Comparisons of LIS and GLM Lightning observations

May 4th, 2022 |
GOES-16 5-minute Flash Extent Density (updated every minute) and ISS LIS Flash Events, 1318-1320 UTC on 4 May 2022 (Click to enlarge)

The Geostationary Lightning Mapper (GLM) on GOES-16 and the Lightning Imaging Sensor (LIS, additional information here) on the International Space Station (ISS) both observe lightning. The GLM has nadir resolution of approximately 8 km, and is in geostationary orbit, about 36000 km above the Earth’s surface. In contrast, the LIS has a resolution of approximately 4 km, and it’s on the ISS, only 400 km above the Earth’s surface. Both sensors detect the optical signal of the lightning. The animation above shows 2 minutes of LIS Flash Events plotted (in yellow) on top of 5-minute aggregates of GLM Flash Extent Density (updated at 1-minute time-steps). The animation below shows the same LIS observations, but plotted in black, on top of GOES-16 ABI Band 13 imagery. Many of the LIS flash events are colocated with cold cloud top as defined by the GOES-16 Band 13 (10.3 µm) brightness temperatures — meaning that the optical signal is strongest there. That’s not always the case though, as shown in this image with LIS data from 13:19:48.

GOES-16 Band 13 Infrared (10.3 µm) imagery and LIS Flash Events, 1318-1320 UTC on 4 May 2022 (Click to enlarge)

Polar Hyperspectral Soundings and High Plains Convection

April 29th, 2022 |
PHSnMWnABI CAPE estimates, 1700 UTC 28 April to 0300 UTC 29 April 2022 (Click to enlarge)

On 28 April, SPC’s convective outlook showed a small region of SLGT RSK over western Nebraska, with Marginal probabilities over most of Nebraska and Kansas (link to 2000 UTC outlook). The animation above shows hourly CAPE predictions from a 3-km version of the Rapid Refresh that is run hourly and initialized with Polar Hyperspectral Data (infrared and microwave, from Metop and from Suomi-NPP and NOAA-20) fused with GOES-16 ABI data, thereby using the strengths of ABI (fine spatial and temporal resolution) and Polar Hyperspectral Soundings (excellent spectral resolution). The animation above (a mix of initial fields — 1700 – 1900 UTC ; 1 – 4h forecasts from 1900 UTC; and 6-9h forecasts from 1800 UTC) shows CAPE developing over the High Plains and then rotating north into Kansas by 0300 UTC on 29 April 2022. A later forecast of CAPE, below, runs from 2100 UTC 28 April through 0600 UTC 29 April (showing initial fields at 2100/2200 UTC, then forecasts from 2200 UTC at 2300 UTC through 0400 UTC [i.e., 1-6h forecasts], followed by 8h and 9h forecasts from 2100 UTC on 0500 and 0600 UTC). By 0600 UTC, an axis of instability stretches from western Nebraska southeastward into central Kansas. The two forecasts show similar patterns.

PHSnMWnABI CAPE estimates, 2100 UTC 28 April to 0600 UTC 29 April 2022 (Click to enlarge)

The toggle below compares two forecasts for 0300 UTC, a 9-h forecast from 1800 UTC on 28 April, and a 5-h forecast from 2200 UTC on 28 April. The 5-h forecast is a bit less quick in moving the high CAPE values northward.

5-h and 9-h forecasts valid at 0300 UTC on 29 April 2022 (click to enlarge)

So, what happened? The toggle below compares the 6-h forecast from 2200 UTC, valid at 0400 UTC on 29 April, with the initial field for the 0400 UTC model run. As above, it appears that the forecast model from 2200 UTC was a bit too fast in moving the CAPE northward and eastward into Kansas/Nebraska. But overall there is very good agreement between the two fields.

PHSaABI CAPE at 0400 UTC 29 April 2022: a 6-h forecast from 2200 UTC 28 April 2022, and the initial field for the 0400 UTC model run (Click to enlarge)

The animation below shows PHSnABI CAPE fields hourly from 0400 – 0700 UTC (initial fields from 0400-0600; 1-h forecast at 0700), side by side with observed GOES-16 ABI Band 13 color-enhanced brightness temperatures. The convection that develops is along the edges of the CAPE; that is, it forms along the CAPE gradient in the model. Click here to view SPC Storm Reports from 28-29 April.

PHSnABI CAPE values, 0400-0700 UTC (left) and GOES-16 ABI Band 13 infrared (10.3 µm) imagery, 0401-0701 UTC 29 April 2022 (click to enlarge)

The animation below shows ABI Infrared Imagery overlain on top of the forecast CAPE field. This drives home to point that convection on this day occurred where the gradient of CAPE was outlined/predicted by this forecast model.

PHSnABI CAPE fields overlain with GOES-16 Infrared ABI Band 13 (10.3 µm) imagery, 0800-1200 UTC on 29 April 2022 (Click to enlarge)

PHSnABI data will be demonstrated at the Hazardous Weather Testbed in late May/Early June. Model output is available outside of AWIPS at this website. To view more blog posts on this project, click the ‘Hyperspectral’ tag below.

Satellite detection of ice

February 25th, 2022 |

A colder-than-normal February over the western Great Lakes (through the 27th, Duluth is 10o F below normal; Marquette is 5o F below normal; Green Day is 2o F below normal; Cleveland is 1o F below normal) has fostered a growth in ice cover over the Lakes (This figure, from here, for example). How can satellites detect that ice, especially for a region where winter-time cloudiness is notorious? In general, there are two different ways to detect ice: Visible/Infrared imagery and Microwave imagery. The toggle above shows Advanced Technology Microwave Sounder (ATMS) ice detection (using MiRS algorithms and data from Suomi-NPP (1807 UTC) and NOAA-20 (1859 UTC)) over the Great Lakes on 25 February 2022. (These data come from the Direct Broadcast antenna at CIMSS, and are processed using CSPP to produce AWIPS-ready tiles that are available via an LDM feed). A big challenge with this field is the very large ATMS footprint. Note that these sea-ice concentration values are quantitative: values change based on how much ice is within the footprint but are also dependent on view angle.

VIIRS data (as shown at the VIIRS Today website, for example) can also be used to infer regions of ice in a qualitative sense, as shown below. The true color imagery shows possible ice features over the lakes. It’s a challenge, however, to use a single VIIRS image to distinguish (mostly) stationary ice from (usually) moving clouds. Multispectral VIIRS imagery means (via the use below of the 2.25 µm M11 band) ice features are cyan colored and can be qualitatively distinguished from clouds. Consider, for example, the color difference in the False Color image between the clouds over eastern Lake Superior (white in both True- and False-Color) and near-shore ice over southern and eastern Lake Superior (white in the True-Color and cyan in the False-Color). There are also VIIRS-based Ice Concentration products that can be computed in clear skies.

Suomi-NPP VIIRS True- and False-Color imagery over the Great Lakes, 1806 UTC on 25 February 2022 (Click to enlarge)

For cloudy regions, Advanced Baseline Imagery can be used to create estimates of Ice Surface Temperature and Ice Concentration. Quantitative estimates such as these give more information than the qualitative estimates shown above. These estimates at present are only created hourly; in partly-cloudy regions, that cadence is sufficient to give lake-wide quantitative estimates of ice coverage and temperature. CONUS imagery — with a 5-minute time cadence — and mesoscale sectors — with 1-minute cadences — can be used to monitor (in a qualitative sense) how ice is moving (as shown link, for example). High temporal-resolution imagery is important because ice sheets can change rapidly under strong winds, as shown in this tweet. At high latitudes, there are also ways of monitoring ice motion via polar orbiters (link).

GOES-16 Estimates of Ice Surface Temperatures, 1800 and 1900 UTC on 25 February 2022 (Click to enlarge)
GOES-16 Estimates of Ice Concentration, 1800 and 1900 UTC on 25 February 2022 (Click to enlarge)

A much higher-resolution method of viewing ice (again, in a qualitative, not quantitative sense) in regions of both clear and cloudy skies, day or night, is through the use of Synthetic Aperture Radar (SAR). Data are available for each Great Lake at this link. Imagery for each Lake over the past days is available there, albeit infrequently (usually around 0000 and 1200 UTC only) and over small domains. This qualitative imagery, however, is very high-resolution and gives very impressive details. Imagery over Lake Erie is shown below.

RCM estimates of Lake Erie Ice, 24-27 February 2022 (Click to — greatly! — enlarge)

VIIRS and ABI give both qualitative (false-color, visible imagery) and quantitative (ice concentration and ice temperature) depictions of ice over the lakes — or over coastal waters around Alaska. Microwave data also gives quantitative estimates (ice concentrations with large microwave footprints) and qualitative estimates (SAR data). Use all products to create a clear picture of ice coverage.

Cyclone Batsirai in the southern Indian Ocean

February 1st, 2022 |
MIMIC Total Precipitable Water estimates, 2100 UTC 31 January – 2000 UTC 1 February 2022 (click to enlarge)

MIMIC Total Precipitable Water esimates over the Indian Ocean for the 24 hours ending at 2000 UTC on 1 February 2022, above, show the strong cyclonic circulation associated with Cyclone Basirai. Its forecast motion is westward towards Madagascar, as shown in the toggle below that also includes sea-surface temperatures and Window Channel (showing a well-structured storm; all images are from the SSEC/CIMSS Tropical Website). A wind shear analysis (also from the SSEC Tropical Website and valid at 1800 UTC on 1 February) for the Indian Ocean shows low shear values over the storm, but relatively high shear between the storm and the island of Madagascar.

Forecast Path for Batsirai, sea-surface temperature analysis, and window channel satellite imagery, times as indicated (Click to enlarge)

Batsirai’s path moves it close to Mozambique/Malawi, two countries that are still being flooded as a result of rains from Tropical Storm Ana a week ago. A VIIRS flood analysis (from this website), below, diagnoses active flooding occurring along the Shire River (south of Lake Malawi) and along the Zambezi River on 31 January 2022.

River Flood Analysis from VIIRS imagery, 5-day composite endings 31 January 2022 (click to enlarge)

For more information on Batsirai, consult the RSMC at La Réunion (click ici) or the SSEC Tropical Website.