Belay Berhane Demoz

Rotational Raman Lidar measurements of atmospheric temperature in the UV

[1]xa0Measurements of atmospheric temperature have been performed by the NASA Scanning Raman Lidar based on the application of the pure rotational Raman (RR) technique. These measurements represent to our knowledge the first successful lidar measurements of temperature using the RR technique in the UV region, where eye-safe concerns are far less stringent than in the visible and IR. While the system configuration was unoptimized for temperature measurements, nevertheless results were achieved that demonstrate the feasibility of the RR technique for meteorological and climatological applications. Based on 90 minutes data averaging, lidar measurements extend up to 23 km, with RMS deviation between lidar and simultaneous radiosondes not exceeding 1.2 K and average bias smaller than 0.5 K. Simulations reveal that the RR technique in the UV has the potential for providing accurate measurements throughout the troposphere, with appreciable improvement with respect to visible systems for daytime operation.

Raman Lidar Measurements during the International H2O Project. Part I: Instrumentation and Analysis Techniques

The amount of water vapor in the atmosphere helps to determine the likelihood that severe storms may develop. The concentration of water vapor, though, is highly variable in space and time. And yet small changes in water vapor concentration over a short period of time or over a short spatial distance can determine whether a storm may or may not develop. Therefore, in order to improve the ability to forecast severe weather such as thunderstorms it is important to measure water vapor in the atmosphere with high spatial and temporal resolution. One of the most attractive research tools for measuring water vapor in the atmosphere with high spatial and temporal resolution is a Raman lidar. A Raman lidar consists of a laser transmitter, a telescope receiver and optics and electronics for processing opticand electronic signals. A laser pulse is emitted into the atmosphere and it interacts with molecules in the atmosphere causing them to become excited and to emit, through the Raman process, photons of different wavelength than emitted by the laser. The molecule that emitted these emitted. This is the way that a Raman lidar identifies water vapor molecules in the atmosphere. can be identified based on the wavelength of the photons One of the great challenges in Raman lidar measurements has been to make useful daytime measurements of the water vapor profile under bright daytime conditions. In this first of two papers, we describe the instrumentation and analysis of the first documented Raman lidar that is able to measure water vapor in the daytime with sufficient quality to permit the study of developing storm systems.

Characterization of Upper-Troposphere Water Vapor Measurements during AFWEX Using LASE

Water vapor profiles from NASAs Lidar Atmospheric Sensing Experiment (LASE) system acquired during the ARM/FIRE Water Vapor Experiment (AFWEX) are used to characterize upper troposphere (UT) water vapor measured by ground-based Raman lidars, radiosondes, and in situ aircraft sensors. Initial comparisons showed the average Vaisala radiosonde measurements to be 5-15% drier than the average LASE, Raman lidar, and DC-8 in situ diode laser hygrometer measurements. They show that corrections to the Raman lidar and Vaisala measurements significantly reduce these differences. Precipitable water vapor (PWV) derived from the LASE water vapor profiles agrees within 3% on average with PWV derived from the ARM ground-based microwave radiometer (MWR). The agreement among the LASE, Raman lidar, and MWR measurements demonstrates how the LASE measurements can be used to characterize both profile and column water vapor measurements and that ARM Raman lidar, when calibrated using the MWR PWV, can provide accurate UT water vapor measurements.

Raman Lidar Measurements during the International H2O Project. Part II: Case Studies

Abstract The NASA GSFC Scanning Raman Lidar (SRL) participated in the International H2O Project (IHOP) that occurred in May and June 2002 in the midwestern part of the United States. The SRL system configuration and methods of data analysis were described in Part I of this paper. In this second part, comparisons of SRL water vapor measurements and those of Lidar Atmospheric Sensing Experiment (LASE) airborne water vapor lidar and chilled-mirror radiosonde are performed. Two case studies are then presented: one for daytime and one for nighttime. The daytime case study is of a convectively driven boundary layer event and is used to characterize the daytime SRL water vapor random error characteristics. The nighttime case study is of a thunderstorm-generated cirrus cloud case that is studied in its meteorological context. Upper-tropospheric humidification due to precipitation from the cirrus cloud is quantified as is the cirrus cloud optical depth, extinction-to-backscatter ratio, ice water content, cirrus pa...

Rain Evaporation Rate Estimates from Dual-Wavelength Lidar Measurements and Intercomparison against a Model Analytical Solution

AbstractRain evaporation, while significantly contributing to moisture and heat cloud budgets, is a still poorly understood process with few measurements presently available. Multiwavelength lidars, widely employed in aerosols and clouds studies, can also provide useful information on the microphysical characteristics of light precipitation, for example, drizzle and virga. In this paper, lidar measurements of the median volume raindrop diameter and rain evaporation rate profiles are compared with a model analytical solution. The intercomparison reveals good agreement between the model and observations, with a correlation between the profiles up to 65% and a root-mean-square error up to 22% with a 5% bias. Larger discrepancies are due to radiosonde soundings different air masses and model assumptions no more valid along the profile as nonsteady atmosphere and/or appearance of collision–coalescence processes. Nevertheless, this study shares valuable information to better characterize the rain evaporation pr...

Improvement of Raman lidar techniques for quantifying aerosol extinction

The work described here reports on the improvement of a Raman lidar algorithm for measuring aerosol extinction. In order to calculate aerosol extinction from Raman lidar data it is necessary to perform the derivative of a molecular Raman signal with respect to altitude. The typical approach taken in the lidar community is to make an a priori assumption about the functional behavior of the data in order to calculate the derivative. Here a technique is shown that uses the chi-squared test to determine the most likely functional behavior of the data prior to actually calculating the derivative. A mathematical simulation is described that shows the capabilities of this technique and the possibility of reducing the extinction uncertainties with respect to traditional techniques.