K. E. Bozier

The Convective Storm Initiation Project

The Convective Storm Initiation Project (CSIP) is an international project to understand precisely where, when, and how convective clouds form and develop into showers in the mainly maritime environment of southern England. A major aim of CSIP is to compare the results of the very high resolution Met Office weather forecasting model with detailed observations of the early stages of convective clouds and to use the newly gained understanding to improve the predictions of the model. A large array of ground-based instruments plus two instrumented aircraft, from the U.K. National Centre for Atmospheric Science (NCAS) and the German Institute for Meteorology and Climate Research (IMK), Karlsruhe, were deployed in southern England, over an area centered on the meteorological radars at Chilbolton, during the summers of 2004 and 2005. In addition to a variety ofground-based remote-sensing instruments, numerous rawinsondes were released at one- to two-hourly intervals from six closely spaced sites. The Met Office weather radar network and Meteosat satellite imagery were used to provide context for the observations made by the instruments deployed during CSIP. This article presents an overview of the CSIP field campaign and examples from CSIP of the types of convective initiation phenomena that are typical in the United Kingdom. It shows the way in which certain kinds of observational data are able to reveal these phenomena and gives an explanation of how the analyses of data from the field campaign will be used in the development of an improved very high resolution NWP model for operational use.

Doppler lidar measurements of turbulent structure function over an urban area

Analysis of radial wind velocity data from the Salford pulsed Doppler infrared lidar is used to calculate turbulent spectral statistics over the city of Salford in the United Kingdom. The results presented here, first, outline the error estimation procedure used to correct the radial wind velocity measurements from the Salford lidar system; second, they correct the data for the spatial averaging effects of the Salford lidar pulse; and finally, they use the corrected data to calculate turbulent spectral statistics. Using lidar data collected from the Salford Urban Meteorological Experiment (SALFEX), carried out in May 2002, kinetic energy dissipation rates, radial velocity variance, and integral length scales are calculated for the boundary layer above an urban canopy. The estimates of the kinetic energy dissipation rate from this method are compared to calculations using more traditional spectral methods. The estimates of the kinetic energy dissipation rate for the two methods are correlated and both show an increase in dissipation rate through the day. The procedure followed for the correction of the spatial averaging effects of the lidar pulse shape actually uses the Salford lidar pulse shape profile.

Dual-Doppler Lidar Measurements for Improving Dispersion Models

Abstract Dispersion of pollutants in the urban atmosphere is a subject that is presently under much investigation. In this paper the variables used in turbulent dispersion and plume rise schemes of the Met Office Nuclear Accident Model (NAME) are discussed. Those parameters that can be measured by Doppler lidar are emphasized. Information derived from simultaneous measurements from two Doppler lidars are presented, using methodologies not tried previously, with the aim of improving the forecasting of urban pollution dispersion. The results demonstrate how Doppler lidars can be used as measuring tools for the specific parameters needed within urban dispersion models. A procedure used for carrying out the dual-lidar measurements is outlined. This research shows how dual-lidar measurements can be used to calculate the relevant dispersion parameters, and compares the dual-lidar measurements with model calculations in a case study. Differences between model parameters and lidar observations are discussed. Dual...

Errors associated with dual-Doppler-lidar turbulence measurements

In July 2004 a field trial was undertaken to simultaneously deploy two similar Doppler lidar systems with the aim of measuring the turbulence characteristics of the atmospheric boundary layer over an urban area. This paper outlines the characteristics of the lidar systems, details the deployment configuration of the lidars, and discusses the dispersion model parameters that can be obtained using this procedure. An error analysis is undertaken to highlight the possible problems associated with the derived data. A case study from the trial is shown to compare the dual-lidar derived data to dispersion model results from the NAME dispersion model.

Evaluating the precision of a transverse excitation atmospheric based CO2 Doppler lidar system with in situ sensors

A ground based, mobile, scanning Doppler lidar system used for atmospheric boundary layer research is described. The system is designed to operate safely in urban areas and has an eye safe wavelength of 10.6 µm, a range capability of up to 9 km (dependent on atmospheric conditions) and a range resolution of 112 m. Results are presented from an intercomparison campaign that was undertaken in September 2002 to compare several UFAM (UK Universities Facilities for Atmospheric Measurements) instruments with traditional in situ balloon borne instrumentation. A comparison between lidar and balloon derived horizontal wind profiles is given along with an estimation of the magnitude of the random error in the lidar Doppler velocity estimates. Measurements were made over heterogeneous terrain up to a height of 1 km, with a maximum velocity difference of 0.53 m s-1 between the derived wind profiles over a height range of 400 m. The magnitude of the random error in the velocity estimates was found to be 0.41 m s-1 for a signal to noise greater than -6 dB. Keywords: Doppler lidar, atmospheric boundary layer