Detecting turbulence from Satellites

September 13th, 2011 |
GOES Water Vapor Imagery and turbulence reports

GOES Water Vapor Imagery and turbulence reports

Clear Air Turbulence can be a significant aircraft hazard, occasionally causing injuries and long delays. (See, for example, here and here for two recent examples. The second example resulted in a 6-hour delay (Link))

At the upper-tropospheric boundary between air masses, vertical shearing at the jet stream combined with the ageostrophic convergence of polar, subtropical and stratospheric air produces a region known for its potential for clear air turbulence called a “tropopause fold.” These features are evident in satellite-observed upper tropospheric water vapor by the large-scale spatial gradients in brightness temperature, which define boundaries between the air masses. The tropopause fold extends from this boundary to a limited distance into and underneath the wetter air mass.

Thus, water vapor imagery can be used to infer large changes in vertical motion that can herald the presence of turbulence in the atmosphere. For example, in the region of turbulence shown in the water vapor imagery above, the yellow enhancement — warm brightness temperatures — suggest water vapor concentrated lower in the atmosphere (subsidence); bluer enhancements — colder brightness temperatures — suggest water vapor that is concentrated higher in the atmosphere (rising motion).

The Tropopause Folding Turbulence Prediction (TFTP) product locates these regions in the atmosphere and identifies the sections most likely to produce turbulent flight conditions for aircraft. The upper-tropospheric water vapor channel of the GOES-R Advanced Baseline Imager (primary: channel 8, backup: channel 9) is the source for resolving gradients that reveal the horizontal distribution of tropopause folds. An ancillary numerical weather model constrains these features vertically in the atmosphere. The four key output products consist of two fields that define the lower and upper bounds of the turbulent volumes of air, and two fields that define the two flight directions that are the most susceptible to moderate or greater turbulence. For now, the GOES-East (or MODIS) water channels can be used as a proxy.

GOES Water Vapor Imagery and turbulence reports

GOES Water Vapor Imagery and turbulence reports

The animated gif above shows the predicted tropopause fold (green), model results that show the tropopause (yellow, the 1-2 PV Unit surface) for a turbulence event that occurred in September 2011 (link). Note that the strongest turbulence (red airplane icon) occurred as the plane traversed the fold.

GOES-13 6.5 µm water vapor channel images (click image to play rocking animation)

GOES-13 6.5 µm water vapor channel images (click image to play rocking animation)

The animation of water vapor imagery (above) centered on the time of the turbulence includes some key features. For example, the gradient in the water vapor field between the colder brightness temperatures over the Atlantic Ocean south of New England and the warmer brightness temperatures off the coast of New Jersey is tightening with time. There is also evidence of a jet feature propagating northeastward along the gradient from east of the mouth of Chesapeake Bay at the start of the loop to south of Long Island at the end of the loop. Both of these features are suggestive of an evolving tropopause fold.

Pagami Creek wildfire in northeastern Minnesota

September 12th, 2011 |
MODIS true color and false color RGB images (11 September)

MODIS true color and false color RGB images (11 September)

MODIS true color and false color RGB images (12 September)

MODIS true color and false color RGB images (12 September)

250-meter resolution MODIS true color and false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) showed the very large pyrocumulus and smoke plume from the Pagami Creek wildfire that was burning in the Boundary Waters Canoe Area Wilderness region of northeastern Minnesota on 11 September 2011 and 12 September 2011. The wildfire “hot spot” appears as the large red-colored feature on the false color images.  Other options for viewing this MODIS imagery include the SSEC Web Mapping Service and WisconsinView sites: WMS MODIS image | WisconsinView: Terra and Aqua MODIS images.

A comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible channel, 3.7 µm shortwave IR channel, and 11.0 µm IR window channel data (below) revealed the very large fire “hot spot” on the shortwave IR image (red to yellow to black color enhancement) — and also note that the resulting pyrocumulus cloud just east of the fire hot spot exhibited a cloud top 11.0 µm IR window brightness temperature of -70º C (black color enhancement), which was just as cold as that associated with the thunderstorms farther to the north in Ontario, Canada!

MODIS 0.65 µm visible, 3.7 µm shortwave IR, and 11.0 µm IR images

MODIS 0.65 µm visible, 3.7 µm shortwave IR, and 11.0 µm IR images

AWIPS images of GOES-13 3.9 µm shortwave IR data (below) showed the diurnal changes to the size and intensity of the fire hot spot. Early in the animation during the overnight and morning hours, the hot spot was smaller and less intense as the wind speeds became very light– however, once strong southwesterly winds began to increase during the afternoon hours in advance of an approaching cold front, the hot spot was seen to dramatically increase in size as the fire quickly grew.

GOES-13 3.9 µm shortwave IR images (click image to play animation)

GOES-13 3.9 µm shortwave IR images (click image to play animation)

A comparison of the 4-km resolution GOES-13 3.9 µm and the 1-km resolution MODIS 3.7 µm shortwave IR images (below) demonstrated the advantage of better spatial resolution for more accurate location of the fire hot spot boundaries. In addition, the MODIS image revealed another small fire hot spot could be seen to the north, just across the Minnesota/Ontario border — this small fire was not seen on the GOES-13 image.

MODIS 3.7 µm and GOES-13 3.9 µm shortwave IR images

MODIS 3.7 µm and GOES-13 3.9 µm shortwave IR images

===== 13 September Update =====

A significant amount of smoke was transported southeastward across Wisconsin on 13 September 2011, as seen on GOES-13 0.63 µm visible channel images (below). The surface visibility was reduced to 2 miles at Milwaukee (station identifier KMKE), and 3 miles at Chicago O’Hare (station identifier KORD). Special Weather Statements were issued by the National Weather Service forecast offices at Milwaukee/Sullivan and Chicago/Romeoville to advise the public about the potential harmful effects of the smoke.

GOES-13 0.63 µm visible images (click image to play animation)

GOES-13 0.63 µm visible images (click image to play animation)

 

The smoke feature was even more apparent on the afternoon MODIS true color Red/Green/Blue (RGB) image (below), and this smoke produced an elevated signal on the MODIS Aerosol Optical Depth (AOD) product from the IDEA site.

MODIS true color Red/Green/Blue (RGB) image

MODIS true color Red/Green/Blue (RGB) image

CIMSS participation in GOES-R Proving Ground activities includes making a variety of MODIS images and products available for National Weather Service offices to add to their local AWIPS workstations. Currently there are 49 NWS offices receiving MODIS imagery and products from CIMSS.

Tropical Storm Nate

September 10th, 2011 |
GOES-13 10.7 µm IR images

GOES-13 10.7 µm IR images

GOES-13 10.7 µm IR images from the CIMSS Tropical Cyclones site (above) showed increasing convective banding within the eastern semicircle of Tropical Storm Nate as the system was undergong a period of intensification on 10 September 2011.

Deep layer wind shear was light over the region (below), which was a factor that aided in the intensification of the tropical cyclone.

GOES-13 IR image + 200-850 hPa deep layer wind shear product

GOES-13 IR image + 200-850 hPa deep layer wind shear product

A TRMM 85 GHz microwave image from 16:12 UTC (below) showed the band of deep convection withn the southeastern quadrant of Nate.

TRMM 85 GHz microwave image

TRMM 85 GHz microwave image

The GOES-13 satellite had been placed into Super Rapid Scan Operations (SRSO), providing bursts of 1-minute interval imagery. A sample of GOES-13 0.63 µm visible channel SRSO images (below; click image to play animation) showed the development of the convective bands wrapping around the center of the tropical cyclone. Early in the animation, you can also see the hazy appearance of the water to the east of Nate (off the west coast of the Yucatan Peninsula of Mexico) — this enhanced turbidity was the result of persistent strong southerly winds across those waters as Nate developed and moved very slowly across the region.

GOES-13 0.65 µm visible channel SRSO images (click image to play animation)

GOES-13 0.65 µm visible channel SRSO images (click image to play animation)

Upwelling of cold water along the eastern shore of Lake Michigan

September 7th, 2011 |
Comparison of 8-day average MODIS SST (left) and 07 September MODIS SST (right)

Comparison of 8-day average MODIS SST (left) and 07 September MODIS SST (right)

 

A comparison of the MODIS 8-day average Sea Surface Temperature (SST) ending on 06 September 2011 (above, left) with the MODIS SST product on 07 September 2011 (above, right) revealed a dramatic cooling of the near-shore waters just off the east coastline of Lake Michigan. Persistent strong northerly daytime winds (gusting in the 20-30 mph range) induced an upwelling of colder water from below the surface, with 07 September values as cold as 6.8ºC (44ºF) at one location (Latitude/Longitude 43.63 North/81.96 West) — compared to the previous 8-day average SST of 22.8ºC (73ºF) at that same location. Unfortunately, the MODIS Cloud Mask that is applied to the SST product mistakenly identifies the strongest SST gradient as a cloud, and blanks out the SST product along the far western fringe of the ribbon of colder water.

AWIPS images of MODIS 0.65 µm visible channel and 11.0 µm IR channel data (below) showed greater detail in the ribbon of colder waters, with a series of eddies forming along the northern edge of the feature. Since no Cloud Mask is applied to the IR image, the full westward extent of the cold water feature can be seen.

 

MODIS 0.65 µm visible channel and 11.0 µm IR channel images

MODIS 0.65 µm visible channel and 11.0 µm IR channel images

 

A sequence of four MODIS 11.0 µm IR images (below) shows the evolution of the eddy features along the western edge of the cold water. Note that the land surfaces exhibit cool IR brightness temperatures (blue to cyan color enhancement) on the first 2 night-time images (03:10 UTC and 07:21 UTC, or 10:10 pm and 2:21 am local time), but on the 2 daytime images (16:45 UTC and 18:27 UTC, or 11:45 am and 1:27 pm local time) urban areas and regions with less dense vegetation heat up and exhibit much warmer IR brightness temperatures (orange to red color enhancement). However, the Lake Michigan IR brightness temperatures generally remain constant during this time period.

MODIS 11.0 µm IR images

MODIS 11.0 µm IR images

 

CIMSS participation in GOES-R Proving Ground activities includes making a variety of MODIS images and products available for National Weather Service offices to add to their local AWIPS workstations. Currently there are 49 NWS offices receiving MODIS imagery and products from CIMSS. In addition, the VISIT training lesson “MODIS Products in AWIPS” is available to help users understand these products and their applications to weather analysis and forecasting.