Gravity Waves forced by an isolated thunderstorm in the Gulf of Mexico

April 9th, 2018 |

GOES-16 ABI Upper-Level Water Vapor (6.2 µm) Infrared Imagery, 1352-1857 UTC on 9 April 2018 (Click to animate)

Upper-level Water Vapor (6.2 µm) infrared imagery on 9 April 2018 (above) revealed gravity waves propagating away from an isolated thunderstorm in the Gulf of Mexico.

The convective complex generated gravity waves that were visible in all 3 GOES-16 ABI Water Vapor Channels (6.19 µm, 6.95 µm and 7.34 µm).  The image below (produced using SIFT, the Satellite Information Familiarization Tool and data from NOAA CLASS) shows all three channels at 1812 UTC;  the color enhancement used is the same in each image, but the ranges were modified to make the gravity waves most visible.  Ranges used were -109 to 34 º C (Band 8); -109 to 55 º C (Band 9) and -80 to 42 º C (Band 10).

Weighting functions for the three water vapor infrared channels for three stations surrounding the Gulf of Mexico (Slidell, LA; Tallahassee FL; Tampa FL) suggest the gravity waves were in the 300-450 mb layer (6.2 µm) to the 450-600 mb layer (7.3 µm).

GOES-16 ABI Water Vapor Infrared Imagery at 1812 UTC on 9 April 2018: Upper Level (left), Mid-Level (center), Low-Level (right) (Click to enlarge)

GOES-16 ABI Legacy Profiles and Suomi NPP NUCAPS Profiles in AWIPS

April 8th, 2018 |

NUCAPS Sounding Availability points plotted over a VIIRS Visible (0.64 µm) image at 1815 UTC, 8 April 2018 (click to enlarge); NUCAPS Soundings from the point nearest Miami and Key West are shown below

NUCAPS vertical profile near Key West FL, 18Z on 8 April 2018 (Click to enlarge)

NUCAPS vertical profile near Miami FL, 18Z on 8 April 2018 (Click to enlarge)

NUCAPS (NOAA-Unique Combined Atmospheric Processing System) vertical profiles have been available in AWIPS for some time now (Click here to see how to access them in AWIPS; they are also available online at this site). Legacy Atmospheric Profiles (LAP) derived from ABI Channels (and GFS Information) are available in AWIPS now as well (horizontal fields derived from LAP soundings are available online as well). How do Legacy Atmospheric Profiles compare to NUCAPS profiles? Both are derived from satellite data. (Click here for a Quick Guide on NUCAPS; Click here for a Quick Guide on Legacy Atmospheric Profiles).

The strength of NUCAPS Soundings is that they are observation-based and independent of a model first guess (or background field). That is, they are retrieved from satellite measurements of emitted radiation at hundreds of different wavelengths in the infrared and in the microwave, with a statistical regression as first guess. In the case of NUCAPS from Suomi NPP (or NOAA-20), the data are from CrIS and from ATMS, infrared and microwave sounders, respectively. Compare the vertical profiles above to the 12 UTC soundings from Miami and Key West. There is better vertical resolution in the radiosondes, of course, but NUCAPS provides timely model-independent information at times when convective initiation might be starting.

NUCAPS Soundings Availability (plotted on top of the VIIRS 11.45 µm infrared image from 1815 UTC), a subset of GOES-16 LAP Sounding Availability points (plotted on top of the GOES-16 0.64 µm Visible Image), and then all GOES-16 LAP Sounding Availability points (Click to enlarge)

NUCAPS Soundings are produced in clear and partly cloudy conditions. This owes to the 3×3 CrIS field of regard that is incorporated into each NUCAPS profile, and to the ability of microwave imagery to produce a sounding in cloudy (but not precipitating) regions.

In contrast, LAP temperature and moisture profiles are produced only where the GOES-16 Clear Sky Mask identifies clear skies. LAP output is on a 10-km grid, however, so there are many possible soundings. The image below, zoomed in over southern Florida, shows in cyan the availability of LAP Vertical Profiles, and the availability in NUCAPS Soundings, color-coded Green, Yellow and Red (the meaning of the points is described in the Quick Guide). There are many LAP points, but they do not exist anywhere where clouds are present. The LAP grid is the same from one time to the next however.

GOES-16 ABI Visible (0.64 µm) Imagery at 1752 UTC, LAP locations at 1752 UTC (cyan points) and NUCAPS Sounding availablilty points (Green, Yellow, Red points) at 1758 UTC (Click to enlarge)

Because LAP are produced every 30 minutes at the CONUS scale, at the same point each time, their evolution can tell you something. Note, however: these profiles are very heavily constrained by the GFS (Global Forecasting System) 1/2-degree simulation that is used to create LAP information. That is, they are not independent of the model (as is the case for NUCAPS Vertical Profiles). GOES-R ABI tells very little about the temperature structure of the atmosphere in particular because it lacks the spectral resolution of, for example, the GOES-15 Sounder that has multiple channels around 4.4 µm and multiple channels around 14 µm. The GOES-R Series of satellites does not include a hyperspectral sounder such as CrIS (on Suomi-NPP and NOAA-20) or IASI (on Metop-A and Metop-B).

GOES-R ABI does have similar moisture information as the GOES-15 Sounder — both have 3 separate water vapor channels making observations between 6 µm and 7.5 µm. Thus, the Legacy profiles might alter the moisture in the vertical profiles from the GFS, but it is far less likely that GOES-16 ABI will cause a notable change in temperature profiles from the GFS. In contrast, as noted above, NUCAPS Vertical Profiles are satellite observations only created via a regression and a retrieval that uses as a tool a Radiative Transfer Model.

Thus, when you see a time animation of a series of LAP soundings, as shown below, you are likely seeing the evolution of the GFS vertical profiles with a modest change in mid-level moisture occurring because of GOES-16 ABI data. Note also that soundings will not be produced when the clear-sky mask indicates clouds. Thus, the sounding near Key West shows hourly values from 09 to 21 UTC (with some gaps); the sounding near Miami for the same time-span shows hourly values only at 13, 15 and 16 UTC — because more clouds are present. Changes in the LAP sounding temperature are likely the result of GFS information changing; changes in LAP moisture are from both GFS moisture changing and/or GOES ABI water vapor channel information changing.

GOES-16 LAP Vertical Profiles of Temperature and Moisture at from 09-21 UTC for a point near Key West (Click to enlarge)

GOES-16 LAP Vertical Profiles of Temperature and Moisture at 13, 15 and 16 UTC for a point near Miami (Click to enlarge)

LAP data are used to create Derived Stability Indices (CAPE, Total Totals, Lifted Index, K-index, Showalter Index) and Total Precipitable Water. These integrated quantities, also available in AWIPS, are likely to be more useful to forecasters than point data. This is especially true because the most reliable information from the LAP Soundings and the derived stability indices are gradients and time tendencies. (Here is an animation of Lifted Index from 1332 – 2147 UTC on 8 April 2018)

In 2019, AWIPS will included gridded horizontal fields derived from NUCAPS temperature and moisture profiles. This will allow visualization of convective parameters such as Lifted Index and CAPE. In addition, NUCAPS soundings from NOAA-20 and from Metop-A and Metop-B will flow to AWIPS at some point after early Summer 2018, greatly increasing the number of observation-based soundings available.

GOES-16 ABI RGB product artifacts related to Keep Out Zones

April 6th, 2018 |

GOES-16 ABI Full Disk Imagery at 0430 UTC on 6 April. Bands 8 (6.19 µm), 10 (7.34 µm), 12 (9.6 µm) and 13 (10.3 µm) are shown (Click to enlarge)

GOES-16 ABI Full Disk Imagery at 0530 UTC on 6 April. Bands 8 (6.19 µm), 10 (7.34 µm), 12 (9.6 µm) and 13 (10.3 µm) are shown (Click to enlarge)

Eclipse season for GOES-16 occurs around the Equinoxes when the satellite can enters the Earth’s shadow. Long ago (before GOES-12), Eclipse Season meant the satellite lost power because the solar array that powers the satellite was in a shadow. GOES-16 has batteries that allow it to function when solar power is missing. However, as the satellite emerges from the Earth’s shadow, the Advanced Baseline Imager can point too close to the Sun, so portions of the image are not scanned and sent to the receiving station. The two animations above step through four different channels on ABI (Band 8 (6.19 µm), Band 10 (7.34 µm), Band 12 (9.6 µm) and Band 13 (10.3 µm), at 0430 UTC, when the Keep-Out Zone (KOZ, sometimes called the Cookie Monster effect) is northwest of the subsatellite point, and at 0530 UTC, (also Band 8 (6.19 µm), Band 10 (7.34 µm), Band 12 (9.6 µm) and Band 13 (10.3 µm)) when the KOZ is northeast of the subsatellite point.  Note in particular that the size of the KOZ is different with different channels.

If Channel Differences are used in a product, this intra-band size difference of the KOZ has an affect.  The toggle below shows the Airmass RGB (Red Component:  Split Water Vapor (6.19 µm – 7.34 µm) ; Green Component: Split Ozone, (9.6 µm – 10.3 µm); Blue Component: 6.19 µm) at 0430 UTC and 0530 UTC on 6 April 2018.  At 0430 UTC, there is a region where only the blue part of the Airmass RGB (from the 6.19 µm band) is present;  at 0530 UTC, the Keep-Out Zone border shows only magenta (i.e., a lack of Green) because the Split Ozone Channel (9.6 µm – 10.3 µm) is missing there.

AIrMass RGB (defined in Text) at 0430 and 0530 UTC on 6 April 2018 (Click to enlarge)

NOAA’s Office of Satellite and Product Operations (OSPO) maintains a website that describes Eclipses and Keep Out Zones.

Surface Cold Front over the High Plains of Texas

April 3rd, 2018 |

Hourly GOES-16 ABI Low-Level Water Vapor Infrared (7.34 µm) Imagery, and hourly observations, 0700-1600 UTC on 3 April 2018 (Click to enlarge)

A cold front moving southward along the western Great Plains showed a distinct signature in GOES-16 Water Vapor Imagery.  The hourly animation above, with surface observations, shows the front in the Low-Level Water Vapor passing over stations where winds shift from westerly and southwesterly to strong northerly.  The feature is far more trackable in GOES-16 ABI Imagery with a 5-minute cadence as is typical over CONUS, as shown below for both low-level water vapor infrared imagery (Band 10, 7.34 µm) and upper-level water vapor infrared imagery (Band 8, 6.19 µm). The infrared imagery allowed a precise determination of when the cold front would reach a location. (In fact, because a GOES-16 Mesoscale Sector was placed over west Texas, the time of arrival could be observed down to the minute, as shown in this animation of the clean window (10.3 µm) infrared imagery from GOES-16).

GOES-16 ABI Low-Level Water Vapor Infrared Imagery (7.34 µm), 0832-1637 UTC on 3 April 2018 (Click to animate)

GOES-16 ABI Upper-Level Water Vapor Infrared Imagery (6.19 µm), 0832-1637 UTC on 3 April 2018 (Click to animate)

Visible Imagery after sunrise (below) shows that some surface cloudiness was associated with this feature — but other parts were clear.

GOES-16 ABI “Red” Visible Imagery (0.64 µm), 1252-1637 UTC on 3 April 2018 (Click to animate)

It is not common for surface features to appear in the Upper-Level Water Vapor Imagery, even when the surface is near 900 mb, as over the High Plains of west Texas. Weighting Functions show from which layers in the atmosphere energy detected by the satellite originates. The Weighting function from Amarillo TX at 1200 UTC on 3 April is shown below.  The low-level water vapor weighting function — shown in magenta — shows contributions from the surface, but the upper-level water vapor weighting function — shown in green, shows contributions ending about 200 mb above the surface, at around 700 mb.  A conclusion might be that the depth of the cold air quickly increases to around 200 mb behind the front.  Thus is can appear in the Upper-Level water vapor imagery.   The cold front passes Amarillo (here is a meteorogram) shortly before 1200 UTC (and before the Radiosonde was launched).  The radiosonde from Dodge City Kansas, however, at 1200 UTC, shows a cold layer about 200 mb thick.  (Here is the Amarillo Sounding for the same time;  it’s shown in the Weighting Function plot below as well).

Clear-Sky Weighting Functions from Amarillo TX, 1200 UTC on 3 April 2018 (Click to enlarge)

Interpretation of water vapor imagery is simplified if you use information from weighting functions to understand the three-dimensional aspect of the water vapor imagery.