DUAL-POLARIZATIONRADAR UPGRADE

Emergency Manager WorkshopFeb 5 2013Chad Entremont

WHAT WILL BE COVERED

• What is dual-pol ? Why can we see a larger variety of targets ? • Benefits of detecting different targets–Snow / melting snow /melting layer–Hail cores–Better heavy rain detection–Tornadic debris detection

DIFFERENTIAL REFLECTIVITY (ZDR)

• Definition:  Positive values of ZDR indicate that dominant hydrometeors are larger in the horizontal than in the vertical. Negative values indicate particles are larger in the vertical than the horizontal. Values near zero indicate that hydrometeors are similar in size in the vertical and horizontal.

• Uses:  ZDR can be used to help identify hail shafts, detect updrafts, determine rain drop size, and identify aggregation of dry snow.

CORRELATION COEFFICIENT (CC)

• Definition:  Correlation coefficient provides a measure of the consistency of the shapes and sizes of targets within the radar beam. A higher value shows a higher consistency in the size and shape of radar targets, while a lower value indicates greater variability in shapes and sizes.

• Uses:  CC can be used to help distinguish between meteorological and non-meteorological targets, find the melting layer, identify giant hail, & identify tornadic debris.

CC

KDP is an indication of an increase in the size and concentration of rain drops, and thus, an increase in rain rate.

PRECIP ESTIMATIONS• Dual Pol has shown to offer better precip

estimates (most of the time)• Issues still exist with inaccurate

estimates• Should improve with time

TDS

Hard to detect further away from radar

TDS EXAMPLE 0109Z

• Tornado started• Tight vel couplet

105kts gtg• Nrot 2.0• Potential for a

strong tornado per velocity data

• CC data not indicating any TDS yet

TDS EXAMPLE 0114Z

• TDS! Confirmed Tornado

• CC hole, .45 to .55

• A few ZDR values near Zero

• KEYS!– Collocated with

circ– 45-53 dbz

values

• Intese vel couplet 160kts gtg !!

• Nrot 2.4• Strong Tor very

likely

TRAINING LINKS

http://www.srh.noaa.gov/jan/?n=dualpolupgrade

http://www.wdtb.noaa.gov/courses/dualpol/Outreach/index.html