Arc Clouds in the Tropical Cyclone Environment Jason P. Dunion 1, Jeff Hawkins 2, and Chris Velden 3 1 NOAA/AOML/Hurricane Research Division 2 NRL-Monterey 3 UW-CIMSS

Discussion Outline Motivation Background - new mean soundings for the tropical NATL Arc Clouds - Midwest t - storms vs TCs - hypotheses (TCs) - arc clouds & TCs Future Work Conclusions

Motivation How does moisture and vertical wind shear in the surrounding TC environment impact TC intensity? …and where do arc clouds fit in to all this?

Miami Swan Island San Juan, Grand Cayman Guadeloupe The Jordan Mean Tropical Sounding (1958) 10 yr dataset ( ) Averaged over the months of the “hurricane season”: July-Oct ( July-October) 6,000 Caribbean rawinsondes 3,000 GOES images processed

New Mean Moisture Soundings Moist Tropical, SAL, and Mid-latitude dry air intrusions

Arc Clouds …aka Arcus Clouds (Roll Cloud; Shelf Cloud) Arc Clouds

Midwest T-storm Tropical Cyclone Duration ~30 min~5 days (named) Size ~15 mi ~ mi *TCs have to stick it out in their environment* Motion ~25-30 kt ~10-12 kt Arc Clouds: Thunderstorms vs TCs Downdrafts lead to dissipation phase disruption to the system

Arc Clouds Hypotheses 1. The moist tropical sounding is insufficiently dry in the mid- levels to form substantial arc clouds 2. Arc clouds inhibit TC development in the short term by: a) promoting downdrafts locally b) promoting low to mid-level outflow c) bringing cool, dry air down into the boundary layer

Shear: Shear (12z): Shear (18z): 16 Sept 1740 UTC Hurricane Isabel: September 2003 All 3 new soundings: ~95-96% of column moisture is below 500 hPa TPW: MT=51.5 mm; SAL=40mm; MLDAI=36 mm

14 Sep UTC 14 Sep UTC Tropical Storm Ingrid 14 Sept 2007

Arc Clouds (cont’d) Felix ‘07 Vertical Shear T(-24): 285/11 kt T(0): 280/15 kt Low to Moderate Westerly Vertical Shear T(-24): 140/11 kt T(0): 331/6 kt kt SE to NNW Fabian ‘03

Arc Clouds (cont’d) Paloma ‘08 Vertical Shear T(-24): 156/2 kt T(0): 219/12 kt SSE to SW

Tropical Storm Dolly: 21 July 2008 G-IV Synoptic Surveillance Mission N Photo credit: Paul Flaherty NOAA/AOC

Hunting for Arc Clouds Arc Clouds Arc Cloud

Simple Cloud Model (DeMaria): MT/SAL/MLDAI Parcel initialized at z=0 with a 10 m/s updraft (r=500 m) Parcel entrains environmental air along the way Entrainment coeff= 0.1 Height (km)

Conclusions Future Work -Conduct HRD’s Arc Cloud module (P-3s, G-IV, Aerosonde) a) arc cloud-TC relationship b) shear-dry air impacts on TCs (tag team effect) -Continue modeling studies using these 3 new soundings New mean soundings (tropical NATL & Caribbean) -Moist Tropical, SAL, and MLDAI -Distinguishing MT from SAL & MLDAI: 45 mm TPW Arc Clouds -Different implications: Midwest t-storms vs TCs -MT sounding: insufficiently mid-level dryness to form arc clouds -Disruption of TC via: a) promoting downdrafts locally b) promoting low to mid-level outflow c) bringing cool, dry air down into the boundary layer