMD, several state/central government organizations, universities and R&D institutions are also operating seismological observatories in various parts of the country. Some of these observatories in the Peninsular shield region have been upgraded in the recent past with state-of-the-art digital broadband seismograph systems, in addition to opening 10 such new digital broadband stations. This paper makes an attempt to assess the magnitude threshold of routinely detecting and locating earthquakes occurring any where in the country with the existing IMD network. Using the seismic wave attenuation characteristics in the Himalayan and Peninsular shield regions, we have estimated epicentral distance up to which a regional earthquake of given magnitude can be detected and located as well. The minimum number of observatories required for uniform azimuthal coverage and accurate determination of hypocentral parameters has also been taken into consideration. An optimum seismological network configuration has been worked out based on the above inputs. It is found from the analysis that the existing IMD network is capable of detecting and locating earthquakes of magnitude 3.5 and above occurring in the mainland of the country, except for a few pockets in Rajasthan, Gujarat, Arunanchal Pradesh and J&K. An attempt has also been made to show that regional earthquake monitoring capability would largely improve by suitably upgrading and integrating the existing seismological observatories operated by various other agencies together with setting up a number of new observatories in the instrumental gap areas.

 

Key words  - Optimum design network, Earthquake monitoring, Detection capability, VSAT.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MAUSAM, 56, 3 (July  2005), 527-534

551.511.62 : 551.559 (541.1)

 

 

Parameterization of momentum and energy flux associated with

mountain wave across the Assam - Burma hills

 

SOMENATH DUTTA and NARESH KUMAR*

Meteorological Office, Pune – 411 005, India

*Meteorological Office, New Delhi – 110 003, India

(Received 23 December  2003, Modified 29 November 2004)

 

 

ABSTRACT. An attempt has been made to parameterize the energy flux and momentum flux associated with orographically excited internal gravity waves (IGW) across the Assam Burma Hills (ABH) in an idealized air stream. For this a two-dimensional meso-scale model has been developed and used to study the momentum/energy flux associated with vertically propagating orographically excited internal gravity waves for an idealized air stream characteristic, where both wind and stability of the prevailing flow remain invariant with height. Here the barrier is assumed to be extending semi infinitely in the cross-prevailing flow direction.

 

The above model is then applied to the ABH to compute the fluxes across it. The study shows that both the fluxes are independent of height, the energy flux is upward and momentum flux is downward. Following salient results are found from the study.

 

Wave momentum flux is vertically downward and wave energy flux is vertically upward for a vertically propagating mountain wave across the ABH.

 

It is found that the directions of vertical fluxes across the valley between the two ridges of the ABH are opposite to those across the two ridges and across the entire ABH.

               

This study also shows that a long valley (length of the valley exceeds the sum of the half widths of individual ridges, separated by the valley) acts as a source in the atmospheric momentum budget and as a sink in the atmospheric energy budget.

 

From the cases studied, it is found that the downward momentum flux (averaged over a length of 100 km along the flow) across the entire ABH varied between 4.5 – 10.0 Nm-2 and that across the two ridges varied between 2.0 - 7.0 Nm2 and upward momentum flux across the valley varied between 0.5 - 1.2 Nm-2. It is also found that the upward energy flux (averaged over a length of 100 km along the flow) across the entire Assam- Burma hill varied between 45.0 - 180.0 Wm-2 and that across the two ridges varied between 20.0 - 125.0 Wm-2 and downward energy flux across the valley varied between 5.0 - 21.0 Wm-2.

 

For the ABH, magnitude of both the fluxes increases with height but decreases with half with of the individual ridges.

 

Key words – Orographically excited internal gravity waves, ABH, Momentum flux, Energy flux.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MAUSAM, 56, 3 (July  2005), 535-542

551.509.324.2 (235.243)

 

Point probabilistic prediction of precipitation and quantitative

precipitation forecast in Western Himalayas