NUCAPS soundings near a Tropical Disturbance

July 1st, 2014 |
Suomi/NPP 11.35 µm infrared channel, 0717 UTC on 1 July 2014 and NUCAPS sounding locations in green (click to enlarge)

Suomi/NPP 11.35 µm infrared channel, 0717 UTC on 1 July 2014 and NUCAPS sounding locations in green (click to enlarge)

Suomi/NPP overflew the developing tropical depression #1 (now Tropical Storm Arthur) east of Florida early in the morning on July 1st. The CrIS and ATMS instruments on board S/NPP provide data for NUCAPS soundings that are routinely distributed to AWIPS II. The image above is an overlay of the 11.35 µm infrared imagery with the sounding locations plotted as green dots. Seven sounding locations are indicated on the image above (Here is the image without the seven sounding locations) How well do NUCAPS soundings represent the tropical atmosphere that is supporting the development of Arthur?

The 7 soundings indicated in the plot above are: 1 (Just south of Pensacola, FL), 2 (Off the coast of Georgia), 3 (northeast of Arthur in the tropical Atlantic), 4 (Cape Canaveral), 5 (north of Tampa Bay), 6 (the western tip of Cuba) and 7 (northeastern Cuba).

GOES Sounder DPI Total Precipitable Water at 0700 UTC on 1 July 2014 (click to enlarge)

GOES Sounder DPI Total Precipitable Water at 0700 UTC on 1 July 2014 (click to enlarge)

How does Precipitable Water from the NUCAPS soundings compare to observations from other satellite-based systems? GOES Sounder DPI TPW from 0800 UTC shows values around 50 mm over interior the southeast United States, and over the tropical Atlantic to the northeast of the tropical system. A corridor of lower values, around 30-35 mm, extends northeast of Jacksonville, FL. Smaller values (30-40 mm) also extend southeastward from the lower Mississippi River valley into the Gulf of Mexico. A similar pattern in the precipitable water is evident in the blended product, here. Precipitable water values from the NUCAPS soundings appear, for this case, to be too low. The value at Cape Canaveral (point 4), for example, is 1.59″ (40 mm, versus close to 50 mm from the Sounder and the Blended Product); off the coast of Georgia (point 2), 1.30″ (33 mm vs. close to 41 mm from the Sounder and Blended Product); south of Pensacola (point 1), 1.25″ (31 mm vs. 35 mm from the Sounder and the Blended Product); north of Tampa Bay (point 5), 1.46″ (37 mm vs 47 mm from the Sounder and the Blended Product); northeast of the tropical system (point 3), 1.84″ (47 mm vs 49 mm from the Sounder/Blended Product); western Cuba (point 6), 1.70″ (43 mm, similar to the 44 mm from the Sounder/Blended Product); and northeast cuba (point 7), 1.22″ (31 mm vs. 39 from the Sounder and 34 from the Blended Product). The lowest 3 kilometers of the atmosphere (where most of the moisture resides) is the most difficult part for a satellite-based sounding, but there do appear to be differences between the two satellite-based sounding products (GOES and NUCAPS) in this case.

NUCAPS Soundings available in AWIPS II

June 10th, 2014 |
Suomi/NPP VIIRS 11.45 µm IR channel and NUCAPS sounding points (click to enlarge)

Suomi/NPP VIIRS 11.45 µm IR channel and NUCAPS sounding points (click to enlarge)

NOAA Unique Cross-track Infrared Sounder (CrIS)/Advanced Technology Microwave Sounder (ATMS) Processing System (NUCAPS) Soundings have started flowing into AWIPS-2 at NWS WFOs across the country. These soundings offer high spectral (and high spatial) resolution soundings derived from the CrIS and ATMS instruments that fly on the Suomi/NPP satellite. The toggle above shows the footprint of the soundings in comparison to an 11.45 µm VIIRS instrument (also on the Suomi/NPP satellite) IR image from approximately 1800 UTC on 10 June 2014. The NUCAPS soundings cover a larger area because they are processed by NOAA/NESIS (vs. being downloaded on the X-Band Direct Broadcast antenna at CIMSS in Madison WI, whose antenna is the source of the VIIRS 11.45 µm IR image shown).

The sounding data, if available, are under the ‘Satellite’ menu tab of AWIPS-2, and then NPP Products can be selected to view NUCAPS Sounding Availability, as shown in this screenshot. Once the sounding locations are loaded, the mouse can be used to select a point, and a left click produces a sounding in an NSharpEditor environment; that is, you can edit it (if, for example, you think the surface dewpoint in the sounding is too dry).

The mid-continent overpass at around 1800 UTC can provide valuable information on the possibility of convective development. For example, consider the visible imagery below from 1915 UTC on May 29 2014. Will convection develop out of that broken cumulus field as forecast by the GFS (not shown)?

GOES-13 0.63 µm Visible Imagery, 1915 UTC 29 May 2014 (click to enlarge)

GOES-13 0.63 µm Visible Imagery, 1915 UTC 29 May 2014 (click to enlarge)

The animation below steps through the Suomi/NPP overpass just after 1800 UTC that was used to created NUCAPS soundings on that day, followed by a close-up over Omaha, then a screen-capture of the created sounding. The sounding (which includes surface values close to those reported by the METAR) has only modest values of Convective Available Potential Energy (CAPE), suggesting that convection is unlikely. And, indeed, visible imagery near sunset shows dissipating cumulus clouds.

NUCAPS Sounding over North America, over Omaha and surroundings, and the individual NUCAPS sounding indicated (Courtesy of Dan Nietfeld, SOO at Omaha/Valley WFO, click to enlarge)

NUCAPS Sounding over North America, over Omaha and surroundings, and the individual NUCAPS sounding indicated (Courtesy of Dan Nietfeld, SOO at Omaha/Valley WFO, click to enlarge)

A second case, below, also from Dan Nietfeld, shows NUCAPS soundings before the devastating hailstorm on June 3 in a High Risk region. In this case, the NUCAPS soundings underestimated the temperature/dewpoint at the surface, but the editable sounding software makes quick work of adjusting the lowest part of the sounding, and the CAPE in the adjusted sounding increased from 1800 to more than 3000. (The location of the sounding is shown here; it is the southern of the two circled green dots.) NUCAPS data underscores the potential of any convection.

NUCAPS soundings, original and adjusted, 1849 UTC on 3 June (click to enlarge)

NUCAPS soundings, original and adjusted, 1849 UTC on 3 June (click to enlarge)

(Click here for further information on ATMS; Click here for further information on CrIS). Many thanks to Dan Nietfeld, SOO at Omaha, for imagery above. Hyperspectral Soundings are described in a COMET module that can be viewed here. A paper (pdf format) describing validation of NUCAPS soundings is available here. Suomi/NPP support is provided in part by the NOAA/NESDIS Joint Polar Satellite System (JPSS) program.

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.

Sequential NUCAPS Profiles at Higher Latitudes

October 20th, 2016 |

Suomi NPP Day/Night Band (0.70 µm) and NUCAPS Sounding Locations, 0538 and 0724 UTC on 20 October 2016. Green Dots represent soundings that have passed quality control; Yellow Dots represent soundings for which the infrared retrieval failed; Red dots represent soundings for which both infrared and microwave retrievals failed (Click to enlarge)

The orbital geometry of Suomi NPP is such that regions north of about 43º N latitude can occasionally receive NUCAPS (NOAA-Unique Combined Atmospheric Processing System) Vertical Profiles of moisture and temperature on sequential orbital passes, meaning a given location could have vertical profiles separated by less than 2 hours. This occurred early on 20 October 2016 over Maine and Cape Cod, as shown above: Suomi NPP NUCAPS Vertical Profile locations are indicated over Day/Night Band Visible imagery. Two soundings at approximately the same location are circled in cyan in this small image and are shown below. There are two sequential profiles over Cape Cod, and then the two sequential profiles north of Maine. The atmosphere over Cape Cod was quiescent on this date, and little change between soundings is evident. In contrast, slight cold air advection was occurring north of Maine (Surface analysis from 0900 UTC, 500-mb analysis from 00 UTC), and the NUCAPS Sounding shows mid-level cooling.


NSharp depictions of NUCAPS Vertical Profiles near 42N, 70W at 0500 and 0700 UTC on 20 October 2016 (Click to enlarge)


NSharp Depictions of NUCAPS Vertical Profiles near 48 N, 68 W at 0500 and 0700 UTC on 20 October 2016 (Click to enlarge)

For stations in the northern Plains, or in Canada, sequential soundings overnight or perhaps more importantly in the mid-afternoon (Suomi NPP typically overflies the Plains a bit after Noon local time) could give important information about destabilization.

Previous CIMSS Satellite Blog Entries referencing NUCAPS Vertical Profiles are available here.

=============== Added 2100 UTC on 20 October 2016 ===============
The toggle below shows two soundings, from 1700 and 1800 UTC in central Pennsylvania in the region between Harrisburg and Williamsport (click here to see the Sounding Locations), just east of a slight risk issued by the Storm Prediction Center. The time evolution suggests upward motion (the top of the inversion rises) and a weakening in the cap. Severe Thunderstorm Watch #499 was issued 1945 UTC on 20 October for counties just to the west of these NUCAPS Profile locations — and damaging winds were reported in central Pennsylvania beginning at 2154 UTC.

NSharp depictions of NUCAPS Vertical Profiles near 41N, 77W at 1700 and 1800 UTC on 20 October 2016 (Click to enlarge)