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M. Weissmann
,
R. Busen
,
A. Dörnbrack
,
S. Rahm
, and
O. Reitebuch

Abstract

This study investigates the possibilities and limitations of airborne Doppler lidar for adaptive observations over the Atlantic Ocean. For the first time, a scanning 2-μm Doppler lidar was applied for targeted measurements during the Atlantic “The Observing System Research and Predictability Experiment” (THORPEX) Regional Campaign (A-TReC) in November and December 2003. The DLR lidar system was operated for 28.5 flight hours, and measured 1612 vertical profiles of wind direction and wind speed with a horizontal and vertical resolution of 5–10 km and 100 m, respectively. On average, there were 25 reliable wind values on every profile, which cover 2500 m in the vertical (about one-third of the mean vertical extent of the profiles). A statistical comparison of 33 dropsondes and collocated lidar winds profiles allowed individual estimates of the standard deviation to be assigned to every wind value and to determine threshold values for an objective quality control of the data. The standard deviation of the difference between dropsonde and lidar winds was correlated with the derived quality indices of the lidar data and was within a range of 0.6–1.8 m s−1. Comparisons of the lidar data to the operational analysis revealed differences of up to ±15 m s−1. This emphasizes the need for more representative and higher resolved wind measurements in data-sparse regions above the Atlantic Ocean. The study constitutes the basis for the assimilation of the lidar data and impact studies at the European Centre for Medium-Range Weather Forecasts (ECMWF).

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J. Ström
,
R. Busen
,
M. Quante
,
B. Guillemet
,
P. R. A. Brown
, and
J. Heintzenberg

Abstract

During the pre-EUCREX (European Cloud and Radiation Experiment) intercomparison of airborne instrumentation in January 1992, nine hygrometers mounted on three different aircraft were compared. Although the different instruments are based on completely different principles and the three aircraft have very different flying characteristics, humidity data from both vertical profiles as well as horizontal flight legs showed good agreement. Despite the different aircraft limitations the intercomparison was done with the aircraft in close formation. In terms of relative difference in mixing ratio, most instruments agreed to within ±5% for values down to about 0.1 g kg−1. For mixing ratios between 0.03 and 0.1 g kg−1 most instruments agreed to within ±15%. Systematic differences between the instruments suggest that in joint experiments where data will be shared, the same algorithms for evaluating and converting humidity parameters should be used whenever possible.

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