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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

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Arc Clouds in the Tropical Cyclone Environment


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    1. Arc Clouds in the Tropical Cyclone Environment Jason P. Dunion1, Jeff Hawkins2, and Chris Velden3 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. The Jordan Mean Tropical Sounding (1958) 10 yr dataset (1946-1955) Averaged over the months of the “hurricane season”: July-Oct Grand Cayman Guadeloupe • 1995-2002 (July-October) • 6,000 Caribbean rawinsondes • 3,000 GOES images processed Miami San Juan, Swan Island

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

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

    7. Arc Clouds: Thunderstorms vs TCs Midwest T-storm Tropical Cyclone Duration ~30 min ~5 days (named) Size ~15 mi ~300-400 mi Motion ~25-30 kt ~10-12 kt Downdraftslead to dissipation phase disruption to the system *TCs have to stick it out in their environment*

    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-leveloutflow c) bringing cool, dry air down into the boundary layer

    9. Hurricane Isabel: September 2003 Shear: 10kt @5 Shear (12z): 15kt @258 Shear (18z): 23kt @243 16 Sept 1740 UTC All 3 new soundings: ~95-96% of column moisture is below 500 hPa TPW: MT=51.5 mm; SAL=40mm; MLDAI=36 mm

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

    11. Arc Clouds (cont’d) Fabian ‘03 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

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

    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 • 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-leveloutflow • c) bringing cool, dry air down into the boundary layer • 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