Radar Scanning IOP for Boundary Layer Clouds

1 November 2013 - 31 October 2017

Lead Scientist: Roger Marchand

Observatory: ENA

Among the motivations for ARM’s development of the W/Ka-band scanning cloud radar (SACR) is to obtain a three-dimensional (3D) description of low-cloud microphysical properties and to study the evolution of the microphysics on sufficiently small time-and-space scales to provide insight on cloud microphysical processes. The current SACR boundary-layer scan mode (known as blrhi), while useful for a variety of purposes, does not meet this objective. The purpose of this proposed IOP is to develop a scanning strategy appropriate for studying small-scale boundary layer cloud 3D structure.
In particular the goal is to scan a small volume with sufficient density that the W/Ka-band reflectivities can be mapped onto a 3D grid with a horizontal and vertical resolution of 50 m or finer. This volume would have a maximum height of about 1.5 km (AGL) and with the target volume lying between 4 and 12 km from the radar. The objectives of this IOP are to: 1) Investigate how large a region can be scanned, when allowing for a maximum scan-time of 1 to 2 minutes.

2) Develop and test software to select the set of azimuth and elevation angles for a target volume at differing ranges to the radar and for clouds with different altitude ranges (nominally between 400 m to 1.5 km). With regard to (1), there is a trade-off between sensitivity and the radar scan rate. The point of this objective is, in a larger sense, to understand quantitatively the trade-off space between sensitivity, scan-resolution, and scan-volume. Depending on the type of boundary layer cloud and processes that will be targeted, it is likely that different configurations may be desired. With regard to (2), the set of azimuth and elevation angles will change with distance to the target and the target elevation. The long-term intent is to be able to track a cloudy volume over time, and a first step in meeting this objective is knowing how to adjust the scan pattern accordingly. It is worth noting that the intent here is to focus on reflectivity measurements. That is, we are more interested in maximizing the reflectivity sensitivity rather than trying to capture Doppler Spectra. Given the large effect that advection and turbulence will have on the Doppler Spectra it is, at-best, unclear that Doppler Spectra measurements would be of much value. Cross-polarization reflectivity measurements, on the other hand, may also prove insightful and will be examined.

Co-Investigators

Nitin Bharadwaj