MIRS Ice Concentration Products over the Great Lakes

January 20th, 2020 |

MIRS Lake Ice Concentration (as a percentage) from NOAA-20 ATMS at 0735 UTC on 19 January 2020 (Click to enlarge)

CIMSS is now providing via LDM MIRS Lake Ice Products over the Great Lakes. These data are created using the Community Satellite Processing Package (CSPP) Software and NOAA-20/Suomi-NPP ATMS data downlinked at the Direct Broadcast Antennas in Madison WI. Imagery is shown above from 0735 UTC on 19 January 2020; the image below is from 0717 UTC on 20 January 2020, from NOAA-20, about 24 hours later, and then from 0808 UTC on 20 January 2020, from Suomi NPP (although it is labeled as NOAA-20). A great benefit of these microwave products is that they are not affected by persistent cloud cover that is common over the Great Lakes in winter.

MIRS Lake Ice Concentration (as a percentage) from NOAA-20 ATMS at 0717 UTC on 20 January 2020 (Click to enlarge)

MIRS Lake Ice Concentration (as a percentage) from NOAA-20 ATMS at 0806 UTC on 20 January 2020 (Click to enlarge)

Ice concentration estimates from microwave are very strongly influenced by view angle. Make certain in your comparisons (if you are trying to ascertain changes in lake ice coverage during Lake-Effect Snow events, for example) that you understand this! If the footprint sizes are similar, a comparison to different passes is valid; if the footprint sizes differ, the effects of view angle must be considered. Orbital paths can be viewed here (NOAA-20 it passed right over Lake Erie at 0722 UTC on 20 January; Suomi-NPP passed over Duluth at 0812 UTC on 20 January). In the two examples above, note how ice cover estimates differ over Lake Ontario. In the later example, from ATMS on Suomi-NPP, Lake Ontario is far closer to the limb; the ATMS footprint is much larger and the estimate of lake ice concentration is affected. This toggle compares the VIIRS Day Night band image to the ATMS observations; Lake Ontario is close to the limb for NPP’s pass over western Lake Superior at this time.

For instructions on how to access these data, please contact the blogpost author. Many thanks to Kathy Strabala and Lee Cronce, CIMSS, for their work in making these data available. Click here for short video explaining MIRS Ice Concentration).

Added: A consequence of the relatively poor resolution of ATMS (compared to, say, AMSR-2 on GCOM) is that a footprint in the Great Lakes will often not be over only water or over only land. A mixed surface (land and water within the ATMS footprint) means that the ice concentration algorithm will struggle to interpret the signal and reach the right solution. Best resolution from ATMS occurs near the sub-satellite point (from 15-50 km, depending on the frequency), and that’s where this product give the best information. (Thanks to Chris Grassotti, NOAA/CISESS for this information)

Can you use NUCAPS soundings to determine the rain/snow line?

January 9th, 2020 |

NUCAPS Horizontal Temperature field, 925 hPa, at 1704 UTC on 9 January 2020, toggled with NUCAPS sounding observation points from the same orbit (Click to enlarge)

NOAA-Unique Combined Atmospheric Processing System vertical profiles of moisture and temperature are derived from retrievals that consider both infrared sounder data (from the Cross-track Infrared Sounder, CrIS) and microwave sounder data (from the Advanced Technology Microwave Sounder, ATMS). In AWIPS, the profiles are from NOAA-20 but they are also produced with data from Suomi-NPP. NUCAPS profiles from NOAA-20 and Suomi-NPP are available here (the site also includes NUCAPS profiles from MetOp satellites; those NUCAPS profiles use IASI infrared and MHS microwave data).

Polar2Grid software can be used to create horizontal fields of thermodynamic information from the vertical profiles (as discussed here). For the National Weather Service forecast offices, an extra step is taken that interpolates (in the vertical) the NUCAPS data from the pressure levels in the Radiative Transfer Model that is used in the retrievals to standard pressure levels. The toggle above compares the vertical profile points at 1648 UTC on 9 January 2020 to the  925-hPa temperature field. Note that derived field does extend outwards from the outermost NUCAPS profile: the sphere of influence for an individual NUCAPS point can be adjusted.  Note that the bounds of the temperature field have been adjusted from AWIPS defaults, and the color table has been modified so that 0º C occurs between the green and cyan values.  (A more intuitive color table for rain-snow discernment would include more color gradations in the -5º C to +5º C range).  Where the low-level thermal gradient occurs should help a forecaster determine where rain is more likely and where snow is more likely.

Dewpoint Depression at 925 hPa, 1704 UTC on 9 January 2020 (Click to enlarge)

Moisture fields are available as well at thermal fields.  Thus, the effects of evaporation might be considered.  The image above shows the dewpoint depression at 925 hPa.  Lapse rates derived from NUCAPS are also available (the one below shows the temperature change from 850 to 500 hPa). If strong vertical motion is forecast, the lapse rate and/or the dewpoint depressions fields can help you anticipate how much cooling might occur.

850-500 mb Lapse Rate, 1704 UTC on 9 January 2020 (Click to enlarge)

Note that horizontal fields as presented in NUCAPS include data from all NUCAPS profiles, thereby including points that may be ‘green’ (the infrared and microwave retrievals both converge to solutions), ‘yellow’ (the infrared retrieval failed, but the microwave retrieval converged) and ‘red’ (neither retrieval converged). It’s incumbent on the analyst to consider the impact of those profiles where convergence to a solution did not occur when using these fields.

(Thanks to Christopher Stumpf, WFO MKX, for assistance in getting these images)

Using GEOKOMPSAT-2 and Himawari-8 Imagery to create Stereoscopic Imagery

November 14th, 2019 |

Visible (0.64 µm) Imagery from Himawari-8 (left) and GEOKOMPSAT-2A (right) at 0400 and 0500 UTC on 14 Nov 2019 (Click to enlarge)

Geostationary data from KMA‘s GEOKOMPSAT-2 satellite (over the Equator at 128º E Longitude, shown above at right) and from JMA‘s Himawari-8 Satellite (over the Equator at 140º E Longitude, shown above at left) can be used to create stereoscopic imagery. The imagery above, from 0400 and 0500 UTC on 14 November 2019, centered at 15º N, 150º E, shows Typhoon Fengshen. Visible imagery from both satellites show a well-developed central cluster of thunderstorms with little apparent indication of wind shear. Stereoscopic views of the storm allow the vertical structure of the system to be perceived.

Data processing for these images was accomplished using Geo2Grid, a software package that incorporates Satpy. (Previous Blog posts discussing Geo2Grid are here and here).

Very grateful acknowledgement of these data from KMA and from JMA is extended. Thank you!

Added:  Click here for an animation from 0300 to 0550 UTC on 14 November.  (Warning:  Large animated gif at 159 M).

Gridded NUCAPS in AWIPS, part II

November 12th, 2019 |

NUCAPS horizontal plots of 850-hPa temperature, 1643-1705 UTC on 12 November 2019, and the NUCAPS Sounding Availability plots (Click to enlarge)

As noted in this post from October, horizontal fields of thermodynamic variables that have been derived from NUCAPS vertical profiles are now available in AWIPS. The fields give a swath of observations derived from infrared and microwave sounders in regions of the troposphere where observations by Radiosondes happen only occasionally. In this case, NUCAPS observed the strong cold front moving southward into the north Atlantic. Temperatures over eastern Canada at 850 hPa were in the teens below 0 Celsius, and in the teens (Celsius) out over the Atlantic.

850-hPa Temperatures derived from NUCAPS Soundings, 1653 UTC on 12 November 2019 (Click to enlarge)

Lower-tropospheric temperatures are an important variable to know when early-season cold airmasses are cold enough that the temperature difference between 850 hPa and surface water bodies — such as rivers and lakes — is sufficient to support Lake (or River) Effect clouds and precipitation. River-effect flurries hit mid-town Memphis on the 12th of November, and the 0.86 “Veggie” image (0.86 µm, this wavelength was chosen because land/water contrasts are large in it) image, below, shows a band extending from the Mississippi River in northwest Tennessee southward into central Memphis. NUCAPS data at 850 on this day showed 850-mb temperatures around -10 C at 0900 UTC.

GOES-16 0.86 “Veggie” Band (0.86 µm) imagery, 1346 UTC on 12 November 2019 (Click to enlarge). Shelby County in Tennessee is outlined, and the arrow points to a River-Effect snow band that dropped flurries over mid-town Memphis.