Mesovortex over Lake Ontario

February 17th, 2015
GOES-13 0.63 µm visible channel images (click to play animation)

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

GOES-13 (GOES-East) 0.63 µm visible channel images (above; click to play animation) revealed the presence of a mesocale vortex (“mesovortex”) propagating eastward across the ice-free waters of western Lake Ontario on on 17 February 2015. At the beginning of the animation, also note that there were numerous “hole punch clouds” seen in the stratus cloud deck that covered the western Lake Ontario region during the early morning hours; these holes were likely caused by aircraft inbound/outbound from the Toronto International Airport — particles in jet engine exhaust act as ice nuclei, causing supercooled water droplets to turn into larger, heavier ice particles which then fall out of the cloud to create holes (sometimes described as “fall streaks” due to their appearance).

A closer view using a sequence of MODIS and VIIRS true-color Red/Green/Blue (RGB) images from the SSEC RealEarth web map server site is shown below. There was a significant amount of ice in the northeastern section of Lake Ontario, as well as a ring of offshore ice around other parts of the lake.

MODIS and VIIRS true-color images

MODIS and VIIRS true-color images

A comparison of the 16:31 UTC Terra MODIS 0.65 µm visible channel and the corresponding Sea Surface Temperature product (below) showed that SST values in the ice-free portions of the mesovortex path were generally in the 30 to 34º F  range.

Terra MODIS 0.65 µm visible channel image and Sea Surface Temperature product

Terra MODIS 0.65 µm visible channel image and Sea Surface Temperature product

Turbulence caused by mountain waves and jet stream wind shear

January 30th, 2015
GOES-13 6.5 µm water vapor channel images (click to play animation)

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

GOES-13 6.5 µm water vapor channel images (above; click to play animation) showed dry air (brighter yellow to orange color enhancement) moving across the Mid-Atlantic and Southeast regions of the eastern US in the wake of a strong cold frontal passage on the morning of 30 January 2015. There were also numerous pilot reports of turbulence, at both low altitudes (plotted in red) and high altitudes (plotted in cyan).

The most obvious feature seen on the GOES-13 water vapor images was the “rippled” signature of mountain waves, which extended far to the lee (southeast) of the Appalachian Mountains (the topographical obstacle to the strong northwesterly boundary layer flow that was causing the waves to initially form). A comparison of 4-km resolution GOES-13 6.5 µm water vapor and 1-km resolution Aqua MODIS 6.7 µm water vapor images (below) demonstrated the benefit of higher spatial resolution for diagnosing the areal coverage of such small-scale mountain waves. Of special note is the pilot report of “severe to extreme” turbulence at 4000 feet over South Carolina.

MODIS 6.7 µm and GOES-13 6.5 µm water vapor channel images, with pilot reports

MODIS 6.7 µm and GOES-13 6.5 µm water vapor channel images, with pilot reports

A comparison of the MODIS 6.7 µm water vapor channel image with the corresponding MODIS 0.65 µm visible channel image (below) showed that the severe to extreme reports in North and South Carolina were examples of Clear Air Turbulence (CAT), since no clouds were apparent in those areas at the time.

Aqua MODIS 0.65 µm visible channel and 6.7 µm water vapor channel images

Aqua MODIS 0.65 µm visible channel and 6.7 µm water vapor channel images

Regarding the numerous high-altitude pilot reports of moderate to severe turbulence, the NAM80 model depicted a 120-knot jet streak over South Carolina at 12:00 UTC, with another 120-knot jet streak approaching from the middle Mississippi Valley region (below). Note that there was strong wind speed shear to the north of the jet stream axis, which is where the bulk of the pilot reports of turbulence were located. Quite often there is an obvious moist-to dry gradient water vapor signature along or just poleward of a strong jet streak axis — but such a signature was not seen with this particular event.

GOES-13 water vapor image with NAM80 250 hPa wind isotachs and pilot reports

GOES-13 water vapor image with NAM80 250 hPa wind isotachs and pilot reports

In response to some of these pilot reports, at 16 UTC a SIGMET (SIGnificant METeorological advisory) was issued for occasional severe turbulence due to jet stream wind shear (below).

GOES-13 water vapor image with pilot reports and  boundaries of turbulence SIGMET

GOES-13 water vapor image with pilot reports and boundaries of turbulence SIGMET

4-panel images showing the three GOES-13 Sounder water vapor channels (6.5 µm, 7.0 µm, and 7.4 µm) along with the conventional GOES-13 Imager 6.5 µm water vapor channel (below; click to play animation) showed how each channel helped to identify where the pockets of middle-tropospheric dry air were located.

4-panel images showing the three GOES-13 Sounder and the GOES-13 imager water vapor channels (click to play animation)

4-panel images showing the three GOES-13 Sounder and the GOES-13 imager water vapor channels (click to play animation)

The GOES-13 water vapor channel weighting functions plotted using data from the 12 UTC rawinsonde reports from Roanoke/Blacksburg, Virginia and Greensboro, North Carolina are shown below. Due to the very dry middle to upper troposphere, the water vapor channels were able to sense features farther down into the atmosphere than is usually the case — this is illustrated by the relatively low altitude of the water vapor weighting function peaks.

Roanoke/Blacksburg, Virginia water vapor channel weighting function plots

Roanoke/Blacksburg, Virginia water vapor channel weighting function plots

Greensboro, North Carolina water vapor channel weighting functions

Greensboro, North Carolina water vapor channel weighting functions

Compare the 2 examples above with the altitude peaks of the various GOES-13 Sounder and Imager water vapor channels under “normal” conditions, plotted using the US Standard Atmosphere as the sounding profile (below).

GOES-13 water vapor channel weighting functions, calculated using the US Standard Atmosphere sounding profile

GOES-13 water vapor channel weighting functions, calculated using the US Standard Atmosphere sounding profilek

The trans-Atlantic flow of moisture and strong winds

January 14th, 2015
SSEC RealEarth™ Infrared satellite image featured on NBC Nightly News

SSEC RealEarth™ Infrared satellite image featured on NBC Nightly News

The SSEC RealEarth geostationary satellite infrared (IR) image composite shown above (which was first sent out via Twitter by Stu Ostro of The Weather Channel…thanks Stu!) was featured on the NBC Nightly News on 14 January 2015 (link) because it illustrated a vivid example of the trans-Atlantic flow of moisture from a disturbance off the US East Coast to a rapidly-deepening storm approaching the British Isles (surface analysis maps | water vapor images with surface analyses).

A sequence of hourly geostationary satellite water vapor channel image composites (below; click to play animation) showed that there was a clear trans-Atlantic connection in terms of middle to upper tropospheric moisture/clouds, and a comparison of the 20 UTC water vapor image with the corresponding MIMIC Total Precipitable Water product indicated that there was a lower to middle tropospheric moisture connection as well. This type of long and narrow fetch of TPW is often referred to as an “atmospheric river”.

Geostationary satellite water vapor image composites (click to play animation)

Geostationary satellite water vapor image composites (click to play animation)

Another interesting point brought up during the NBC Nightly News segment was the recent presence of unusually strong trans-Atlantic jet stream winds, which has allowed aircraft flying from New York City to London to set record times in terms of conventional passenger aircraft (such as the 08 January flight of British Airways 114). Note the strong dry-to-moist (darker blue to white to green color enhancement) along the northern edge of the trans-Atlantic water vapor image moisture feed: such a moisture gradient often coincides with the axis of a strong jet stream. AWIPS images of water vapor imagery with overlays of MADIS cloud-tracked and water-vapor-tracked winds (below; click image to play animation) showed many high-altitude wind vectors in the vicinity of the jet stream moisture gradient with speeds in the 150-160 knot range (with 175 knots seen on the previous day).

Water vapor images with MADIS atmospheric motion vectors (click to play animation)

Water vapor images with MADIS atmospheric motion vectors (click to play animation)

Did weather play a role in the crash of AirAsia Flight 8501?

December 27th, 2014
SSEC RealEarth fade between the regional map and the 23:00 UTC MTSAT-2 10.8 µm IR image

SSEC RealEarth fade between the regional map and the 23:00 UTC MTSAT-2 10.8 µm IR image

During the northwestward flight of AirAsia 8501 from Surabaya, Indonesia to Singapore, contact was lost with the aircraft over the Java Sea (likely east of the island of Pulau Belitung) on 28 December 2014 (late 27 December UTC time). Using the SSEC RealEarth web map server site, a fade between the regional map and the MTSAT-2 10.8 µm IR image at 23:00 UTC is shown above. The satellite image revealed that there were clusters of deep convection (thunderstorms with very high, very cold cloud tops) over the middle portion of the flight path.

COMS-1 10.8 µm IR channel images (click to play animation)

COMS-1 10.8 µm IR channel images (click to play animation)

COMS-1 10.8 µm IR channel images (above; click to play animation; also available as an MP4 movie file) indicated that the coldest cloud-top IR brightness temperatures were in the -80º to -85ºC range (violet color enhancement) with these thunderstorms. The location of Surabaya, Indonesia (station identifier WARR) and Singapore (station identifier WSSS) are annotated on the images; the last point of contact (at 23:24 UTC) was approximately within the circle drawn just to the left of the center of the images, when the aircraft was flying at an altitude of 32,000 feet (9.75 km) over the Java Sea. There were reports from various media sources that the pilots had requested to divert their flight path and climb to a higher altitude to avoid adverse weather conditions not long before contact was lost.

The corresponding COMS-1 0.675 µm visible channel images (below; click to play animation; also available as an MP4 movie file) showed evidence that there were some overshooting tops associated with these thunderstorms.

COMS-1 0.675 µm visible channel images (click to play animation)

COMS-1 0.675 µm visible channel images (click to play animation)

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MTSAT-2 10.8 µm IR channel image (click to enlarge)

MTSAT-2 10.8 µm IR channel image (click to enlarge)

Given that there was a long gap in available COMS-1 images (between 23:00 and 23:45 UTC), a closer view is shown using the 23:32 UTC MTSAT-2 10.8 µm IR channel (above) and 0.675 µm visible channel images (below). A circle is again drawn near the center of the MTSAT-2 images to denote the approximate location of final radar contact with the aircraft at 23:24 UTC — and the intended final destination of Singapore (WSSS) is labelled in the upper left corner of the images. Similar to what was seen in the COMS-1 images, the coldest cloud-top IR brightness temperature in the area at that time was -81.4ºC, and there was evidence of overshooting tops in the near vicinity on the visible image. (Note: due to the far southern location just below the Equator, the flight region on the 22:00 COMS-1 image was actually being scanned around 22:07 UTC, while on the 22:32 UTC MTSAT-2 image the flight region was being scanned around 22:39 UTC).

MTSAT-2 0.675 µm visible channel image (click to enlarge)

MTSAT-2 0.675 µm visible channel image (click to enlarge)

A nearby rawinsonde report from Pangkalpinang (station identifier 96237 on the MTSAT-2 images) showed that the aircraft cruising flight level of 32,000 feet was near 300 hPa (9750 meters above ground level), where the air temperature was -29.3ºC and winds were from the west-southwest at 16 knots (below). The tropopause appeared to be around 100 hPa (at a height of 54,265 feet or 1654 km), with an air temperature of -86.5ºC — close to the coldest cloud-top IR brightness temperatures seen on the COMS-1 and MTSAT-2 IR images. Moisture was abundant throughout the atmospheric column, with a Total Precipitable Water value of 52.4 mm or 2.1 inches.

Pangkalpinang, Indonesia rawinsonde report

Pangkalpinang, Indonesia rawinsonde report

MTSAT-2 water vapor image derived atmospheric motion vectors from the CIMSS Tropical Cyclones site (below) showed that upper-tropospheric winds over the flight region (located at the far top center portion of the images) before, during, and after the flight time were generally southwesterly to westerly in the 15-30 knot range.

MTSAT-2 6.57 µm water vapor channel images with upper-tropospheric atmospheric motion vectors

MTSAT-2 6.57 µm water vapor channel images with upper-tropospheric atmospheric motion vectors

Deep convection is not uncommon in this region during this time of the year, when the Intertropical Convergence Zone (ITCZ) migrates southward during the Southern Hemisphere summer season. The presence of warm sea surface temperatures along with abundant Total Precipitable Water over western Indonesia (below) helps to create an environment that is favorable for the growth and maintenance of large thunderstorms.

Global image of Sea Surface Temperatures on 27 December

Global image of Sea Surface Temperatures on 27 December

25-27 December MIMIC Total Precipitable Water product (click to play animation)

25-27 December MIMIC Total Precipitable Water product (click to play animation)

For an additional detailed meteorological analysis of this event, see the Weather Graphics site.

===== 30 December Update =====

Map of AirAsia Flight 8501, and location of initial debris (credit: New York Times)

Map of AirAsia Flight 8501, and location of initial debris (credit: New York Times)

On the third day of the search, aircraft debris and bodies of passengers were discovered about 66 miles southwest of the last known coordinates of AirAsia Flight 8501 (above). The prevailing ocean current in the Java Sea (below) may have displaced some of the debris southwestward from the actual crash site.

Map of ocean currents (credit: Columbia University Earth Institute)

Map of ocean currents (credit: Columbia University Earth Institute)

The Indonesian Bureau of Meteorology, Climate, and Geophysics (BMKG) released their meteorological analysis of the AirAsia 8501 crash on 31 December.