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Hurricane Karl’s landfall as seen
by high-resolution radar data and WRF
Jennifer DeHart and Robert Houze
Cyclone Workshop10.26.15
NASA grants: NNX13AG71G / NNX12AJ82G
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Karl Best Track and Flights
Image: NHC
Flight
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Rainfall and Mexican Topography
• Intense rainfall collocated with eastern edge of Mexican topography
• Maximum rainfall measured on the northern side of triangular feature
Image: David Roth, NOAA
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Science Questions
• What is the vertical structure of precipitation in Hurricane Karl during landfall over the mountainous terrain of Mexico?
• What can WRF simulations tell us about the underlying processes?
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NASA GRIPDC 8 Flight Track – 09/17/2010
August and September 2010
Key instrument: APR-2 radar on DC8
-10 km flight level-Ku / Ka band-high resolution-downward pointing-cross-track scan
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3-Hour Precip Locations
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Jalapa
Orizaba
?
?
flight
data from NCDC/NHC
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Structure near Jalapa
Minutes after 18 Z
Increased reflectivity intensity near surface
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Upstream Sounding
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10-Minute Precip Locations
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Cordoba
data c/oMichel Rosengaus
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Structure near Orizaba/Cordoba
Minutes after 19 Z
Low-level enhancement not present
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Karl Circulation at 19Z
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A larger view...
Background precipitation important to determining enhancement
Landfall complicates matters by removing energy source
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Cordoba
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0530Z Convection
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OBSERVATIONS SUMMARY• Precipitation values maximize near center of Karl and around topography• compared to other TCs, somewhat
low• Orographic enhancement seen
where positioning is conducive for upslope flow• in Karl, primarily occurs in the low-
levels as a warm-cloud process• Background precipitation important
for final rainfall totals• What can simulations reveal?
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WRF Details
• WRF 3.4.1• Initialized at 00Z on 9/15/2010• 4 domains: 54, 18, 6, 2 km– 6 and 2 km domains follow vortex
• Tested combination of microphysics and boundary layer schemes–WSM, Goddard, Thompson, Morrison,
WDM– YSU, MYJ
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Intensity for MYJ runs
Karl’s intensity is underestimated, but in general schemes do fairly well
Combination of Goddard and MYJ used here, due to ability to reproduce intensity and track
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Observed and Simulated Tracks
Goddard, like other schemes, moves Karl too quickly after 12Z on 9/17, but best follows the observed
track
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Cloud/Rain Mixing Ratios - Goddard
1 km – Hour 66
Increased cloud water concentrations hug line of topography
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Cloud/Rain Mixing Ratios - Goddard
Hour 66
Increased cloud water concentrations top of topographyRain mixing ratios increase towards surface
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CONCLUSIONS• Upslope flow produces enhanced
low-level reflectivity in Karl• cloud water production collected by
falling raindrops• radar doesn’t provide explicit
microphysical or dynamical information
• WRF simulations suggest cloud water production is responsible for enhanced rain
• Future work: WRF simulations with modified topography/land surface
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Jalapa 2
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Orizaba/Cordoba - 2
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SE Reflectivity – Legs 1 and 2
• Echo depth substantially reduced• Small region of intense reflectivity in
eyewall, but convection doesn’t seem as healthy
dBZ
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SE Reflectivity – Legs 3, 4 and 5
dBZ
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Mean Reflectivity - SE
• Decrease in mean reflectivity values with height
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NW Reflectivity
• Strong, continuous reflectivity just past mountain edge along flow
• Convective before mountain
dBZ
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Mean Reflectivity - NW
• Mean reflectivity most intense after passing over highest tops
• Comparable reflectivity strength upstream of mountains compared to other regions of the storm
• Weak mean returns further inland as fall out depletes storm