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Parametrization Used (parametrization + used)

Distribution by Scientific Domains
Earth and Environmental Science100%

Selected Abstracts

Multiscale estimation of GPS velocity fields

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2009
Carl Tape
SUMMARY We present a spherical wavelet-based multiscale approach for estimating a spatial velocity field on the sphere from a set of irregularly spaced geodetic displacement observations. Because the adopted spherical wavelets are analytically differentiable, spatial gradient tensor quantities such as dilatation rate, strain rate and rotation rate can be directly computed using the same coefficients. In a series of synthetic and real examples, we illustrate the benefit of the multiscale approach, in particular, the inherent ability of the method to localize a given deformation field in space and scale as well as to detect outliers in the set of observations. This approach has the added benefit of being able to locally match the smallest resolved process to the local spatial density of observations, thereby both maximizing the amount of derived information while also allowing the comparison of derived quantities at the same scale but in different regions. We also consider the vertical component of the velocity field in our synthetic and real examples, showing that in some cases the spatial gradients of the vertical velocity field may constitute a significant part of the deformation. This formulation may be easily applied either regionally or globally and is ideally suited as the spatial parametrization used in any automatic time-dependent geodetic transient detector. [source]

Testing a cumulus parametrization with a cumulus ensemble model in weak-temperature-gradient mode

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 626 2007
D. J. Raymond
Abstract This paper prototypes a method for calibrating a cumulus parametrization against a cumulus ensemble model. The key to this technique is to run the cumulus model and the parametrization in identical ,test cells' that provide forcing typical of that seen over tropical oceans. In particular, the mean temperature profile is relaxed to a reference profile that is assumed to be characteristic of the environment of the convection. This is done by calculating the mean vertical velocity needed to balance heating due to convection, latent-heat release, and radiation with adiabatic cooling. This ,weak-temperature-gradient' vertical-velocity profile is then used to advect moisture vertically and, via mass continuity, through the sides of the test cell, entraining reference-profile air as needed. As an example, a toy cumulus parametrization used previously is altered to reproduce the dependence of rainfall rate on surface wind speed shown by the cumulus ensemble model. This alteration greatly changes the behaviour of simulated large-scale disturbances in an aquaplanet equatorial beta-plane model. In particular, increasing the slope of the curve of rainfall rate against wind speed results in the development of much greater synoptic-scale variance. Copyright © 2007 Royal Meteorological Society [source]

Cloud-resolving model simulations of multiply-banded frontal clouds

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 611 2005
M. Pizzamei
Abstract An idealized two-dimensional cloud-resolving model is used to investigate the formation and temporal evolution of multiply-banded clouds in frontal zones. Radar observations often show both upright and slantwise convection in the circulations associated with such bands. The aim is to examine the interaction between upright and slantwise convection and to determine the mechanisms leading to multiple banding. A warm bubble is used to initiate convection in the frontal zone, which has an initial thermodynamic profile based on observations. Further triggering occurs and banded clouds evolve. The initially upright plumes become tilted due to the so-called ,M adjustment process (upscale development). Observed multiple bands in frontal zones are frequently attributed to the release of conditional symmetric instability (CSI). However, in these simulations, there is no evidence of the release of CSI despite the fragmentation of slantwise bands into multiple layers in the mid-troposphere. Successive triggering of upright convection is instead associated with a spreading cold pool driven by evaporative cooling in the slanted downdraughts. Triggering can occur on both the warm- and cold-air sides of the frontal zone, and is sensitive to the microphysical parametrization used. Copyright © 2005 Royal Meteorological Society. [source]

Orographic flow-blocking scheme characteristics

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 603 2004
A. R. Brown
Abstract The characteristics of the orographic flow blocking parametrization used in the Met Office Unified Model are examined in a one-dimensional framework. This approach allows feedback of the parametrized stresses on the winds resulting, in some cases, in stresses very different from those that would be obtained without this feedback. The key controlling non-dimensional parameters are identified, and the implications of the results for the use of the scheme in climate and numerical weather-prediction models are discussed. Copyright © 2004 Royal Meteorological Society [source]

Large-eddy simulation of the diurnal cycle of shallow cumulus convection over land

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 582 2002
A. R. Brown
Abstract Large-eddy simulations of the development of shallow cumulus convection over land are presented. Many characteristics of the cumulus layer previously found in simulations of quasi-steady convection over the sea are found to be reproduced in this more strongly forced, unsteady case. Furthermore, the results are shown to be encouragingly robust, with similar results obtained with eight independent models, and also across a range of numerical resolutions. The datasets produced are already being used in the development and evaluation of parametrizations used in numerical weather-prediction and climate models. © Royal Meteorological Society, 2002. A. R. Brown's, A. P. Lock's and M. K. MacVean's contributions are Crown copyright. [source]