1. Vertical Distribution of Radar Reflectivity in Hurricanes in the Presence of Shear
Jennifer C. DeHart, Robert A. Houze, Jr. and Deanna A. Hence
University of Washington
AMS Tropical Conference –
Image: NASA

2. UL DL UR DR Black et al., 2002 modified by Houze 2009
Shear from directions.
Updrafts initiate and are advected cyclonically around the eye
Z decreases around from freezing and fallout
Ice vs heavy particles
Trans: Black qualitative, want quantitative
Can have single cells or clusters
Mature 90deg to left and then develop DD UR DR
Black et al., 2002 modified by Houze 2009

3. Quantifying Vertical Structure
Hence and Houze 2011, 2012 (a,b) analyzed data from TRMM PR
Snapshots of radar reflectivity
10+ years of data
Contoured by Frequency Altitude Diagrams (CFADs)
hPa shear from NCEP
Then explain CFADs in next slide
Trans: CFADs, an example in next slide

4. Height (km) Reflectivity (dBZ) Hence and Houze 2011
Joint probability distribution, frequency with which pixel is at a certain level and dBZ. Normalized by max frequency.
Contains storms of all intensities and only their EWs.
Strong upper level weak reflectivities, broad distribution at lower levels, but modal distribution includes strong convective echoes.
Slantwise structure appears, but also see very strong and very deep echoes, corresponding to asymmetric convective cells. (outliers)
Trans: don’t just want to see total structure, does it vary? Separated data into shear quadrants
Reflectivity (dBZ)
Hence and Houze 2011

5. Upper level weak reflectivities, modal distribution extends to low levels.
Higher prob of having full, intense Z field in DL.
UR looks to be weakest, but there is substantial variability.
Lack of low refl in DR -> strong cores, lack of light rain
TRANS: differences can be better shown through use of anomalies.
Hence and Houze 2011

6. DL DR 8 Shear 6 2 Height (km) UL UR 8 6 2 30 40 30 40
Describe convection in shear quadrants.
TRANS: have this for statistics, but what about actual storms where we have more days of sampling and potentially velocity? 6 2 30 40 30 40
Courtesy of D. Hence
Reflectivity (dBZ)

7. Field Campaigns RAINEX (2005) IFEX/GRIP (2010) Katrina: 8/28 NOAA 43
Earl: 8/29, 8/30, 9/1, 9/2
NOAA 42 & 43
Katrina on this day was category 5. sampled from 17-23Z.
Earl started out as a cat 2 and reached cat 4 during the second set of flights.
Shear for katrina and earl was fairly comparable on these days: around 4 m/s.
Earl was also intense on the 1st, but shear was roughly double (10 m/s)
Looking at qualitative similarities as there are some differences between the datasets. Currently talking with people to work with this issue.
TRANS: katrina

8. Hurricane Katrina – 8/28/2005
Strong upper level signal for small droplets, ice particles for lower reflectivities. Low level modal distribution centered around higher reflectivities.
Overall, lower level reflectivity signature is narrower than statistics, possibly due to cat 5 status of katrina at time of data collection. Shear also weaker.
TRANS: again, want to look at shear quadrant analysis

9. Shear Again, strong signal of upper level ice and small droplets and .
See shift in DR reflectivities to stronger echoes.
Also see spread DL, though more blocky, concentrated at high reflectivities and lower ones.
Upshear, modal distribution much smaller and more peaked. Less variability.
Modal distributions of upshear quadrants also on high end compared with deannas. Again, probably related to strong intensity and/or weak shear.
TRANS: anomalies give a better sense of this.

10. Shear Downshear-upshear differences dominate the anomalies.
Upshear have much weaker probabilities overall.
Much more dominant than in the statistics given.
TRANS: what about earl?

11. Hurricane Earl – 8/30/2010 Again upper level signature.
Low-level modal distribution doesn’t include higher reflectivities, but distribution is quite broad and spans nearly 20 dB at stronger returns.
TRANS: split by shear

12. Shear Similar story for earl on 8/30.
Difference between downshear and upshear isn’t as strong.

13. Hurricane Earl – 8/30/2010

14. Shear Very different from other structures.
Same as mean DR, stronger than mean DL and UL.

15. Conclusions
Structures of Katrina and Earl at strong intensities share similarities with statistics
Intense low-level reflectivities
Early sampling of Earl on 8/30 did not
Shear calculation issue?
Rapid Intensification?
Circulation pattern?

16. End This research was supported by NSF grant # ATM-0743180 and NASA grant #NNX09AM73G