S-Pol’s Polarimetric Data Reveal Detailed Storm Features (and Insect Behavior)

Abstract

The National Center for Atmospheric Research (NCAR) operates a state-of-the-art S-band dual-polarization Doppler radar (S-Pol) for the National Science Foundation (NSF). This radar has some similar and some distinguishing characteristics to the National Weather Service (NWS) operational Weather Surveillance Radar-1988 Doppler Polarimetric (WSR-88DP). One key difference is that the WSR-88DP is used for operational purposes where rapid 360° volumetric scanning is required to monitor rapid changes in storm characteristics for nowcasting and issuing severe storm warnings. Since S-Pol is used to support the NSF research community, it usually scans at much slower rates than operational radars. This results in higher resolution and higher data quality suitable for many research studies. An important difference between S-Pol and the WSR-88DP is S-Pol’s ability to use customized scan strategies including scanning on vertical surfaces ([range–height indicators (RHIs)], which are presently not done by WSR-88DPs. RHIs provide high-resolution microphysical structures of convective storms, which are central to many research studies. Another important difference is that the WSR-88DP simultaneously transmits horizontal (H) and vertical (V) polarized pulses. In contrast, S-Pol typically transmits alternating H and V pulses, which results in not only higher data quality for research but also allows for the cross-polar signal to be measured. The cross-polar signal provides estimates of the linear depolarization ratio (LDR) and the co- to cross-correlation coefficient that give additional microphysical information. This paper presents plots and interpretations of high-quality, high-resolution polarimetric data that demonstrate the value of S-Pol’s polarimetric measurements for atmospheric research.

Nocturnal Convection Initiation during PECAN 2015

“…Elevated convergence is associated with weak, persistent mesoscale ascent leading to an elevated layer of enhanced moisture that supports increases in the CAPE and decreases in both the CIN and the LFC height for air parcels originating above the surface. This mesoscale lifting in the environment may combine with stronger and more localized lifting caused by lower-tropospheric gravity waves leading to NCI in this conceptual model (Wilson et al 2018). Banacos and Schultz (2005) and Wilson and Roberts (2006) also noted midlevel convergence and thermodynamic instability as major influences for initiating pristine nocturnal elevated storms during IHOP_2002.…”

“…The OU MAP ensemble had a 50% POD for these events (Table 3). Figure 9 depicts a conceptual model of pristine NCI, following Wilson et al (2018). Elevated convergence is associated with weak, persistent mesoscale ascent leading to an elevated layer of enhanced moisture that supports increases in the CAPE and decreases in both the CIN and the LFC height for air parcels originating above the surface.…”

The ARM Radar Network: At the Leading Edge of Cloud and Precipitation Observations

“…7c and 7d. The Z DR is a measure of the reflectivity-weighted mean axis ratio of the precipitation particle distribution (Hubbert et al 2018). The high positive Z DR values in the lowest 2-3 km indicate the presence of large oblate raindrops and coincide with high positive K DP values that indicate the presence of large liquid water content.…”

“…The high positive Z DR values in the lowest 2-3 km indicate the presence of large oblate raindrops and coincide with high positive K DP values that indicate the presence of large liquid water content. The area of negative K DP values between 6 and 10 km height indicate a zone of ice crystals aligned vertically by an electric field (Hubbert et al 2018).…”

Dual-Polarization Radar Observations of Deep Convection over Lake Victoria Basin in East Africa

“…The Mwanza radar detects this bloom in the form of an expansion in range of widespread, mostly stratiform-type echo in all radial directions from the radar, as can be seen in Figure 6b, near the start of the bloom and in Figure 6c during the bloom. Insects, which typically have elliptically-shaped bodies, with larger horizontal dimensions and smaller vertical extensions, are clearly detectable in the differential reflectivity field (ZDR) [13], with values that can range from 2-7 dB [13], with typical median values of 5-7 dB. The ZDR field in Figure 6d shows that the large expansion of radar echo extending 100 km from the radar at 17:01 is completely due to airborne insects, i.e., all the ZDR values that are not zero Approximately ten hours later, long after the convection has died away and the sun starts to set, a very interesting phenomenon occurs.…”