5.32 Estimating regions of tropopause folding and clear-air turbulence with the GOES water

vapor channel

Tony Wimmers, Wayne FeltzCooperative Institute for Meteorological Satellite Studies (CIMSS), UW-Madison

World Weather Research Symposium on Nowcasting and Very Short Range Forecasting

Toulouse, France, 5-9 Sept, 2005

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150

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600700

(~100 km)

subtropicalair mass

polar air mass

stratosphere

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tropopause

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CAT and tropopause folds

Upper-air front

Abstract: Clear-air turbulence remains a significant aviation hazard, yet by its nature it is very difficult to detect. One of the sources of clear-air turbulence is the dynamic instability associated with “tropopause folding”, which describes the

entrainment of stratospheric air into tropospheric levels at upper-level fronts. We describe a near real-time satellite product that estimates areas of tropopause folding in regions of strong humidity gradients in the GOES midwave

infrared (water vapor) channel. Using an empirical relationship between upper tropospheric humidity gradients and tropopause breaks, the algorithm estimates that turbulence-generating tropopause folds protrude from some of these

tropopause breaks. This product is validated over the United States with manual pilot reports as well as newer automated aircraft reports of turbulence.

longitude

lati

tud

e

Building a statistical model

Vertical component of the fold

subtropicalair mass

polar air mass

stratosphere

tropopause

Upper-air front

surface

+15K

-5K

Web product: Real-time pirep validation

Pirep data is provided courtesy of NCAR Aviation Digital Data Service (ADDS)

Web product: Real-time TAMDAR validation

TAMDAR (Tropospheric Airborne Meteorological Data Report) is part of the Great Lakes Field Experiment

Unfortunately, it is mostly lower and midtroposphere

http://cimss.ssec.wisc.edu/asap/exper/tfoldsVer2/pirepSep.html

http://cimss.ssec.wisc.edu/asap/exper/tfoldsVer2/tamdarDisplay.html

Web pages:

April 8-30, 2005 1500-2300 UTC (peak time)

Eastern U.S. (away from mountain wave turbulence)

Above 15,000 feet (mid- and upper troposphere)

Areas of strong convection are filtered out (no C.A.T.)

If the pirep is in a modeled fold and reports turbulence, then this is a correctly classified “Yes” report. If the pirep is outside a modeled fold and reports no turbulence, this is a correctly classified “No” report.

2,293 pirep observations, 62% of ALL observations are turbulent.

Validation: Details

Find the model’s “Probability of Detection” for turbulence

Next, search for any further constraints on the model that improve the Probability of Detection

Validation: Method

Number of Yes reports

Proportion of Yes reports correctly classified

Proportion of No reports

mis-classified*

1. Initial model 296 0.77 0.63

2. Revised model: Longer folds

240 0.78 0.63

3. Revised model (#2): Longer folds, higher

gradients138 0.82 0.63

* Does not purport to classify all negative reports

Statistics for tropopause fold turbulence prediction (N=2293, “background” rate of success=0.64)

The tropopause folding model shows significant skill at predicting upper-tropospheric turbulence

The model increases in accuracy significantly as it is made more selective (Prob of Detection = 82%)

Predicted turbulence is predominantly “light” or “moderate”

Preliminary conclusions: Trop folding + CAT

subtropicalair mass

polar air mass

stratosphere

Upper-air front