Arc Clouds in the Tropical Cyclone Environment

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

• 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
Downdrafts lead 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-level outflow
• c) bringing cool, dry air down into the
  boundary layer

9
Hurricane Isabel September 2003
10
Tropical Storm Ingrid 14 Sept 2007
14 Sep 2007 1127 UTC
14 Sep 2007 1632 UTC
11
Arc Clouds (contd)
Felix 07
Fabian 03
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 (contd)
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
15

• Simple Cloud Model (DeMaria) MT/SAL/MLDAI
• Parcel initialized at z0 with a 10 m/s updraft
  (r500 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-level outflow
• c) bringing cool, dry air down into the
  boundary layer

• Future Work
• -Conduct HRDs 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