Ceilometer-Based Rain-Rate Estimation: A Case-Study Comparison With S-Band Radar and Disdrometer Retrievals in the Context of VORTEX-SE

Abstract

Attenuated backscatter measurements from a Vaisala CL31 ceilometer and a modified form of the wellknown slope method are used to derive the ceilometer extinction profiles during rain events, restricted to rainfall rates (RRs) below approximately 10 mm/h. RR estimates from collocated S-band radar and portable disdrometer are used to derive the RR-to-extinction correlation models for the ceilometer-radar and ceilometer-disdrometer combinations. Data were collected during an intensive observation period of the Verification of the Origins of Rotation in Tornadoes Experiment Southeast (VORTEX-SE) conducted in northern Alabama. These models are used to estimate the RR from the ceilometer observations in similar situations that do not have collocated radar or the disdrometer. Such correlation models are, however, limited by the different temporal and spatial resolutions of the measured variables, measurement capabilities of the instruments, and the inherent assumption of a homogeneous atmosphere. An empirical method based on extinction and RR uncertainty scoring and covariance fitting are proposed to solve, in part, these limitations.

Motivating a Synergistic Mixing-Layer Height Retrieval Method Using Backscatter Lidar Returns and Microwave-Radiometer Temperature Observations

“…Gross outliers are defined as biased estimates (M LH X -M LH RS , X=SYN, EKF, MWR, DWL) above ±1σ of the mean of the associated MLH bias histogram computed hourly. To further improve the significance of results, gross outliers were removed prior to evaluating correlation statistics via a similar procedure as that described in [18] and [60]. When Fig.…”

Numerical Solver for Vertical Air Motion Estimation

“…This system measures the volume reflectivity spectral density (with respect to velocity), η(v), with averaged spatial and temporal resolutions of 5 m and 16 s, respectively. From these it is possible to obtain profiles of the spectral reflectivity factor, Z(v), vertical velocity, v, and spectrum width, w. This radar enables to study the atmospheric boundary layer behaviour as well as precipitation events, because it is able to detect both clear-air echo and precipitation [5].…”

“…Data products.-The steps to estimate the RR and DSD from radar measurements begin with the measured radar volume reflectivity η(v) as a function of velocity (see details in Appendix of [5] and physical basis in [9]). The DSD is defined as…”

“…RR estimation is influenced by the assumed DSD. In turn, the DSD can be computed from the vertically pointed radar Doppler spectrum with the assumption that the drops are Rayleigh scatterers falling at their terminal velocities [5]. However, in practice, the Doppler spectrum is affected by the ambient vertical air motion (VAM).…”

“…In contrast, this paper tackles VAM estimation relying on RR measurements by a ground-based disdrometer, assuming high RR correlation between different measurement heights considering 5-min average ensembles. Although collision and coallescence processes limit radar-and disdrometer-DSD coincidence, correlation coefficients of ρ 0.75 are found for the RR between disdrometer and radar at 500 m in [5]. This paper is organised as follows: Sect.…”