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)

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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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Mid-lat dry air intrusion

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