Three-Dimensional Precipitation Structure of Tropical Cyclones AMS Hurricane and Tropical Meteorology Conference May 2nd, 2008 Deanna A. Hence and Robert A. Houze, Jr. University of Washington Willoughby (1988) What is the typical vertical structure of these mesoscale features?

Idealized vertical structures suggested by past studies Inner rainband Outer rainband Inner rainband Deep Restricted

Objectives of this study Determine statistically the vertical structures of the mesoscale precipitation features of hurricanes Determine how these structures vary from eyewall to inner rainband to outer rainband regions

TRMM Precipitation Radar (PR) 13.8 GHz (2.17 cm) radar 17º (from nadir) scanning angle 215 km swath width 4.3 km horizontal resolution 250 m vertical resolution From NASA TRMM website (

Annuli and Quadrant Analysis Center location, eye diameter and storm motion provided in the National Hurricane Center (NHC) best track data

Primary Analysis Tools Contoured Frequency by Altitude Diagrams (CFADS, Yuter and Houze 1995) NCAR Zebra software Relative frequency of occurrence

Ordinary Deep Convection CFAD Convective component Stratiform component Total

Analyze CFADs of all overpasses of hurricanes that reached Category 4 or 5. Atlantic/Gulf of Mexico/Caribbean basin storms from Determine how structures of eyewall, rainbands, and outer bands vary with radius and storm quadrant Vertical Structure Analysis with CFADS

CFADS by Annulus-Outer Region Resembles ordinary buoyant convection –Broad distribution of reflectivities below melting level –Bright band signature –Relatively broad distribution above melting level reaching to 11 km Outer Region Annulus 5

CFADS by Annulus -- Rainband Region Strong brightband signature Sharp dropoff of reflectivity above melting level reaching to just below 10 km But… Narrower distribution of reflectivity below melting level…not like ordinary convection Looks more like an eyewall CFAD Rainbands Annulus 3

CFADs by Annulus– Eyewall Region Relatively narrow but intense distribution below melting level Weak if any brightband signature Mostly narrow & sharp distribution above melting level Outliers suggest occasional intense convective towers reaching over 12 km Not like convective or stratiform CFADs of ordinary convection Eyewall Annulus 1

Eyewall CFADs by Quadrant — All Overpasses Storm motion Quad 1Quad 4 Quad 2Quad 3 LF Quad 1 RF Quad 4 RR Quad 3 LR Quad 2

Rainbands CFADs by Quadrant — All Overpasses Storm motion RF Quad 4 RR Quad 3 LR Quad 2 LF Quad 1

Conclusions Outer region CFADs –convective-like distribution Rainband CFADs –Vertically limited –Narrow distribution –CFADs similar in all quadrants Eyewall CFADs –Deep –Intense reflectivities –Relatively narrow distribution with extreme outliers –Right side stronger than left side

Ongoing and Future Work Continue expansion of database to all Atlantic Basin hurricanes, and eventually to all basins Stratify overpasses based on intensity, track speed, wind shear, sea surface temperature, and other factors known to influence storm structure and intensity Perform EOF analysis to objectively sort CFADs Use technique to analyze model simulations

Eyewall and Secondary Eyewall Structure Secondary eyewall is similar to primary except not as deep (Houze et al. 2007) From Houze et al. (2007)

Outer Rainbands Similar to marine convection found over tropical oceans (e.g. Molinari et al. 1999, Cecil et al. 2002) Found on boundary between the tropical cyclone circulation and the environment (Willoughby et al. 1984) From Molinari et al. (1999)

Rainband Characteristics Contain stratiform precipitation with some embedded convection, tend to be more cellular than the eyewall (e.g. Barnes et al. 1983, Willoughby et al. 1984) May form because of propagating vortex Rossby waves (e.g. Montgomery and Kallenbach 1997, Corbosiero et al. 2006) From Hence and Houze (2008)