No abstract

To study why, where, and when deep convection

Abstract. The Convective Storm Initiation Project (CSIP) took place during the summers of 2004 and 2005, centred on the research radar at Chilbolton, UK. Precursors to convective precipitation were studied, using a comprehensive and broad-based range of fieldwork and modelling. The principal aim of CSIP was the detection of the primary and secondary initiation of convective cells. The Universities Facility for Atmospheric Measurements (UFAM) Cessna 182 was used to map temperature and humidity fields over a broad area within and beyond the Chilbolton radar beam. Additionally, air motion was measured using a new turbulence probe, the AIMMS20AQ. The performance of the probe is critically appraised, based on calibrations, test flights and data flights flown during CSIP intensive operating periods. In general, the probe performed well, although some aspects require more careful data interpretation which we describe in detail.

Some of the most damaging surface winds experienced in midlatitude cyclonic storms have been attributed to a phenomenon known as a sting jet. Previous studies have deduced how sting jets develop from their midtropospheric origin, but there have been no direct observations of these wind features in the midtroposphere. During Windstorm Jeanette on 27 October 2002, the tip of the storm's cloud head passed over a VHF wind profiler at Aberystwyth, Wales, allowing the structure of a sting jet to be measured with high spatial and temporal resolution. These observations showed a multiple slantwise structure to the sting jet region, with two tails of increased winds that persisted after the passing of the cloud head aloft. Simulations by the Met Office Unified Model (UM) showed that the slantwise structure followed θ w surfaces, and that the sting jet descended along θ surfaces as it passed over the UK, accelerating and drying during its descent. The horizontal and vertical scales of the observed structures are compatible with slantwise convection releasing conditional symmetric instability within the cloud head. Further observations of the sting jet were obtained by a UHF wind profiler at Cardington in Eastern England, where the sting jet had merged with the cold conveyor belt circulating around the storm. An unstable temperature profile in the lowest kilometre over Cardington enabled damaging gusts of strong winds to be brought to the surface in convective plumes; however, this strong vertical mixing was not represented correctly in the UM.