Ground-Based DWL Laboratory: Cirrus Studies

SWA processed single shot and poly-pulse scanning data for July 10, 1992, 1623Z, which had a high thin cirrus cloud present. Each data set was noise filtered and least squares fit to a sine wave to establish "ground truth" winds. Using the FORTRAN sine fitting model, SWA generated sine fits for a series of range gates going from a strong SNR region to a weak SNR region for both unfiltered and filtered data. At range gate 5, the signal-to-noise (SNR) was very low. At range gates 6-15 there were strong signals to make LOS estimates. However, at range gate 16, the single shot data showed loss of signal where the poly-pulse data (50 shot averages) was able to make a LOS measurement. Only noise was found from range gates 17-29. The cirrus cloud provided signal at range gates 30-32.

SWA selected the MSFC cirrus cloud data sets from July 17, 1992, 1623Z, to look at a time series of four sequential VADS;

D13 D14 D15 D16.

The lidar wind information from the cirrus clouds appears to be very variable. A longer time series of lidar data is needed to examine this closer.

On May 28, 1993, the MSFC lidar was held in a fixed scan with an elevation angle at near zenith. At around 10 km, a thin cirrus deck was reported. The following figures depict the poly-pulse lidar wind velocities and amplitudes for 400 seconds.

• Unfiltered poly-pulse ground-based Doppler lidar lidar wind velocities as a function of range and time. The data was taken at 11:27:44 for 5/28/93 with an elevation angle at near zenith. Cirrus cloud returns are shown at range gates 33-38.

• Unfiltered poly-pulse ground-based Doppler lidar amplitudes as a function of range and time. The data was taken at 11:27:44 for 5/28/93 with an elevation angle at near zenith. Cirrus cloud returns are shown at range gates 33-38.

• Unfiltered poly-pulse ground-based Doppler lidar lidar wind velocities as a function of range and time. The data was taken at 11:29:24 for 5/28/93 with an elevation angle at near zenith. Cirrus cloud returns are shown at range gates 33-38.

• Unfiltered poly-pulse ground-based Doppler lidar amplitudes as a function of range and time. The data was taken at 11:29:24 for 5/28/93 with an elevation angle at near zenith. Cirrus cloud returns are shown at range gates 33-38.

• Unfiltered poly-pulse ground-based Doppler lidar lidar wind velocities as a function of range and time. The data was taken at 11:31:04 for 5/28/93 with an elevation angle at near zenith. Cirrus cloud returns are shown at range gates 33-38.

• Unfiltered poly-pulse ground-based Doppler lidar amplitudes as a function of range and time. The data was taken at 11:31:04 for 5/28/93 with an elevation angle at near zenith. Cirrus cloud returns are shown at range gates 33-38.

• Unfiltered poly-pulse ground-based Doppler lidar lidar wind velocities as a function of range and time. The data was taken at 11:32:44 for 5/28/93 with an elevation angle at near zenith. Cirrus cloud returns are shown at range gates 33-38.

• Unfiltered poly-pulse ground-based Doppler lidar amplitudes as a function of range and time. The data was taken at 11:32:44 for 5/28/93 with an elevation angle at near zenith. Cirrus cloud returns are shown at range gates 33-38.

As seen in Figs. D.23 and D.24, the cirrus return ends at around 370 seconds. The detection of the cirrus deck is highlighted by a time series of the amplitude and wind velocity at range gate 36.

On October 10, 1992, the lidar was pointing straight up in a non-scanning mode at a thin cirrus deck. A range versus time wind velocity plot shows the cirrus deck at around the 41st range gate. Vertical wind speeds as a function of range gate were examined around the cirrus deck. For comparison, the vertical wind speeds for the mid-troposphere (strong SNR to weak SNR) are shown. The variance found in the mid-troposphere was approximately half that found in the cirrus layer.