The Convective Storm Initiation Project

ABSTRACT:Observations from the Convective Storm Initiation Project (CSIP) show that on 29 June 2005 (Intensive Observation Period 5) cirrus patches left over from previous thunderstorms reduced surface sensible and latent heat fluxes in the CSIP area. Large-eddy model (LEM) simulations, using moving positive surface-flux anomalies, show that we expect the observed moving gaps in the cirrus cover to significantly aid convective initiation. In these simulations, the timing of the CI is largely determined by the amount of heat added to the boundary layer, but weak convergence at the rear edge of the moving anomalies is also significant.Meteosat and rain-radar data are combined to determine the position of convective initiation for all 25 trackable showers in the CSIP area. The results are consistent with the LEM simulations, with showers initiating at the rear edge of gaps, at the leading edge of the anvil, or in clear skies, in all but one of the cases. The initiation occurs in relatively clear skies in all but two of the cases, with the exceptions probably linked to orographic effects.For numerical weather prediction, the case highlights the importance of predicting and assimilating cloud cover. The results show that in the absence of stronger forcings, weak forcings, such as from the observed cirrus shading, can determine the precise location and timing of convective initiation. In such cases, since the effects of shading by cirrus anvils from previous convective storms are relatively unpredictable, this is expected to limit the predictability of the convective initiation.

Section: Analysis Of Observed Convective Initiation In the Csip Areamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Variable cirrus shading during CSIP IOP 5. I: Effects on the initiation of convection

Marsham

Morcrette

Browning

et al. 2007

“…the dryline) for improving the prediction of warmseason rainfall (Weckwerth and Parsons, 2006). The CSIP was an international project to understand where, when and how convective clouds form and develop into showers in the mainly maritime environment of southern England (Browning et al, 2007). In contrast, precipitation in the COPS region covering low-mountain regions in southwestern Germany/eastern France is due to a complex interaction between large-scale instabilities, modification of mesoscale flow by orography, and thermally induced orographic flow.…”

Section: Introductionmentioning

confidence: 99%

The Convective and Orographically‐induced Precipitation Study (COPS): the scientific strategy, the field phase, and research highlights

Wulfmeyer

Behrendt

Kottmeier

et al. 2011

Self Cite

193

136

Within the framework of the international field campaign COPS (Convective and Orographically-induced Precipitation Study), a large suite of state-of-the-art meteorological instrumentation was operated, partially combined for the first time. This includes networks of in situ and remote-sensing systems such as the Global Positioning System as well as a synergy of multi-wavelength passive and active remote-sensing instruments such as advanced radar and lidar systems. The COPS field phase was performed from 01 June to 31 August 2007 in a low-mountain area in southwestern Germany/eastern France covering the Vosges mountains, the Rhine valley and the Black Forest mountains. The collected data set covers the entire evolution of convective precipitation events in complex terrain from their initiation, to their development and mature phase until their decay. Eighteen Intensive Observation Periods with 37 operation days and eight additional Special Observation Periods were performed, providing a comprehensive data set covering different forcing conditions. In this article, an overview of the COPS scientific strategy, the field phase, and its first accomplishments is given. Highlights of the campaign are illustrated with several measurement examples. It is demonstrated that COPS research provides new insight into key processes leading to convection initiation and to the modification of precipitation by orography, in the improvement of quantitative precipitation forecasting by the assimilation of new observations, and in the performance of ensembles of convection-permitting models in complex terrain.

“…The above-mentioned details of the evolution were not so well reproduced but, nevertheless, sensitivity studies with the model provide some insight into the important processes operating during the event. Browning et al (2007) show the locations of the numerous observational instruments deployed in southern Britain during the campaign. The CSIP campaign was centred on the Chilbolton observatory.…”

Section: Introductionmentioning

confidence: 99%

The evolution of an MCS over southern England. Part 1: Observations

Clark

Browning

Morcrette

et al. 2013

The observed MCS structure broadly followed well-established theories, including the presence of a weak rear-inflow jet. In detail, however, unsteady transitions occurred involving the formation of two distinct lines of showers ahead of the initial linear system. In each case the cold pool merged with cold downdraughts from the new showers leading to a discontinuous propagation of the system. One of these lines formed independently of the MCS, very probably on a sea-breeze convergence line. The mechanism for formation of the other is unknown, but it is possible that it was triggered by ascent associated with gravity waves generated by the MCS. The merged cold pool was deeper and colder and propagated faster than the original system, eventually forming a bow echo and arc cloud as it propagated across the English Channel. Until completion of the merger, the propagation velocity of the overall system had been controlled by a combination of the above mechanisms rather than simply by cold pool dynamics.