S. H. Melfi

Inference of Marine Atmospheric Boundary Layer Moisture and Temperature Structure Using Airborne Lidar and Infrared Radiometer Data

Abstract A new technique for retrieving near-surface moisture and profiles of mixing ratio and potential temperature through the depth of the marine atmospheric boundary layer (MABL) using airborne lidar and multichannel infrared radiometer data is presented. Data gathered during an extended field campaign over the Atlantic Ocean in support of the Lidar In-space Technology Experiment are used to generate 16 moisture and temperature retrievals that are then compared with dropsonde measurements. The technique utilizes lidar-derived statistics on the height of cumulus clouds that frequently cap the MABL to estimate the lifting condensation level. Combining this information with radiometer-derived sea surface temperature measurements, an estimate of the near-surface moisture can be obtained to an accuracy of about 0.8 g kg−1. Lidar-derived statistics on convective plume height and coverage within the MABL are then used to infer the profiles of potential temperature and moisture with a vertical resolution of 2...

Cold-Air Outbreak during GALE: Lidar Observations and Modeling of Boundary Layer Dynamics

Abstract Two cold-air outbreaks were studied during the Genesis of Atlantic Lows Experiment. A lidar system was operated to observe the boundary layer evolution and the development of clouds. On the first day (30 January 1986) boundary layer rise was less than 50% of the value for the second day (2 March 1986). On the first day only a thin broken cloud cover formed, while on the second day a thick solid cloud deck formed—although the average moisture content was 60% of that on the first day. A trajectory slab model was employed to simulate the evolution of the layer over the ocean near the cast Atlantic shore. The model allows for vertical gradients in conservative variables under neutrally buoyant conditions. The primary effect of these assumptions, which are based on observed thermodynamic profiles, is to reduce cloudiness to be more in line with observations. Boundary layer depth was reasonably well predicted as was sensible and latent heat flux.

Estimating the Orientation and Spacing of Midlatitude Linear Convective Boundary Layer Features: Cloud Streets

AbstractLinear features in a clear convective boundary layer (CBL) over the North Atlantic Ocean were studied during a weak cold air outbreak using a down-looking airborne lidar. Sequential lidar profiles were placed together and color coded to provide images of aerosol and molecular scattering from below the aircraft to the ocean surface, over a 36-km segment of a flight track approximately 150 km off the coast of southern Virginia. The aircraft flew on a path approximately perpendicular to the expected orientation of cloud streets if they had formed. The lidar image clearly shows randomly sized convective cells in the CBL, grouping under the crests of a gravity wave in the stable troposphere. It is suggested that the wave develops as energetic convective cells in the CBL penetrate into the stable layer aloft and act as obstructions to the relative flow. An analytic study, published in 1965, demonstrates that vertical disturbances on the top of the CBL adjust to be in resonance with a horizontal gravity ...

Validation of LITE-derived Saharan dust layer characteristics

Lidar observations from the Lidar-in Space Technology Experiment (LITE), in conjunction with European Center for Medium Range Weather Forecasting (ECMWF) and Meteosat data were used to examine the Saharan dust characteristics including its structure, evolution and optical depths over Western Africa and E. Atlantic regions. The lidar backscatter profiles reveal a complex structure of the dust layer but, in general, show a good agreement with the features depicted in the conceptual model of the dust plume. Optical depths of the Saharan dust layer derived from two independent methods were compared with those obtained from the Meteosat data. Although the LITE-derived optical depth patterns from the two methods are in good agreement with each other, they show some differences with those derived from the satellite data, particularly in the inference of heavy dust concentration over the E. Atlantic.

Retrieval of Atmospheric Boundary Layer Parameters from LITE and LASAL

Five 2000 km long underflights of LITE were conducted with the NASA P3-B aircraft containing the Large Aperture Scanning Airborne Lidar (LASAL) system. We analyze the LASAL data to accurately recover the height of the convective boundary layer, entrainment zone thickness, and lifting condensation level. Using the LASAL algorithms on LITE data we evaluate the efficacy of spaceborne lidar in measuring boundary layer parameters.

Raman lidar measurements of cloud liquid water and droplet size

A new technique for measuring cloud liquid water, mean droplet radius and droplet number density has been presented elsewhere and is reviewed here. A new extension of the theory is then presented which allows multiple scattering to be quantified. The technique is based on simultaneously measuring Raman and Mie scattering from cloud liquid droplets using a Raman lidar. The intensity of Raman scattering is known to be proportional to the amount of liquid present in cloud droplets. This fact is used as a constraint on calculated Mie intensity to calculate droplet radius and number density. The technique is tested using Raman lidar data. The general relationship of retrieved average radius and number density is consistent with traditional cloud physics models.

Remote sensing of the marine atmospheric boundary layer and ocean surface winds: observations from the LITE correlative flights

The planetary boundary layer (PBL) is the lowest 1 km or so of the troposphere which directly interacts with the underlying surface. The fluxes of heat, moisture and momentum within the PBL are very important to weather forecasting and are in part determined by the mean wind speed and characteristics of the surface. Over the ocean, where the surface remains homogeneous over relatively large distances, the structure and height of the PBL are probably good indicators of the magnitude of the surface fluxes. This implies that changes in PBL height or convective intensity might be correlated with surface wind. The authors present simultaneous measurements of the height and convective structure of the PBL and surface (10 meter) wind speed derived from airborne lidar and microwave scatterometer instruments, respectively. They use these data to investigate the response of the PBL to changes in the wind speed over scales ranging from hundreds of kilometers (synoptic scale) to less than 10 km (micro scale). This data set provides a unique simultaneous measurement of the wind field and boundary layer structure over large distances and is likely the only one of its kind.