Principal Rainband of Hurricane Katrina as observed in RAINEX Anthony C. Didlake, Jr. 28 th Conference on Hurricanes and Tropical Meteorology April 29, 2008 Willoughby 1988

Barnes et al Low-level radial inflow overturns inside of leaning reflectivity tower Low-level radial inflow overturns inside of leaning reflectivity tower Downdraft within reflectivity tower continues as radial inflow Downdraft within reflectivity tower continues as radial inflow Cross-band structure

Hurricane Katrina (2005) ELDORA radar Sampling resolution ~0.4 kmSampling resolution ~0.4 km

Similarities to Barnes et al Hence and Houze 2008

Inner-edge downdraft What causes it? What causes it? How often does it occur? How often does it occur? What are the effects of it? What are the effects of it?

Convective/stratiform classification Convective Stratiform Weak echo No echo Similar to Steiner et al. 1995, TRMM satellite data classification Similar to Steiner et al. 1995, TRMM satellite data classification

Radial cross sections at regular angular intervals Radial cross sections at regular angular intervals 0.375°  109 cross sections0.375°  109 cross sections Cross section coordinates based on classification Cross section coordinates based on classification Rainband cross sections

dBZ

Updrafts are strong and broad Updrafts are strong and broad Two downdraft regimes Two downdraft regimes Inner-edge downdrafts are slightly weaker and more localized Inner-edge downdrafts are slightly weaker and more localized

Vertical velocity (m/s) (plan view)

Buoyant air parcel dBZ

Conclusions Overturning updraft, low-level downdraft, inner-edge downdraft Overturning updraft, low-level downdraft, inner-edge downdraft Inner-edge downdraft: Inner-edge downdraft: Convective scale feature, ~5 kmConvective scale feature, ~5 km Creates sharp reflectivity gradientCreates sharp reflectivity gradient Forced by rainband updrafts?Forced by rainband updrafts?

Questions?

Buoyancy pressure-gradient acceleration field H L Buoyant air parcel

Idealized structure of a tropical cyclone Primary and Secondary eyewalls Primary and Secondary eyewalls Stationary Band Complex (SBC) Stationary Band Complex (SBC) principal bandprincipal band secondary bandsecondary band Willoughby 1988 upwind downwind

B A D C Autocorrelation along rainband

Strong inner-edge downdrafts

Low-level tangential wind max on inner-side of rainband

References Willoughby, H.E., 1988: The dynamics of the tropical cyclone core. Aust. Met. Mag., 36, Willoughby, H.E., 1988: The dynamics of the tropical cyclone core. Aust. Met. Mag., 36, Barnes, G.M., E.J. Zipser, D. Jorgensen, and F. Marks, Jr., 1983: Mesoscale and convective structure of a hurricane rainband. J. Atmos. Sci., 40, Barnes, G.M., E.J. Zipser, D. Jorgensen, and F. Marks, Jr., 1983: Mesoscale and convective structure of a hurricane rainband. J. Atmos. Sci., 40, Hence, D.A. and R.A. Houze, Jr., 2008: Kinematic structure of convective-scale rainband features in Hurricanes Katrina and Rita (2005). J. Geophys. Res., accepted. Hence, D.A. and R.A. Houze, Jr., 2008: Kinematic structure of convective-scale rainband features in Hurricanes Katrina and Rita (2005). J. Geophys. Res., accepted.

“Strong” inner-edge downdrafts occur less frequently than “strong” updrafts “Strong” inner-edge downdrafts occur less frequently than “strong” updrafts Inner-edge downdrafts occur right along the reflectivity gradient Inner-edge downdrafts occur right along the reflectivity gradient

Convective/stratiform classification Technique used in Steiner et al. 1995, Yuter and Houze 1997, Yuter et al Technique used in Steiner et al. 1995, Yuter and Houze 1997, Yuter et al Algorithm separates convective regions from stratiform regions by comparing local reflectivity to background reflectivity Algorithm separates convective regions from stratiform regions by comparing local reflectivity to background reflectivity Tuning of algorithm required to recognize convective regions; the rest is designated as stratiform Tuning of algorithm required to recognize convective regions; the rest is designated as stratiform

Classification Algorithm Convective center if: Convective center if: Z  Z tiZ  Z ti Z-Z bg  Z cc (Z bg )Z-Z bg  Z cc (Z bg ) Classified convective within R(Z bg ) from convective center, remaining is classified stratiform (unless Z < Z we ) Classified convective within R(Z bg ) from convective center, remaining is classified stratiform (unless Z < Z we ) Z cc Z bg Z ti = 45 dbZ Z we = 20 dbZ R = (Z bg -20) R bg = 11 km a=9, b=45

Statistics of reflectivity data 2D frequency distributions (in % of height total) Convective pixels Stratiform pixels Convective pixels Stratiform pixels Height (km) dBZ dBZ Yuter and Houze 1995

Beyond Barnes et al. (1983) K1 x Deanna Hence

Strong downdrafts where horizontal velocity decreases with height

Tilting of vorticity tubes creates negative vertical vorticity

Negative vertical vorticity is stretched in region of convergence and advected downward. It is confined to the lower layers by divergence at the ocean surface.

Strong lower-level vertical vorticity is manifested in a local tangential wind maximum

Future work Explore the roll of fluctuating updrafts and downdrafts in strength of storm circulation Explore the roll of fluctuating updrafts and downdrafts in strength of storm circulation Compare dynamics with other convective regimes: eyewall, secondary eyewall, outer rainbands Compare dynamics with other convective regimes: eyewall, secondary eyewall, outer rainbands Analyze more ELDORA data volumes, N43 data, Rita rainbands Analyze more ELDORA data volumes, N43 data, Rita rainbands Compare observations with model simulations, analyze evolution of rainbands Compare observations with model simulations, analyze evolution of rainbands

Average tangential wind (m/s) distance (km) altitude (km)

Aircraft and instruments US Naval Research Laboratory P3 (NRL) US Naval Research Laboratory P3 (NRL) ELDORA radar ELDORA radar Sampling resolution ~0.4 kmSampling resolution ~0.4 km NOAA P3 (N42, N43) NOAA P3 (N42, N43) Dropsondes and Doppler radar (dual-Doppler analysis) Dropsondes and Doppler radar (dual-Doppler analysis)

Motivation for RAINEX How do interactions of environment, eyewalls, and rainbands in the mature storm… …lead to intensity changes like these? Intensity of Katrina (2005) Max Wind Speed (knots) August