Diurnal and seasonal variations of the oh (8, 3) airglow band and its correlation with OI 5577 Å

In this paper the results of OH (8,3) emission intensity and rotational temperature measurements made in the Brazilian sector (23°S) from 1972 to 1974 are presented. Diurnal variations of both the parameters are found to fall into distinct classes, showing significant seasonal effects. A correlative study with the OI 5577 Å emission measured simultaneously is also presented. It is shown that both the phase and amplitude of the major part of the mean nocturnal intensity variations of the two emissions can be explained by the density and temperature perturbations caused by the solar semidiurnal tide. The OH emission is found to increase slightly during magnetic disturbances.     

Mesospheric energy loss rates by OH and C2 emissions at 23°S

The nightglow OH(9,4) and O₂ atmospheric (0,1) band emission intensities and their rotational temperatures T(OH) and T(O₂), respectively, observed at Cachoeira Paulista (23° S, 45°W), Brazil, during the period from October 1989 to December 1990, have been analyzed to study the nighttime mesospheric energy loss rates through the radiations from the vibrationally excited OH* and electronically excited O*₂ bands. The total emission rates of the OH Meinel bands, O₂ atmospheric (0,0) and O₂ infrared atmospheric (¹_g) bands were calculated using reported data for the relative band intensities and . It was found that there is a minimum in equivalent energy loss rate by the OH* Meinel bands during December/January (equivalent energy loss rate of 0.39 K/day*, where day* means averaged over the night) and maximum in equivalent energy loss rate during September (equivalent energy loss rate of 0.98 K/day*). Energy loss rate by the O*₂ radiation, on the other hand, is weaker than that by the OH* Meinel bands, showing equivalent energy loss rates of 0.12 K/day* and 0.22 K/day* during January and September, respectively.     

Strain and Crystallographic Fabric in Mesoscopic Ductile Shear Zones of Garhwal Himalaya

The MCT Zone of Bhagirathi valley of Garhwal Himalaya is characterized by numerous mesoscopic ductile shear zones. These shear zones are developed in response to nearly NNE-SSW maximum horizontal compression and provide an opportunity to study the variation in strain and crystallographic fabrics within the ductile shear zones.The grain shape and orientation of quartz under microscope reflect that strain is higher in the center and it progressively decreases towards the shear zone boundary. The preferred orientation of quartz c-axes across the shear zone suggests that the single girdle of the quartz c-axes are probably first developed at the shear zone boundary and become prominent in the center of shear zone with increase in the intensity of deformation. The strong crystallographic preferred orientation normal to foliation suggests that the internal deformation of the quartz might have taken place by dislocation creep mechanism exhibiting a non-coaxial deformation history.     

The effects of Mg and H on apatite nucleation at silica surfaces

Apatite (Ca₁₀[PO₄]₆[OH]₂) precipitation from aqueous solutions involves multiple steps, such as nucleation of a precursor calcium phosphate phase, cluster aggregation, crystal growth, and transformation to apatite, which are affected by the presence of other ions in solution. I report the mechanisms by which two ions common in natural solutions, Mg²⁺ and H⁺, affect heterogeneous calcium phosphate nucleation on the amorphous silica surface.     

Improvement in Precision of Crop Acreage Estimation by Remote Sensing Using Frequency Distribution Based Stratification

A study was conducted to improve precision of crop acreage adopting stratified random sampling approach. Remotely sensed data was used to classify mustard crop for the states of Rajasthan, Madhya Pradesh, Uttar Pradesh, Gujarat and Haryana covering 81% of mustard area of India. A grid of size 5 × 5 km was super-imposed on classified image of study area and proportion of mustard crop within the grid was ascertained. Crop proportion was used to determine strata. Stratification was done based on equal interval of proportion, equal sample number and cumulative square root of frequency method. Cumulative square root of frequency method gave highest precision in all the cases.     

Teleconnections in recent time and prediction of Indian summer monsoon rainfall

Summary The prediction of Indian Summer Monsoon Rainfall (ISMR) is vital for Indian economic policy and a challenge for meteorologists. It needs various predictors among which El Niño-Southern Oscillation (ENSO) is the most important. It has been established by various researchers that ENSO and ISMR relationship is weakening in recent years. It has been also argued that changes in ENSO-ISMR relationship may be due to decadal fluctuations, or it may be the indicative of longer-term trends related to anthropogenic-induced climate changes.In the present communication, an attempt is made to discuss the variability and predictability of ISMR in recent years. It is found that three different indices associated with different regions in the tropics and extra-tropics at different levels of the atmosphere-Asian land mass index represented by geopotential height at upper troposphere (A1), Caribbean-North Atlantic index represented by geopotential height at middle troposphere (A2) and tropical Pacific index at surface level (A3) – have different mechanisms to interact mutually and separately with ISMR in different periods. In recent years ISMR shows weak association with A1 and A3 while strong association with A2. Thus, if these three indices could be combined objectively, they can give rise to the predictability of ISMR. This objective combination is achieved here using Artificial Neural Network (ANN) and a model is developed to predict ISMR. This model has predicted reasonably well during the whole period of consideration (1958–2000) with a correlation coefficient of 0.92 in last 11 years (1990–2000) whereas most of the models fail to predict the variability in recent time.Current affiliation: Department of Physics, Federal University of Parana, Curitiba, Brazil.Received June 2002; revised October 1, 2002; accepted November 12, 2002 Published online: April 10, 2003     

Assimilation of Doppler Weather Radar Radial Velocity and Reflectivity Observations in WRF-3DVAR System for Short-Range Forecasting of Convective Storms

In this paper the impact of Doppler weather radar (DWR) reflectivity and radial velocity observations for the short range forecasting of a tropical storm and associated rainfall event have been examined. Doppler radar observations of a tropical storm case that occurred during 29–30 October 2006 from SHARDWR (13.6° N, 80.2° E) are assimilated in the WRF 3DVAR system. The observation operator for radar reflectivity and radial velocity is included within latest version of WRF 3DVAR system. Keeping all model physics the same, three experiments were conducted at a horizontal resolution of 30?km. In the control experiment (CTRL), NCEP Final Analysis (FNL) interpolated to the model grid was used as the initial condition for 48-h free forecast. In the second experiment (NODWR), 6-h assimilation cycles have been carried out using all conventional (radiosonde and surface data) and non-conventional (satellite) observations from the Global Telecommunication System (GTS). The third experiment (DWR) is the same as the second, except Doppler radar radial velocity and reflectivity observations are also used in the assimilation cycle. Continuous 6-h assimilation cycle employed in the WRF-3DVAR system shows positive impact on the rainfall forecast. Assimilation of DWR data creates several small scale features near the storm centre. Additional sensitivity experiments were conducted to study the individual impact of reflectivity and radial velocity in the assimilation cycle. Radar data assimilation with reflectivity alone produced large analysis response on both thermodynamical and dynamical fields. However, radial velocity assimilation impacted only on dynamical fields. Analysis increments with radar reflectivity and radial velocity produce adjustments in both dynamical and thermodynamical fields. Verification of QPF skill shows that radar data assimilation has a considerable impact on the short range precipitation forecast. Improvement of the QPF skill with radar data assimilation is more clearly seen in the heavy rainfall (for thresholds >7?mm) event than light rainfall (for thresholds of 1 and 3?mm). The spatial pattern of rainfall is well simulated by the DWR experiment and is comparable to TRMM observations.     

Diabatic heating profiles over the continental convergence zone during the monsoon active spells

The present paper aims to bring out the robust common aspects of spatio-temporal evolution of diabatic heating during the monsoon intraseasonal active phases over the continental tropical convergence zone (CTCZ). The robustness of spatio-temporal features is determined by comparing the two state-of-the art reanalyses: NCEP Climate Forecast System reanalysis and Modern ERA Retrospective Analysis. The inter-comparison is based on a study period of 26 years (1984–2009). The study confirms the development of deep heating over the CTCZ region during the active phase and is consistent between the two datasets. However, the detailed temporal evolution of the vertical structure (e.g., vertical tilts) of heating differs at times. The most important common feature from both the datasets is the significant vertical redistribution of heating with the development of shallow (low level) heating and circulation over the CTCZ region 3–7 days after the peak active phase. The shallow circulation is found to be associated with increased vertical shear and relative vorticity over certain regions in the subcontinent. This increased vertical shear and relative vorticity in the lower levels could be crucial in the sustenance of rainfall after the peak active phase. Model experiments with linear dynamics affirm the role of shallow convection in increasing the lower level circulation as observed.