Great Lakes surface geographical outlines evident on water vapor imagery

February 23rd, 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)

A cold and dry arctic air mass (morning minimum temperatures) was in place over the Great Lakes region on 23 February 2015. This arctic air mass was sufficiently cold and dry throughout the atmospheric column to allow the outlines of portions of the surface geography of the Great Lakes to be seen on GOES-13 (GOES-East) 6.5 µm water vapor channel images (above; click image to play animation).

In addition to the commonly-used 4-km resolution 6.5 µm water vapor channel on the GOES Imager instrument, there are also three 10-km resolution water vapor channels on the GOES Sounder instrument (centered at 6.5 µm, 7.0 µm, and 7.4 µm). A 4-panel comparison of these water vapor channel images (below; click image to play animation) provides the visual indication that each water vapor channel is sensing radiation from different layers at different altitudes — for example, the surface geographical outlines of the Great Lakes are best seen with the Sounder 7.4 µm (bottom left panels) and the Imager 6.5 µm (bottom right panels) water vapor channels.

GOES-13 Sounder 6.5 µm, 7.0 µm, 7.4 µm, and Imager 6.5 µm water vapor channel images (click to play animation)

GOES-13 Sounder 6.5 µm, 7.0 µm, 7.4 µm, and Imager 6.5 µm water vapor channel images (click to play animation)

An inspection of GOES Sounder and Imager water vapor channel weighting function plots (below) helps to diagnose the altitude and depth of the layers being sensed by each of the individual water vapor channels at a variety of locations. For example, the air mass over Green Bay, Wisconsin was cold and very dry (with a Total Precipitable Water value of 0.87 mm or 0.03 inch), which shifted the altitude of the various water vapor channel weighting functions to very low altitudes; this allowed surface radiation from the contrasting land/water boundaries to “bleed up” through what little water vapor was present in the atmosphere, and be sensed by the GOES-13 water vapor detectors. In contrast, the air mass farther to the south over Lincoln, Illinois was a bit more more moist, especially in the middle/upper troposphere (with a Total Precipitable Water value of 4.20 mm or 0.17 inch) — this shifted the altitude of the water vapor channel weighting functions to much higher altitudes (to heights that were closer to those calculated using a temperature/moisture profile based on the US Standard Atmosphere).

GOES-13 Sounder and Imager water vapor channel weighting function plots for Green Bay WI, Lincoln IL, and the US Standard Atmosphere

GOES-13 Sounder and Imager water vapor channel weighting function plots for Green Bay WI, Lincoln IL, and the US Standard Atmosphere

In addition to the temperature and/or moisture profile of the atmospheric column, the other factor which controls the altitude and depth of the layer(s) being detected by a specific water vapor channel is the satellite viewing angle (or “zenith angle”); a larger satellite viewing angle will shift the altitude of the weighting function to higher levels in the atmosphere. Recall that the water vapor channel is essentially an Infrared (IR) channel — it generally senses the mean temperature of a layer of moisture or clouds located within the middle to upper troposphere. In this case, the sharp thermal contrast between the cold land surfaces surrounding the warmer Great Lakes was able to be seen, due to the lack of sufficient water vapor at higher levels of the atmosphere to attenuate or block the surface thermal signature.

The new generation of geostationary satellite Imager instruments (for example, the AHI on Himawari-8 and the ABI on GOES-R) feature 3 water vapor channels which are similar to those on the current GOES Sounder, but at much higher spatial and temporal resolutions.

On a separate — but equally interesting — topic: successive intrusions of arctic air over the region allowed a rapid growth of ice in the waters of Lake Michigan. A 15-meter resolution Landsat-8 0.59 µm panochromatic visible image viewed using the SSEC RealEarth web map server (below) showed a very detailed picture of ice floes along the western portion of the lake, as well as a patch of land-fast ice in the far southern end of the lake.

Landsat-8 0.59 µm panochromatic visible image (click to enlarge)

Landsat-8 0.59 µm panochromatic visible image (click to enlarge)

The motion of the band of ice floes along the western  edge of Lake Michigan was evident in 1-km resolution GOES-13 0.63 µm visible channel images (below; click image to play animation) — along the east coast of Wisconsin, southwesterly winds gusting to around 20 knots were acting to move the ice floes away from the western shoreline of Lake Michigan.

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

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

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)

“River-effect” snow in South Dakota

November 13th, 2014
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 0.63 µm visible channel images (above; click image to play animation) revealed the presence of numerous cloud streamers originating over the Lake Oahe and Lake Sharpe reservoirs along the Missouri River in South Dakota on 13 November 2014. At times these cloud bands were producing snow that was reducing surface visibility to 4 miles at Pierre (KPIR) and 5 miles at Chamberlain (K9V9).

Aqua MODIS 0.65 µm visible channel image, False-color RGB image, and Sea Surface Temperature product at 19:48 UTC

Aqua MODIS 0.65 µm visible channel image, False-color RGB image, and Sea Surface Temperature product at 19:48 UTC

Comparisons of visible channel and false-color Red/Green/Blue (RGB) images from Aqua MODIS (above) and Suomi NPP VIIRS (below) demonstrated the value of RGB products to more easily identify such supercooled water droplet cloud features (which appear as varying shades of white) in areas that have underlying snow cover (which appears as varying shades of red). In addition, the MODIS Sea Surface Temperature (SST) product (above) showed that SST values were in the 40-50º F range (cyan color enhancement) in those Missouri River reservoirs, making them significantly warmer than the cold arctic air mass that had overspread the region.

Suomi NPP VIIRS 0.64 µm visible channel image and False-color RGB image at 19:51 UTC

Suomi NPP VIIRS 0.64 µm visible channel image and False-color RGB image at 19:51 UTC

Displaying NUCAPS data from CLASS

November 12th, 2014

NUCAPS data have been flowing into AWIPS 2 for months; in the recent past, these data started flowing into the NOAA CLASS data archive as well (click here for a tutorial on accessing the data). How can the NOAA CLASS output be displayed? This post will compare McIDAS-V plots to the data displayed using AWIPS-1, below.

GOES Sounder Total Column Ozone DPI Values Plotted with NAM 500-mb heights and NAM Pressure on the 1.5 PVU surface (click to enlarge)

GOES Sounder Total Column Ozone DPI Values Plotted with NAM 500-mb heights and NAM Pressure on the 1.5 PVU surface (click to enlarge)

Suomi NPP overflew the central United States at about 0850 UTC on 12 November, and ozone concentrations from the NUCAPS soundings at three different levels (~500, 300 and ~200 mb) are shown below. Note that the color scaling is not quite the same in the three plots as the range for each pressure level is different. Maxima in Ozone at all levels occur in the same region — the Dakotas — as indicated by the GOES Sounder Total Column Ozone DPI, above. NUCAPS soundings also show data in cloudy regions because microwave data from ATMS is used in the NUCAPS processing. Note that values at the edge of the color shading have been extrapolated outwards; values in western Nevada and Indiana, for example, are not from direct NUCAPS observations. This plot of 500-mb temperatures (that includes the actual values) shows the horizontal extent of data and the amount of interpolation at the edge.

Contours of Ozone Mixing Ratio (parts per billion) from NUCAPS Soundings at ~0848 UTC on 12 November 2014 (click to enlarge)

Contours of Ozone Mixing Ratio (parts per billion) from NUCAPS Soundings at ~0848 UTC on 12 November 2014 (click to enlarge)