Thermodynamic Structure Thermodynamic Structure of Tropical Cyclones From of Tropical Cyclones From Aircraft ReconnaissanceAircraft Reconnaissance

Kay SheltonUniversity at Albany/SUNY,

Albany, New York

• US Air Force reconnaissance flights.– Archive maintained by John Knaff (CIRA).

• 1995-2003, 77 storms 619 flights.• Equivalent potential temperature e.

– Bolton (1980).

• Case-study: Bret, 1999.– Comparison of e and windspeed through storm

evolution from tropical depression through to category 4 hurricane.

• Composite of all storms.– Data every 30s, averaged into 20km radial bins

– (>5 points per bin to be included)– Categorised average e profiles by level and

intensity.

DATA AND METHODOLOGYDATA AND METHODOLOGY

• Instrument wetting errors (IWE). – Eastin et al. (2002).

LIMITATIONLIMITATION

Adapted from Eastin et al. 2002b

• IWE minimised away from eyewall.

• In eyewall, maximum mean error < 3K.

• Removal of IWE acts to move maximum radial gradient towards outer edge of eyewall.

• Errors may be larger for individual cases.

• Hurricane Bret, 1999.

– Organised to TD at 18Z on 18th August, in Bay of Campeche.

– Bret strengthened to category 4, then decreased to category 3 prior to landfall on Padre Island, TX at 00Z on 23rd August.

– Scatter plots of e and windspeed in six flights will be shown.

CASE STUDYCASE STUDY

<500m TD-TS

TS <500m

<500m

<500m

e Windspeed

TS

H1-H2

~850hPa

~850hPa

~850hPa

~850hPa

37.5km

e Windspeed

H4

H4-H3

~700hPa

~700hPa~700hPa

~700hPa

17.8km

32.5km e Windspeed

COMPOSITECOMPOSITE

Intensity LevelMax. # Flights

TD <500m 52

<500m 138

~850hPa 115

~850hPa 73

~700hPa 67

H2 ~700hPa 47

H3 ~700hPa 47

H4 ~700hPa 34

TS

H1

• Flight level must increase as storms intensify.

• Weaker systems have fewer flights above PBL, stronger systems have fewer flights below 700hPa.

• Comparison between levels at a given intensity is limited to TS and H1.

COMPOSITE COMPOSITE INWARD RADIAL INWARD RADIAL GRADIENT OF GRADIENT OF ee -

e/

r (K/100km)

-

e/

r (K/100km)

-

e/

r (K/100km)

<500m

~850hPa ~700hPa

ee DIFFERENCE BETWEEN 2 DIFFERENCE BETWEEN 2 LEVELSLEVELS

TS: e(BL) – e(850hPa) H1: e(850hPa) – e(700hPa)

e (

K)

Arrows indicate relevant tropical environment e/p (Jordan, 1958)

SUMMARYSUMMARYRADIAL

• TD: |e/r| ~ 0 at all radii• TS: e increases first in the core (r<90km)• H1-H4: |e/r| increases with intensity, within

r=100km

VERTICAL• TS and H1: In lower troposphere convective

instability increases outward.– Both profiles are close to convective neutrality near

storm centre and convective instability increases outwards to their respective tropical environmental values.