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doi: 10.1002/qj.49712152702pmid: N/A
Measurements of the microwave brightness temperature of stratocumulus cloud at 89 and 157 GHz using the Microwave Airborne Radiometer Scanning System on the UK Meteorological Research Flight's C‐130 aircraft have been analysed. Comparisons of observed and calculated brightness temperature using models available in the literature have given good agreement for sea‐surface emission and atmospheric attenuation in clear and cloudy skies. A nonlinear retrieval scheme has been applied to the observations to retrieve cloud liquid‐water paths for comparison with the in situ measurements. Validation of the retrieved liquid‐water paths to within 50 g m−2 has been achieved. Ambiguities between cloud retrievals and water vapour and surface parameters are discussed. the observed differences between the retrieval and the in situ measurement are not found to correlate strongly with cloud temperature, but a higher than expected correlation is found with the drop‐size distribution. It is demonstrated that the scheme is applicable to satellite soundings of cloud, and that a similar level of accuracy should be achieved.
Baker, Marcia B.; Christian, Hugh J.; Latham, John
doi: 10.1002/qj.49712152703pmid: N/A
In an effort to optimize the value of global‐scale measurements obtained with the NASA/MSFC satelliteborne Lightning Imaging System (LIS), a simple computational model of thundercloud electrification has been developed, from which it is possible to derive crude relationships between lightning frequency f (which LIS will measure) and cloud parameters such as radar reflectivity Z, precipitation rate P, updraught speed w, cloud radius R, ice‐crystal concentration i and graupel‐pellet concentration Ng. Electric field‐growth is assumed to occur via the non‐inductive charging mechanism, for both Fletcher and Hallett‐Mossop types of glaciation mechanisms. A simple criterion is used to distinguish between cloud‐to‐ground and intracloud lightning discharges. f is found to be especially sensitive to w in situations where, as updraught speed increases, the temperature at balance level, Tbal, of the upper boundary of the charging zone falls. In these circumstances N1 and the sizes of the ice hydrometeors are significantly increased, with a corresponding enhancement of the effectiveness of charge transfer.
doi: 10.1002/qj.49712152704pmid: N/A
Tethered‐balloon data collected over an inhomogeneous, semi‐rural area of central England are presented. the data are compared with previous surface data to assess how representative fixed‐point flux‐measurements are of area averages. the differences between the data and ‘established’ surface‐layer results are relatively small with departures of about 10% to 20%. This supports the concept of a blending height above which the flow becomes horizontally homogeneous. Effective roughness lengths for momentum and heat transfer are derived. the ratio zeff0m/zeff 0t is found to be about 80 compared to z0m/z0t ≈︁10 observed for homogeneous terrain. For different wind directions the relationship between the effective roughness length and the upwind surface is investigated using recent theories on the area‐averaging of surface roughness lengths. It is found that the method of averaging transfer coefficients gives realistic values of the effective roughness lengths when compared to observations.
Inglis, D. W. F.; Choularton, T. W.; Wicks, A. J.
doi: 10.1002/qj.49712152705pmid: N/A
Two field experiments were carried out to observe the variation in wet deposition of ions caused by orography in a polluted region of the UK. the site chosen was Winter Hill which lies on the edge of the industrialised Mersey valley. Rain and cloud samples were collected daily and chemically analysed. Synoptic and meteorological data were used to classify individual rain events as frontal or convective.
doi: 10.1002/qj.49712152706pmid: N/A
The nature of unstable easterly waves growing on three different easterly jets has been examined. the ‘shearjet’ with strongest horizontal mean shear on the equatorward side of the jet is characterized by linearly unstable waves with maximum amplitude equatorward of the jet maximum and are dominated by barotropic energy conversions associated with positive horizontal momentum fluxes. the normal modes of the shear‐jet have very little amplitude at the surface.
Smith, Gerald B.; Montgomery, Michael T.
doi: 10.1002/qj.49712152707pmid: N/A
Intense vortices in the atmosphere and ocean exhibit a high degree of axisymmetry despite persistent asymmetric forcing from their environment. to further elucidate vortex axisymmetrization a variety of idealized initial‐value models for barotropic non‐divergent flow is considered. to ensure basic understanding, disturbance evolution is first examined in a rectilinear system of simple shear. Particular emphasis is placed on identifying how inviscid disturbance‐evolution depends on the zonal wave‐number and on the meridional structure of the initial conditions.
Efimov, V. V.; Prusov, A. V.; Shokurov, M. V.
doi: 10.1002/qj.49712152708pmid: N/A
Results of the COADS data processing aimed at a classification of the structure of the large‐scale lowfrequency variability of the sea surface temperature, the sea‐level atmospheric pressure and the surface wind‐speed components are presented. Using cluster analysis, patterns of interannual variability in the temporal and spatial domains are obtained. Clusters consisting of points possessing similar temporal evolution are compared with the known dipole‐type patterns of interannual variability, and special attention is given to selection of the global ENSO‐related patterns. of particular interest are the teleconnection links between the equatorial and the extratropical regions in the Pacific Ocean. Clusters consisting of times with similar spatial patterns, as well as extended canonical correction analysis patterns, show the typical sequence of the spatial patterns during the ENSO cycle, especially for the ‘mature’ warm and cold phases. For these cases, typical features of the field anomalies, including the extratropical peculiarities in the Pacific Ocean, are considered and summarized.
doi: 10.1002/qj.49712152709pmid: N/A
For the first time, the method of four‐dimensional variational data assimilation is applied to the analysis of chemically active trace species. By combining observations with a numerical model to analyse simultaneously several species over a period of a few days, the analysis method is able to exploit information which is not available to conventional analysis techniques. Moreover, effective use can be made of asynoptic observations even for species which have strong diurnal cycles. Synoptic analyses are produced. A Lagrangian approach is adopted, allowing a separation of dynamics and chemistry which considerably reduces the computational expense of the method.
doi: 10.1002/qj.49712152710pmid: N/A
Certain characteristics of the perturbations which grow most rapidly over a finite time interval in a primitiveequation atmospheric model are discussed. They are the singular vectors of a linear approximation of the European Centre for Medium‐Range Weather Forecasts primitive‐equation model. They are computed using the adjoint technique at horizontal spectral truncation T21 with 19 vertical levels. Linear combinations of singular vectors, named optimal perturbations, can be used in ensemble prediction to generate the initial conditions of perturbed integrations.
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