Retrievals of ice cloud microphysical properties of deep convective systems using radar measurements

Abstract

This study presents newly developed algorithms for retrieving ice cloud microphysical properties (ice water content (IWC) and median mass diameter (D m )) for the stratiform rain and thick anvil regions of deep convective systems (DCSs) using Next Generation Radar (NEXRAD) reflectivity and empirical relationships from aircraft in situ measurements. A typical DCS case (20 May 2011) during the Midlatitude Continental Convective Clouds Experiment (MC3E) is selected as an example to demonstrate the 4-D retrievals. The vertical distributions of retrieved IWC are compared with previous studies and cloud-resolving model simulations. The statistics from six selected cases during MC3E show that the aircraft in situ derived IWC and D m are 0.47 ± 0.29 g m À3 and 2.02 ± 1.3 mm, while the mean values of retrievals have a positive bias of 0.19 g m À3 (40%) and negative bias of 0.41 mm (20%), respectively. To evaluate the new retrieval algorithms, IWC and D m are retrieved for other DCSs observed during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX) using NEXRAD reflectivity and compared with aircraft in situ measurements. During BAMEX, a total of 63, 1 min collocated aircraft and radar samples are available for comparisons, and the averages of radar retrieved and aircraft in situ measured IWC values are 1.52 g m À3 and 1.25 g m À3 with a correlation of 0.55, and their averaged D m values are 2.08 and 1.77 mm. In general, the new retrieval algorithms are suitable for continental DCSs during BAMEX, especially within stratiform rain and thick anvil regions.

Understanding Ice Cloud‐Precipitation Properties of Three Modes of Mesoscale Convective Systems During PECAN

“…This is not true for the IWC retrievals using K dp (Aydin & Tang, ; Lu et al, ; Ryzhkov & Zrnic, ). Here the IWCs and IWPs retrieved from two algorithms (Lu et al, ; Tian et al, ) are compared for the PS case in order to help quantify the uncertainties of the Z e retrievals.…”

“…It was further evaluated with aircraft‐measured IWC values from two field campaigns, the Mid‐latitude Continental Convective Clouds Experiment (MC3E) and the Bow Echo and Mesoscale Convective Vortices Experiment (BAMEX). Compared with the aircraft in situ measurements, the uncertainty of IWC retrievals is ~40% during the MC3E, while a positive bias is found during the BAMEX around 30% (Tian et al, ). The retrieval algorithms are capable of characterizing IWCs over the SR regions of midlatitude continental convective systems.…”

Comparisons of Ice Water Path in Deep Convective Systems Among Ground‐Based, GOES, and CERES‐MODIS Retrievals

“…To determine the possible reasons for the retrieval differences and their low correlation, the uncertainty of NEXRAD retrievals is analyzed first. Tian et al () found that the NEXRAD‐retrieved IWC is 20% larger than the aircraft in situ measurements; thus, it is highly probable that the NEXRAD IWPs will be roughly 20% larger than the “true” IWPs, if the in situ measurements are treated as “ground‐truth.” As mentioned in section 2.1, supercooled liquid water was observed by aircraft probes during MC3E around the −30°C level, similar to previous reports (Rosenfeld & Woodley, ). Those large amounts of supercooled liquid water may enhance NEXRAD radar reflectivity measurements and therefore result in larger IWC retrievals and overestimation of IWPs.…”

“…However, a significant amount of supercooled liquid water was observed by aircraft probes above 4 km (see Figure 2 in Wang et al, , for reference). IWC retrievals using measured radar reflectivity for ice cloud with contamination of supercooled liquid water can result in relatively large uncertainties near the melting band (Tian et al, ). Thus, in this study, IWP is calculated by integrating NEXRAD‐estimated IWC profile from 5 km to cloud top (NEXRAD radar echo top).…”

“…As the cloud optical depth increases beyond the relevant range, the retrieved effective size becomes less and less representative for the entire cloud (Dong et al, ; Zhang & Platnick, ). Also, in general, ice particle sizes in the upper layers normally increase from the top downward (Field et al, ; Heymsfield et al, ; Tian et al, ; van Diedenhoven et al, ; Wang et al, ). This height dependence introduces a bias in the satellite‐retrieved IWPs.…”