The use of satellite water vapor imagery and model output to

diagnose and forecast turbulent mountain waves

Nathan UhlenbrockSteve Ackerman

Wayne Feltz R. Sharman2, and J. Mecikalski3

11Cooperative Institute of Meteorological Satellite Studies (CIMSS)Cooperative Institute of Meteorological Satellite Studies (CIMSS)University of Wisconsin-MadisonUniversity of Wisconsin-Madison22NCARNCAR33University of AlabamaUniversity of Alabama

P5.30

Outline of Presentation

• Goals• Data used in the study• Mountain Waves in water vapor imagery• Case Studies• Conclusions and Future Work

Goal• Improve the use of satellite observations in nowcasting and

short term forecasting of turbulence affecting air traffic.

• One approach: Use model output and raobs to identify favorable regions of mountain wave turbulence, then use satellite observations to identify if the turbulence is present.

• What do identify?

Data• Satellite

– Terra and Aqua MODIS (1 km in infrared) – GOES-12 imagery– GOES ABI (2-km resolution); simulation

• Pilot Reports (PIREPS) of turbulence during 2004 over the Continental Unite States

• Model output from the RUC and GFS • Surface and upper air analyses and soundings

Data: Some Notes on PIREPS• PIREPS were used as a validation data set in this

study to “verify” that lee waves were occurring, but there are some known issues with the data

• PIREPS are subjective by nature; – a pilot can only report what he/she feels– The location of a reported turbulence event has errors

because the aircraft is moving quickly, and the pilots first responsibility is safety, not data reporting

– A region of turbulence will effect a Cesna 172 quite differently than a Boeing 777 due to scale factors

– PIREPS can only be issued by planes in the air, so few PIREPS are issued during the late night and early morning

Mountain Waves and Satellite Imagery

Cloud patterns indicate presence of mountain waves.

This example is visible image over eastern United States.

Mountain Waves and Satellite Imagery

Signature of wave activity is also found in cloud free regions in the water vapor channel.

Region of study is the front range of the Rocky Mountains in Colorado, USA

Mountain waves

Mountain Waves and Satellite Imagery

Signature of wave activity is also found in cloud free regions in the water vapor channel.

Region of study is the front range of the Rocky Mountains in Colorado, USA

Mountain waves

Mountain Waves and Satellite Imagery• MODIS 6.7 micron imagery over CO was analyzed for each day in 2004 for

wave signatures.• 89 days exhibited waves over Colorado in 2004 (about 1 out of 4 days in 2004).• The days that exhibited waves were grouped into qualitative categories dividing

the waves by:

• Amplitude (high/low)• Interference (some/none)• Wavelength (short/long)• Extent Downstream

Categorized with turbulence reports from pilots (above 12,000 feet).

Type 5

Sept. 09, 2004

Prominent wave events with no interference.

Type 5 Example

Sept. 09, 2004

Prominent wave events with no interference

Aqua MODIS water vapor imagefrom 1950Z March 06, 2004

(Colorado)

Type 6 example

Type 6 example

Aqua MODIS water vapor imagefrom 1950Z March 06, 2004

(Colorado)

Image analysis (2004)Type 1 Low amplitude, short extent 18 days/2 turb.

Type 2 Low amplitude, medium to long extent downstream, little or no ‘interference’

27/5

Type 3 low amplitude, medium to long extent downstream, moderate to high interference

15/7

Type 4 high amplitude, short extent downstream

9/5

Type 5 high amplitude, medium to long extent downstream, little or no interference

13/4

Type 6 high amplitude, medium to long extent downstream, moderate to high interference

7/6

Types 3 and 6

Aqua MODIS water vapor imagefrom 1950Z March 06, 2004

(Colorado)

Visible imagery showswaves in cloud free region

Conditions favorable for untrapped

mountain wave

Mar. 06 300mb flow

What altitude, how deep?

Weighting functions given a broad indication of level…

250-550mb

Water Vapor (6.7 micron)

What altitude, how deep?

14.2 micron

Wave appear to propagate vertically

6.7 micron 14.2 micron

Waves appeared earlier, but no ‘interference pattern’

6 March, 2004 0845Z 6 March, 2004 1950Z

Seen in Terra MODIS as well…

6 March, 2004 1810 (6.7 left, 11 right)

Conclusions and Future Work• There were many days with mountain waves that were not

reported with moderate/severe turbulent.• The majority of moderate/severe turbulent days (as determined

from PIREPS) over Colorado were due to lee waves• Days with waves exhibiting more complex patterns were also the

days with the most moderate to severe PIREPS of turbulence.

• Now that we know what to look for:– How to best recognize the features,– Are these signatures indications of breaking waves, interference, trapped

waves?