View source for DPWX/High time resolution observations of a heavy rain area: 3 August 2013

Author: Patrick C. Kennedy


[[Image:3aug2013 overview 360 Z anot.png|300px|right]]
Thunderstorms extending across several Colorado counties as shown by CSU-CHILL reflectivity data collected in a 1.7 deg elevation angle PPI scan on 3 August 2013. High resolution (~1 minute scan interval) time lapse image loops documenting the evolution of the low level reflectivity and radial velocity fields in the echo area immediately southeast of the radar have been assembled.







==Introduction==
Widespread thunderstorm activity developed in the CSU-CHILL coverage area during the afternoon hours of 3 August 2013. Shortly after a thunderstorm passage at the radar site, the scan regime was changed to a continuous series of 360 degree surveillance sweeps at a single elevation angle (1.7 degrees).  The 6 deg per second scan rate provided a new sweep at essentially one minute intervals. This high time resolution made some aspects of the echo system evolution more evident.

==Reflectivity loop==
The following image loop shows the evolution of the reflectivity field at the 1.7 degree elevation during the 2313 - 2355 UTC time period. At the initial time, maximum reflectivities exceeding 60 dBZ were present in the vicinity of the 10 km range ring. This high reflectivity area gradually moved eastward and weakened over the duration of the image loop. A portion of this high reflectivity area affected Weld County station number 340 of the Community Collaborative Rain, Hail and Snow Network [http://www.cocorahs.org CoCoRaHS], marked near the white cross symbol in the images. Differential echo motions produced a counter-clockwise echo circulation pattern in the area located just northwest of station 340.

<center>
<imgloop delay=300 imgprefix="http://www.chill.colostate.edu/anim/3aug2013_hi_res_360/VCHILL/" width=640 height=512>
dBZ.CHL20130803_231254 matro_360 PPI Sweep 01 Plot 0.png
dBZ.CHL20130803_231356 matro_360 PPI Sweep 01 Plot 0.png
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dBZ.CHL20130803_232007 matro_360 PPI Sweep 01 Plot 0.png
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dBZ.CHL20130803_232517 matro_360 PPI Sweep 01 Plot 0.png
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dBZ.CHL20130803_232721 matro_360 PPI Sweep 01 Plot 0.png
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dBZ.CHL20130803_233129 matro_360 PPI Sweep 01 Plot 0.png
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dBZ.CHL20130803_235107 matro_360 PPI Sweep 01 Plot 0.png
dBZ.CHL20130803_235209 matro_360 PPI Sweep 01 Plot 0.png
dBZ.CHL20130803_235311 matro_360 PPI Sweep 01 Plot 0.png
dBZ.CHL20130803_235413 matro_360 PPI Sweep 01 Plot 0.png
dBZ.CHL20130803_235515 matro_360 PPI Sweep 01 Plot 0.png
</imgloop>
</center>

==Radial velocity loop==
The following loop shows the radial velocity patterns recorded during the same time period as the above reflectivity loop. In the begining of the image sequence, a well defined divergence signature was present near the 10 km range ring. (Positive / outbound / purple-yellow colors at greater ranges and negative / inbound / blue-green colors at closer ranges along radials in the southeast azimuth quadrant.) With time, this divergence signature fades as the outflowing cold air pool beneath the weakening thunderstorms became more shallow and subsided below the PPI scan plane. Eventually, the general negative / inbound radial velocities associated with the ambient easterly low level flow become predominant.

<center>
<imgloop delay=300 imgprefix="http://www.chill.colostate.edu/anim/3aug2013_hi_res_360/VCHILL/" width=640 height=512>
Vel.CHL20130803_231254 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_231356 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_231457 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_231559 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_231701 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_231803 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_231905 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_232007 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_232109 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_232211 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_232313 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_232415 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_232517 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_232619 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_232721 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_232823 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_232925 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_233027 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_233129 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_233231 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_233333 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_233435 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_233537 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_233639 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_233741 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_233843 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_233945 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_234047 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_234149 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_234251 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_234353 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_234455 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_234557 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_234659 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_234801 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_234903 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_235005 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_235107 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_235209 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_235311 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_235413 matro_360 PPI Sweep 01 Plot 0.png
Vel.CHL20130803_235515 matro_360 PPI Sweep 01 Plot 0.png
</imgloop>
</center>

==Large specific differential propagation phase magnitudes==
The thunderstorms included in the time lapse loops produced locally heavy rainfall as evidenced by small regions with large positive specific propagation differential phase (<math>K_{dp}</math>) values. Positive <math>K_{dp}</math> develops along radar beam path segments where high concentrations of oblate rain drops exist. <math>K_{dp}</math> is also inversely proportional to the radar wavelength, so <math>K_{dp}</math> will increase as the radar wavelength decreases. This effect can be seen in the final image sequence that was assembled from the 2324 UTC sweep data. The first two plot frames show the echo configuration in terms of the S-Band reflectivity and radial velocity fields respectively. (Use the forward button to advance through the plots.) The second two frames show the S and X-Band <math>K_{dp}</math> fields obtained from the CSU-CHILL's dual frequency configuration. The X-Band <math>K_{dp}</math> magnitudes are nearly 3 times larger than those obtained at S-Band. (Due to differences in the antenna beam pattern widths and range resolutions in the S and X-band channels, the <math>K_{dp}</math> ratio is somewhat less than 3.45 ratio between the CHILL's two specific operating frequencies.) In any event, these large <math>K_{dp}</math> values imply instantenous rainfall rates of ~300 mm / hr. CoCoRaHS staion 340, which did not experience the peak <math>K_{dp}</math> values, reported a 24 hour precipitation total of 0.93 inches (23.6 mm).

<center>
<imgloop delay=300 imgprefix="http://www.chill.colostate.edu/anim/3aug2013_hi_res_360/" width=486 height=453>
1_3aug2013_SZ.png | The 45 and 55 dBZ contours will appear as a reference in all four plots.
2_3aug2013_SV.png | Divergence is associated with the high reflectivity core region.
3_3aug2013_SKdp.png | Maximum S-Band Kdp is between 8 and 10 deg / km
4_3aug2013_XKdp.png | Maximum X-Band Kdp is between 20 and 22 deg / km.
</imgloop>
</center>


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