Arc Clouds in the Tropical Cyclone Environment
Jason P. Dunion1, Jeff Hawkins2, and Chris Velden3
1 NOAA/AOML/Hurricane Research Division2 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 (1946-1955)
Averaged over the months of the “hurricane season”: July-Oct1995-2002 (July-October)
•6,000 Caribbean rawinsondes•3,000 GOES images processed
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All Soundings (1995-2002; N=6,000)
Jordan (1958)
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MT (66%; N=3980)SAL (26%; N=1564)MLDAI (8%; N=455)Jordan (1958)
New Mean Moisture SoundingsMoist Tropical, SAL, and Mid-latitude dry air intrusions
Arc Clouds…aka Arcus Clouds(Roll Cloud; Shelf Cloud)
Arc Clouds
Arc Clouds
Arc Clouds
Midwest T-storm Tropical CycloneDuration ~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
Arc Clouds
Hypotheses1. 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 locallyb) promoting low to mid-level outflow c) bringing cool, dry air down into the boundary layer
Shear: 10kt @5
Shear (12z): 15kt @258Shear (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
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14 Sep 2007 1127 UTC
14 Sep 2007 1632 UTC
Tropical Storm Ingrid14 Sept 2007
Arc Clouds (cont’d)
Felix ‘07
Vertical ShearT(-24): 285/11 ktT(0): 280/15 kt
Low to Moderate Westerly
Vertical ShearT(-24): 140/11 ktT(0): 331/6 kt kt
SE to NNW
Fabian ‘03
Arc Clouds (cont’d)
Paloma ‘08
Vertical ShearT(-24): 156/2 ktT(0): 219/12 kt
SSE to SW
Tropical Storm Dolly: 21 July 2008G-IV Synoptic Surveillance Mission 080721N
Photo credit: Paul Flaherty NOAA/AOC
Hunting for Arc Clouds
Arc Clouds
Arc Cloud
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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
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Conclusions
• Future Work-Conduct HRD’s Arc Cloud module (P-3s, G-IV, Aerosonde)
a) arc cloud-TC relationshipb) 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 locallyb) promoting low to mid-level outflow c) bringing cool, dry air down into the boundary layer