Atmospheric Science Letters

A high resolution daily gridded temperature data set for the Indian region was developed using temperature data of 395 quality controlled stations for the period 1969–2005. A modified version of the Shepard's angular distance weighting algorithm was used for interpolating the station temperature data into 1° latitude × 1° longitude grids. Using the cross validation, errors were estimated and found less than 0.5 °C. The data set was also compared with another high resolution data set and found comparable. Mean frequency of cold and heat waves, temperature anomalies associated with the monsoon breaks have been presented. Copyright © 2009 Royal Meteorological Society

The critical Richardson number, Ri_c, is used in studies of stably stratified turbulence as a measure of flow laminarization. The accepted range of Ri_c is between 0.2 and 1. A growing body of experimental and observational data indicates, however, that turbulence survives for Ri ≫ 1. This result is supported by a new spectral theory of turbulence that accounts for strong anisotropy and waves. The anisotropization results in the enhanced horizontal mixing of both momentum and scalar. Internal wave contribution preserves vertical momentum mixing above its molecular level. In the absence of laminarization, Ri_c becomes devoid of its conventional meaning. Copyright © 2007 Royal Meteorological Society

The Hydrologist's traditional tool for measuring rainfall is the rain gauge. Rain gauges are relatively cheap, easy to maintain and provide a direct and suitably accurate estimate of rainfall at a point. What rain gauges fail to capture well is the spatial variability of rainfall with time, an important aspect for the credible modelling of a catchment's response to rainfall. This spatial variability is particularly evident at short timescales of up to several days. As the period of accumulation increases, the expected spatial variability is reduced and rain gauges provide improved spatial rainfall estimates. Because of the fractal variability of rainfall in space, simple interpolation between rain gauges does not provide an accurate estimate of the true spatial rainfall field, at short time scales.

Weather radar provides (with a single instrument) a highly detailed representation of the spatial structure and temporal evolution of rainfall over a large area. Estimated rainfall rates are derived indirectly from measurements of reflectivity and are therefore subject to a combination of systematic and random errors.

This article describes a recently proposed merging technique and presents an application to simulated rainfall fields. The technique employed is Conditional Merging (Ehret, 2002), which makes use of Kriging to extract the optimal information content from the observed data. A mean field based on the Kriged rain gauge data is adopted, while the spatial detail from the radar is retained, reducing bias, but keeping the spatial variability observed by the radar. The variance of the estimate is reduced in the vicinity of the gauges where they are able to provide good information on the true rainfall field. Copyright © 2005 Royal Meteorological Society

The characteristics of aerosol black carbon (BC) were studied at two different climatic regimes, i.e. Delhi and Manora Peak during winter and spring of 2007. Spring BC was found to be ∼59% lower at Delhi and ∼23% higher at Manora Peak than their corresponding winter BC. Diurnal BC variation showed two enhanced peaks at Delhi (morning and night) whereas a single late afternoon peak at Manora Peak. Delhi BC showed a clear correlation with prevailing winds whereas no correlation was observed at Manora Peak. The major contribution of BC at Manora Peak can be expected from biomass burning while at Delhi fossil fuel dominates. Copyright © 2012 Royal Meteorological Society

Time variations and large‐scale features of South America summer monsoon are characterized by an index based on the first combined EOF of anomalies of precipitation, specific humidity, air temperature, and zonal and meridional winds at 850 hPa. This index describes intraseasonal to interannual variations of the monsoon. Copyright © 2007 Royal Meteorological Society

NOAA 20th century and ERA‐20C reanalysis datasets are evaluated regarding the representation of extra‐tropical cyclones and windstorms over the Northern and Southern Hemisphere during the respective 6‐month winter seasons. The results indicate substantial differences in low‐frequency variability between the two datasets – especially in the first half of the 20th century – expressed in different signs and/or magnitudes of long‐term trends. This is hampering a reliable analysis of real long‐term trends of cyclone and windstorm activity. However, higher‐frequency variability is in good agreement between both datasets especially for the Northern Hemisphere.

Residual kriging (RK) is applied to data from measurements performed with an instrumented motorglider in an Alpine Valley, where a coupled lake and valley wind develops. Results provide an insight into a typical mean vertical structure of the valley boundary layer, displaying a rather shallow convective mixed layer, surmounted by a deep stable layer. Mapping with RK allows to detect spatial temperature anomalies associated with the local development of diurnal winds over each explored valley cross section. Local scale features, such as cross‐valley thermal asymmetries, amenable to surface inhomogeneities and their effects on heat fluxes, are also identified. Copyright © 2013 Royal Meteorological Society

The relationship between catchment rainfall, evapotranspiration and runoff can be exploited to assess climate risk to water resources. National data regarding climatology and runoff were used to estimate the sensitivity of regional runoff to projected changes in precipitation and evaporation. These sensitivity factors were integrated with patterns of climate change from 12 different global climate model (GCM) simulations to project future annual runoff sensitivity per degree of global mean temperature change. Divergent runoff sensitivities were identified depending upon the selected GCM. Averaging among GCMs resulted in a robust pattern of runoff sensitivity suitable for estimating future climate risk. Copyright © 2008 Royal Meteorological Society

Based on the European Centre for Medium‐Range Weather Forecasts (ECMWF) ERA5 reanalysis data, in this study, formation mechanisms of a severe windstorm that caused successive trippings of the transmission lines in Southern Xinjiang were investigated. The strong windstorm occurred within a lower‐tropospheric warm region due to adiabatic heating of the descending motions ahead of a shortwave trough in the westerly wind (the blocking effects of high mountain was a key reason for the strong descending motions). The kinetic energy (KE) budget indicates two typically different stages appeared in the variation of the windstorm. The former stage showed a rapid wind KE enhancement in the lower troposphere. The KE increase was mainly governed by the downward stretching of high KE (i.e., downward momentum transportation) from the middle troposphere (rather than from the upper‐level jet) and the KE production due to the work on rotational wind by the pressure gradient force. The latter stage showed a rapid KE decrease mainly due to the transport of KE by the rotational wind and the pressure gradient force's negative work on the rotational wind. In contrast, the vertical advection of KE still acted as transporting high KE from middle troposphere to lower troposphere, which resisted the KE reduce at the lower levels.

We show that the standard deviation of the distribution from which changes in the ensemble mean are drawn can be predicted using the ensemble spread. Such a forecast has direct application for companies that trade weather swaps and need to evaluate their risk. Copyright © 2003 Royal Meteorological Society. Published by Elsevier Ltd. All rights reserved.