Saggy Bright Bands

Kumjian, M., Pennsylvania State University

Cloud Processes

Convective Processes

Kumjian MR, S Mishra, SE Giangrande, T Toto, AV Ryzhkov, and A Bansemer. 2016. "Polarimetric radar and aircraft observations of saggy bright bands during MC3E." Journal of Geophysical Research: Atmospheres, 121(7), 10.1002/2015jd024446.


Time series of quasi-vertical profiles from 27 April 2011, 05:00 UTC through about 15:00 UTC. Data were collected using the CSAPR at the ARM Southern Great Plains site during MC3E. Radar variables shown are (a) reflectivity factor, (b) differential reflectivity, (c) differential phase shift, and (d) co-polar correlation coefficient. The white bar indicates missing data. The bright band is at 2 km height at the beginning of the period. Notice the transient sagging of the bright band.


Citation aircraft-mounted Cloud Imaging Probe images from 0943 UTC on 27 April 2011. The particles were sampled at about -4 degrees C. Each panel corresponds to one second of data. The height of each panel represents 1.6 mm. Notice the large number of needle-like ice crystals and roundish, rimed particles. These particles suggest rime splintering.


Time series of quasi-vertical profiles from 27 April 2011, 05:00 UTC through about 15:00 UTC. Data were collected using the CSAPR at the ARM Southern Great Plains site during MC3E. Radar variables shown are (a) reflectivity factor, (b) differential reflectivity, (c) differential phase shift, and (d) co-polar correlation coefficient. The white bar indicates missing data. The bright band is at 2 km height at the beginning of the period. Notice the transient sagging of the bright band.

Citation aircraft-mounted Cloud Imaging Probe images from 0943 UTC on 27 April 2011. The particles were sampled at about -4 degrees C. Each panel corresponds to one second of data. The height of each panel represents 1.6 mm. Notice the large number of needle-like ice crystals and roundish, rimed particles. These particles suggest rime splintering.

Science

A new technique for viewing radar observations allows for analyzing the evolution of the melting layer “bright band,” a signature associated with melting snowflakes. Radar and aircraft data demonstrate that transient bright band sagging provides information about the ice particles falling into the layer from above.

Impact

Bright band sagging is associated with fast-falling, denser particles entering the melting layer. In some cases, this is related to heavy riming, indirectly indicating the presence of supercooled liquid water.

Summary

Combined dual-polarization radar and aircraft observations from the Midlatitude Continental Convective Clouds Experiment (MC3E) are used to investigate the melting layer in stratiform precipitation. A new radar technique is applied that provides time-height depictions of bright band evolution. Transient bright band sagging is found to occur when denser hydrometeors fall into the melting layer from above. In one case, the particle densification is caused by riming, as evidenced by supercooled liquid water detection and large quantities of needle-like ice crystals thought to be formed by rime splintering (secondary ice production). A simplified bin microphysical model is used to reproduce the signature, showing that increased particle fall speeds are the primary driver of bright band sagging, with increased precipitation intensity as a secondary factor. Scanning dual-polarization radar observations are capable of detecting these processes, potentially allowing for real-time detection of in-cloud icing conditions.