Fay Davies

An Analysis of the Performance of the UFAM Pulsed Doppler Lidar for Observing the Boundary Layer

Abstract The performance of the 1.5-μm pulsed Doppler lidar, operated by the U.K. Universities Facility for Atmospheric Measurement (UFAM) over a 51-day continuous and unattended field deployment in southern England, is described and analyzed with a view to demonstrating the capabilities of the system for remote measurements of aerosols and velocities in the boundary layer. A statistical assessment of the vertical pointing mode in terms of the availability and errors in the data versus range is presented. Examples of lidar data are compared to theoretical predictions, radiosondes, the UFAM radar wind profiler, and an ultrasonic anemometer.

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.

A Method for Estimating the Turbulent Kinetic Energy Dissipation Rate from a Vertically Pointing Doppler Lidar, and Independent Evaluation from Balloon-Borne In Situ Measurements

Abstract A method of estimating dissipation rates from a vertically pointing Doppler lidar with high temporal and spatial resolution has been evaluated by comparison with independent measurements derived from a balloon-borne sonic anemometer. This method utilizes the variance of the mean Doppler velocity from a number of sequential samples and requires an estimate of the horizontal wind speed. The noise contribution to the variance can be estimated from the observed signal-to-noise ratio and removed where appropriate. The relative size of the noise variance to the observed variance provides a measure of the confidence in the retrieval. Comparison with in situ dissipation rates derived from the balloon-borne sonic anemometer reveal that this particular Doppler lidar is capable of retrieving dissipation rates over a range of at least three orders of magnitude. This method is most suitable for retrieval of dissipation rates within the convective well-mixed boundary layer where the scales of motion that the D...

COLPEX: Field and Numerical Studies over a Region of Small Hills

During stable nighttime periods, large variations in temperature and visibility often occur over short distances in regions of only moderate topography. These are of great practical significance and yet pose major forecasting challenges because of a lack of detailed understanding of the processes involved and because crucial topographic variations are often not resolved in current forecast models. This paper describes a field and numerical modeling campaign, Cold-Air Pooling Experiment (COLPEX), which addresses many of the issues. The observational campaign was run for 15 months in Shropshire, United Kingdom, in a region of small hills and valleys with typical ridge–valley heights of 75–150 m and valley widths of 1–3 km. The instrumentation consisted of three sites with instrumented flux towers, a Doppler lidar, and a network of 30 simpler meteorological stations. Further instrumentation was deployed during intensive observation periods including radiosonde launches from two sites, a cloud droplet probe, ...

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.

Combining active and passive airborne remote sensing to quantify NO2 and Ox production near Bakersfield, CA.

Aims: The objective of this study is to demonstrate the integrated use of passive and active remote sensing instruments to quantify the rate of NO x emissions, and investigate the O x production rates from an urban area. Place and Duration of Study: A research flight on June 15, 2010was conducted over Bakersfield, CA and nearby areas with oil and natural gas production. Methodology: Three remote sensing instruments, namely the University of Colorado AMAX-DOAS, NOAA TOPAZ lidar, and NCAS Doppler lidar were deployed aboard the NOAA Twin Otter during summer 2010. Production rates of nitrogen dioxide (NO 2) and background corrected O x (background corrected O 3 + NO 2), O x’ were quantified using the horizontal flux divergence approach by flying closed loops near Bakersfield, CA. By making concurrent measurements of the trace gases as well as the wind fields, we have greatly reduced the uncertainty due to wind field in production rates. Results: We find that the entire region is a source for both NO 2 and O x’. NO 2 production

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

Evaluation of dispersion model parameters by dual Doppler lidars over West London, England

Urban dispersion models have parameters for the turbulence and mixing height. We identify the parameters in meteorological pre-processors, which are, in principle, measurable by pulsed Doppler lidar. This technique measures radial velocity from the Doppler shifted wavelengths of backscattered laser pulses. First results obtained from single and dual lidar operations are described. Using two scanning lidars increases the range of parameters that can be sensed remotely. Scanned Dual Doppler lidar provides a novel remote sensing method for studying the rural-urban interface. Results are presented from a recent field experiment at an airfield site in West London. Results are compared with data from the Met Office operational dispersion model, NAME, a model using numerical weather forecast data. We show three methods for the urban mixing height. The paper concludes by considering the potential merits of dual-lidar remote sensing of urban dispersion model parameters.