Pilot report: “Stronger winds than forecast”

April 5th, 2009 |
GOES-11 6.5 µm water vapor image + satellite winds + PIREP

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

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

GOES-13 6.5 µm water vapor images

Yet another Redoubt volcanic eruption

April 4th, 2009 |
GOES-11 visible, 3.9 µm IR, 10.7 µm IR, and IR spilt window difference images

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

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

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).

OMI SO2 24-hour composite image

AIRS OMI SO2 24-hour composite image

Blowing dust in northeastern Arizona

April 3rd, 2009 |
GOES-13 visible images

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 image

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