High Rain Rates at Denver International Airport Observed with Indexed Beams: Difference between revisions

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On 10 September 2006, the CSU-CHILL radar made continuous 0.5 deg
On 10 September 2006, the CSU-CHILL radar made continuous 0.5 deg elevation PPI scans in alternating VH polarization mode.  In these scans, the beam revisited a given location at essentially one minute intervals.  While this scanning procedure was in use, heavy thunderstorm precipitation developed around Denver International Airport.  To provide geographic references for the radar data, the FAA airport taxi diagram for KDEN is shown below.  A red dot has been added to indicate the approximate location of the ASOS sensors
elevation PPI scans in alternating VH polarization mode.  In these scans,
where the basic elements of the surface weather reports (METARS) are measured. A horizontal size scale can be obtained from the runway length depictions; runway 35L / 17R (immediately to the west of the ASOS dot) is 3.66 km (12,000 ft) long.)
the beam revisited a given location at essentially one minute
 
intervals.  While this scanning procedure was in use, heavy
thunderstorm precipitation developed around Denver International
Airport.  To provide geographic references for the radar data,
the FAA airport taxi diagram for KDEN is shown below.  A red dot
has been added to indicate the approximate location of the ASOS sensors
where the basic elements of the surface weather reports (METARS)are measured.
A horizontal size scale can be obtained from the runway length depictions;
runway 35L / 17R (immediately to the west of the ASOS dot) is 3.66 km
(12,000 ft) long.)
<math>Insert formula here</math>
<math>Insert formula here</math>
[[Image:KDEN_taxi_chart.png]]


For each PPI scan, the one-way specific propagation differential phase (Kdp
[[Image:KDEN_taxi_chart.png|600px]]
in degrees per km) was calculated using the methods of Cifelli et. al
 
(''J. Geophys. Res''.; 2002).  Kdp-based rain rates were then provided by
For each PPI scan, the one-way specific propagation differential phase (<math>K_{dp}</math> in degrees per km) was calculated using the methods in <ref name="cifelli">[http://www.agu.org/journals/jd/jd0218/2000JD000264/ Cifelli et. al, ''J. Geophys. Res., 2002'']</ref>. <math>K_{dp}</math>-based rain rates were then provided by <math>R = 40.5 * K_{dp} ^{0.85}</math>, from Eq 8.14 in <ref name="bc">Bringi and Chandrasekar, ''Polarimetric Doppler Weather Radar: Principles and Applications'', (2001)</ref>.
R = (40.5 * (Kdp**.85)) from Eq 8.14 in the text of Bringi and Chandrasekar (2001).
In the time lapse sequence shown below, these rain rates have been color
In the time lapse sequence shown below, these rain rates have been color
coded as follows:
coded as follows:


<center>
{| {{Prettytable}}
{| {{Prettytable}}
!{{Hl3}} | Rain Rate
!{{Hl3}} | Rain Rate<br>(mm/hr)
!{{Hl3}} | Color Codes
!{{Hl3}} | Color Codes
|-
|-
|25 mm / hr
|25
|light blue
|light blue
|-
|-
|50 mm / hr
|50
|light red
|light red
|-
|-
|75 mm / hr
|75
|green
|green
|-
|-
|100 mm / hr
|100
|blue
|blue
|-
|-
|125 mm / hr
|125
|yellow
|yellow
|-
|-
|150 mm / hr
|150
|dark red
|dark red
|-
|-
|175 mm / hr
|175
|grey
|grey
|}
|}
</center>


(Note: PPI times (UTC) appear in the lower left quadrant of each image).
(Note: PPI times (UTC) appear in the lower left quadrant of each image).
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[[Image:10sept06_KDEN_KDP_loop_ver_1.gif]]
[[Image:10sept06_KDEN_KDP_loop_ver_1.gif]]


The patterns evident in the time lapse sequence demonstrate the small time and space scales on which thunderstorm precipitation evolves.  The METAR prevailing visibility decreased to 0.25 statute miles in heavy rain at 2342 UTC. The CSU-CHILL data indicate that even higher rain rates existed over runway 35R - 17L, while rainfall rates never reached 25 mm per hour over the approach end of runway 7 in the western portion of the airport.  Since the radar data were collected in indexed beam mode, the range gate azimuths remained constant.  These indexed beams improve the frame-to-frame stability in the time lapse sequence.


The patterns evident in the time lapse sequence demonstrate the small time
==References==
and space scales on which thunderstorm precipitation evolves.  The METAR
<references/>
prevailing visibility decreased to 0.25 statute miles in heavy rain at 2342UTC.
The CSU-CHILL data indicate that even higher rain rates existed over runway
35R - 17L, while rainfall rates never reached 25 mm per hour over the approach end of runway 7 in the western
portion of the airport.  Since the radar data were collected in indexed beam mode,
the range gate azimuths remained constant.  These indexed beams improve the
frame-to-frame stability in the time lapse sequence.

Revision as of 12:27, 17 June 2007

On 10 September 2006, the CSU-CHILL radar made continuous 0.5 deg elevation PPI scans in alternating VH polarization mode. In these scans, the beam revisited a given location at essentially one minute intervals. While this scanning procedure was in use, heavy thunderstorm precipitation developed around Denver International Airport. To provide geographic references for the radar data, the FAA airport taxi diagram for KDEN is shown below. A red dot has been added to indicate the approximate location of the ASOS sensors where the basic elements of the surface weather reports (METARS) are measured. A horizontal size scale can be obtained from the runway length depictions; runway 35L / 17R (immediately to the west of the ASOS dot) is 3.66 km (12,000 ft) long.)

For each PPI scan, the one-way specific propagation differential phase ( in degrees per km) was calculated using the methods in [1]. -based rain rates were then provided by , from Eq 8.14 in [2]. In the time lapse sequence shown below, these rain rates have been color coded as follows:

Rain Rate
(mm/hr) 		Color Codes
25 light blue
50 light red
75 green
100 blue
125 yellow
150 dark red
175 grey

(Note: PPI times (UTC) appear in the lower left quadrant of each image).

The patterns evident in the time lapse sequence demonstrate the small time and space scales on which thunderstorm precipitation evolves. The METAR prevailing visibility decreased to 0.25 statute miles in heavy rain at 2342 UTC. The CSU-CHILL data indicate that even higher rain rates existed over runway 35R - 17L, while rainfall rates never reached 25 mm per hour over the approach end of runway 7 in the western portion of the airport. Since the radar data were collected in indexed beam mode, the range gate azimuths remained constant. These indexed beams improve the frame-to-frame stability in the time lapse sequence.

References

  1. ↑ Cifelli et. al, J. Geophys. Res., 2002
  2. ↑ Bringi and Chandrasekar, Polarimetric Doppler Weather Radar: Principles and Applications, (2001)
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