AWIPS image of GOES-11 6.7 µm water vapor + GOES satellite winds + PIREPs

There was a pilot report (or PIREP) received over Annette Island, Alaska (station identifier ANN) on 05 April 2009 which noted “stronger winds than forecast” at an altitude of 29,000 feet. The winds reported by the aircraft were from a direction of 190º at a speed of 76 knots — and nearby GOES-derived atmospheric motion vectors (above) generally had speeds of around 50 knots or less.

However, note the strong dry-to-moist (dark blue to white) gradient seen on the 8-km resolution GOES-11 water vapor imagery above — this is a common signature that often occurs along the axis of a strong jet streak. This strong water vapor gradient is more well-defined when viewed on a 1-km resolution MODIS water vapor image from 21:40 UTC (below).

MODIS 6.7 µm water vapor image

An animation of 4-km resolution GOES-13 6.5 µm water vapor imagery (below) also shows this strong “jet streak gradient” signature just to the west of Annette Island (ANN). Even though the viewing angle from the GOES-13 satellite (positioned over the Equator at 105º West longitude) was quite large, the 4 km spatial resolution of the data still allowed the gradient to show up quite well.

GOES-13 6.5 µm water vapor images

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GOES-11 visible, 3.9 µm IR, 10.7 µm IR, and IR "split window difference" images

The Mt. Redoubt volcano in Alaska experienced its 19th explosive event (in a series that began on 23 March) on 04 April 2009. GOES-11 visible, 3.9 µm shortwave IR (IR2), 10.7 µm IR window (IR4), and 10.7-11.0 µm “split window difference” images (above) showed that the southeastward advection of the volcanic plume became increasingly difficult to follow a few hours after the eruption.

However, the volcanic plume likely contained a good deal of water vapor, which made it easier to track on GOES-11 6.7 µm “water vapor channel” imagery (below) as it moved toward and eventually south of 50º N latitude  after about 21:00 UTC.

GOES-11 6.7 µm water vapor images

Images of the MODIS 1.3 µm “cirrus detection channel” at 20:45 and 22:35 UTC (below) exhibited a signal of the leading edge of the volcanic plume as it approached and moved south of 50º N latitude (between 144º W and 142º W longitude). This MODIS near-IR channel is sensitive to particles that are efficient scatterers of light (such as smoke, haze, dust, ash), so these types of airborne particles to show up as slightly brighter features on grayscale-enhanced MODIS “cirrus detection channel” imagery.

Terra and Aqua MODIS near-IR "Cirrus detection channel" images

The extent of the long-range transport of the Redoubt SO2 plume was even more obvious on the AIRS Ozone Monitoring Instrument (OMI) SO2 24-hour composite image for 04 April (below).

AIRS OMI SO2 24-hour composite image

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GOES-13 visible images

GOES-13 visible channel images (above) showed widespread blowing dust across much of northeastern Arizona on 03 April 2009. Surface winds in that region  gusted to 91 mph at Meteor Crater and 68 mph at Winslow. Note that the thick pall of airborne dust also appeared to be having the effect of limiting the development of cumulus clouds across northeastern Arizona (by reducing the amount of solar radiation reaching the surface).

AWIPS images of the MODIS “visible” channel, 2.1 µm near-IR “Snow/ice” channel, 11.0 µm “IR window” channel, and the 1.3 µm near-IR  “cirrus detection” channel (below) showed that the  bowing dust feature exhibited a signature on all four of those MODIS spectral bands. The dust plume was drifting into far southwestern Colorado, where surface visibility dropped to 2 miles at Cortez.

MODIS "visible", "snow/ice", "IR window", and "cirrus detection" images

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GOES-13 6.5 µm water vapor images

Another one for the “What the heck is this?” blog category. Jeff Craven (SOO at the Milwaukee/Sullivan NWS forecast office) pointed out in an email:

“The mid/high cloud deck in warm conveyor belt from OK into MO has an interesting strong subsident area over MO. It looks almost like a standing wave feature.”

GOES-13 6.5 µm “water vapor channel” images (above) showed this interesting feature, which was oriented approximately N-S across western Missouri for several hours during the day on 30 March 2009. Note how the middle and upper level clouds appeared to dissipate very quickly as they moved eastward across the “standing wave” feature.

There was a warm frontal boundary moving northward across that region, which was nearly perpendicular to the standing wave feature — so the orientation of that surface-based boundary appeared to be unrelated to the standing wave aloft. In addition, there did not appear to be any pilot reports of turbulence associated with this particular standing wave feature.

GOES-12 water vapor channel weighting function (Springfield MO)

According to the CIMSS GOES Weighting Functions site, calculations using 12 UTC rawinsonde data from Springfield MO indicated that the GOES-12 imager water vapor channel weighting function (black plot) was peaking around the 400 hPa pressure level (above) — so most features seen on the GOES imager water vapor channel data over that particular region were probably residing within the 300-500 hPa layer. However, a comparison of AWIPS images of the GOES-12 imager water vapor channel and the three GOES-12 sounder water vapor channels (below) revealed that the signature of this standing wave feature was a bit more well-defined on the GOES-12 sounder 7.4 µm water wapor images (whose weighting function peaked near the 500 hPa pressure level, as seen on the red plot above).

GOES-12 imager and sounder water vapor channel images

West-to-east oriented cross sections of RUC40 model fields (below) did not show any significant changes in the height of the dynamic tropopause over that region, but the yellow contours of potential temperature (especially the 315 K and 318 K contours) did exhibit a bit of a dip downward in the general area where the standing wave appeared on water vapor imagery (as if to suggest that there could have been some subsidence there, if the flow had indeed been adiabatic).

West-to-east oriented RUC40 model cross sections

As much as we hate to let Jeff down, that’s the best explanation we can conjure up at this time. If any of you blog readers have any other ideas which might help to explain why this feature was apparently acting as a “standing wave” for several hours, send us email!

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