5.1 micrometers and IASI

September 11th, 2022 |

A previous post discussed the 5.1 micrometer channel that might be part of the imager (GXI) to fly on GeoXO, the next-generation satellite (beyond GOES-R) to be launched in the 2030s. That previous post, however, used Cross-track Infrared Sounder (CrIS) data, and CrIS observes close to, but not at, 5.1 micrometers. However, the Infrared Atmospheric Sounding Interferometer (IASI) that is part of the payload on Metop-B and Metop-C (it was on Metop-A as well!) does take observations at 5.1 micrometers. The animation shows a Metop-A IASI observations at 5.1, 6.19, 6.9 and 7.3 micrometers (or wavenumbers 1950, 1615, 1438 and 1369) from a granule over Europe. Of note is apparent moisture aloft — shown as cooler brightness temperatures especially at 6.9 micrometers — that has no apparent signal at 5.1 micrometers because of less sensitivity to mid-tropospheric water vapor at the shorter wavelength. Indeed, 5.1 micrometer brightness temperatures are much warmer than the other channels.

Metop-A observations at 5.1, 6.19, 6.9 and 7.3 micrometers, 1140 UTC on 15 January 2007. (Click to enlarge)

A greyscaled image of 5.1 micrometers, below, shows how the boundary layer influences the signal in clear air.

5.1 micrometer image from IASI data (click to enlarge)

What did geostationary imagery look like on this day? Meteosat-8 imagery at 6.19 and 7.3 micrometers is shown below.

Meteosat-8 Bands 5 and 6 (6.2 and 7.3 micrometers) at 1930 UTC on 15 January 2007 (Click to enlarge)

How dry was this airmass over the Mediterranean? Soundings from 0000 and 1200 UTC on 15 January 2007 (link, from the Wyoming Sounding site) show total precipitable water values between 10 and 14 mm.

The addition of the 5.1 micrometer channel is designed to aid in convective forecasting: gradients in water vapor very low in the atmosphere should be apparent.

Tropical Cyclone Malakas in the western Pacific

April 8th, 2022 |
Himawari-8 Band 3 (Visible 0.64 µm) and Band 8 (infrared 6.24 µm) from 0630 to 0700 UTC on 8 April 2022 (Click to enlarge)

The tropical disturbance (formerly 95W) in the western Pacific south of Guam (discussed here) has strengthened and become the second western Pacific named storm of the year: Malakas. The storm is about halfway between the islands of Guam and New Guinea. The side-by-side imagery above, showing Himawari Band 3 and Band 8 imagery (courtesy JMA), shows deep convection near the center of the storm that was at fairly low latitudes: around 6o N at 0600 UTC on 8 April, the times of the imagery above. In addition, the storm is far from dry air. A 24-hour animation of the Band 3 (0.64 µm)/Band 13 (10.41 µm) sandwich product on 7 April 2022 below, taken from this site (see this blog post), shows the rotation of the system and the abundance of convection at the center.

HImawari-8 Sandwich Product, 0000-2350 UTC on 7 April 2022 (Click to enlarge)

The forecast at 1200 UTC on 8 April from the Joint Typhoon Warning Center take this strengthening storm northwest, between Guam and Yap.

Imagery from the SSEC/CIMSS Tropical Weather website, below, shows the storm in a region of low shear. An excellent ASCAT overpass at 1126 UTC on 8 April 2022 showed a closed-off center.

Malakas imagery from the SSEC/CIMSS Tropical Website, data valid between 1126 UTC (ASCAT) and 1500 UTC (Wind shear analysis) (Click to enlarge)

Polar Hyperspectral modeling of Severe Weather, Day 2

March 30th, 2022 |

Severe weather occurred over the Deep South on 31 March (see this blog post); NOAA’s Storm Prediction Center (SPC) showed a Moderate Risk of severe weather over a region centered on Alabama; the toggle above shows the Moderate Risk in combination with the Tornadic Probailities. Here are the storm reports for this event. The overlap between the risk area and severe weather is here (or here at the SPC website); the overlap between the risk area and observed tornadoes is shown below (and here at the SPC website).

Observed tornadoes and SPC Risk from 1630 UTC on 30 March 2022 (Click to enlarge)

This blog post discussed output from Polar Hyperspetral modeling and how it could be used the day before. The animation below shows the Significant Tornado Potential parameter forecast at 2100 UTC on 30 March from initializations at 1200, 1400, 1700, 1800 and 2000 UTC (that is, 90, 7-, 4-, 3- and 1-hour forecasts). The areal extent of the maximum STP values is decreasing with time. Storm Reports from 30 March suggest that tornadic activity after 2100 UTC was in Mississippi and Louisiana. In addition, the largest values of STP did not extend to the into the northern part of the Moderate Risk.

Significant Tornado Parameter forecast valid at 2100 UTC on 30 March; 9-h, 7-h, 4-h, 3-h and 1-h forecasts (Click to enlarge)

In addition to being in the local AWIPS at CIMSS, in preparation for the Hazardous Weather Testbed, model output is also available at this link. The 00-h through 08-h forecast Lifted Index and Significant Tornado Parameter for this event, initialized at 2100 UTC, are shown below. The forecast shows that although the thermodynamic forcing might be dropping — as measured by the Lifted Index — the low-level wind field is becoming more favorable, as measured by the increase of STP as the system moves into Alabama.

Forecast Lifted Index, 00-h through 08-h forecasts from 2100 UTC initial time, 30 March 2022 (Click to enlarge)
Forecast Significant Tornado Parameter, 00-h through 08-h forecasts from 2100 UTC initial time, 30 March 2022 (Click to enlarge)

Which polar orbiters provide data to this modeling effort? Both Metop-B and Metop-C, as well as Suomi-NPP and NOAA-20. A 2100 UTC model initialization will include data from the afternoon passes of Suomi-NPP and NOAA-20 (it generally takes at most an hour for the polar orbiting data to be incorporated into the Data Fusion initializations). You can view orbital paths from the Metop satellites, and from JPSS, at this website.

Tehuano wind event

March 12th, 2022 |

Visible images from GOES-17 (left) and GOES-16 (right) [click to play animated GIF | MP4]

As a strong arctic cold front moved southward across the Gulf of Mexico and southern Mexico (surface analyses) on 12 March 2022, the cold air passed through the Chivela Pass and emerged as a Tehuano (or “Tehuantepecer“) gap wind that fanned outward across the Gulf of Tehuantepec. Visible images from GOES-17 (GOES-West) and GOES-16 (GOES-East) showed the narrow arc cloud that marked the leading edge of this gap flow (above).

GOES-16 True Color RGB images [click to play animated GIF | MP4]

True Color RGB images created using Geo2Grid from GOES-16 (above) and GOES-17 (below) showed the hazy signature of blowing dust/sand as it was transported off the south coast of Mexico and spread out across the Gulf of Tehuantepec.

GOES-17 True Color RGB images [click to play animated GIF | MP4]

ASCAT surface scatterometer winds from Metop-B and Metop-C (source) are shown below; gap winds emerging from the coast were in the 35-40 knot range at 1631 UTC.

ASCAT winds from Metop-B and Metop-C [click to enlarge]