1. 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

2. 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

3. 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?

4. Miami Swan Island San Juan, Grand Cayman Guadeloupe The Jordan Mean Tropical Sounding (1958) 10 yr dataset (1946-1955) Averaged over the months of the “hurricane season”: July-Oct 1995-2002 ( July-October) 6,000 Caribbean rawinsondes 3,000 GOES images processed

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

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

7. Midwest T-storm Tropical Cyclone Duration ~30 min~5 days (named) Size ~15 mi ~300-400 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

8. 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

9. Shear: 10kt @5 Shear (12z): 15kt @258 Shear (18z): 23kt @243 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

10. 14 Sep 2007 1127 UTC 14 Sep 2007 1632 UTC Tropical Storm Ingrid 14 Sept 2007

11. 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

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

13. Tropical Storm Dolly: 21 July 2008 G-IV Synoptic Surveillance Mission 080721N Photo credit: Paul Flaherty NOAA/AOC

14. Hunting for Arc Clouds Arc Clouds Arc Cloud

15. 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)

16. 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