NUCAPS moisture and cloud fields over the central Pacific Ocean

March 2nd, 2021 |

GOES-17 Visible Imagery (0.64 µm), 2310 UTC on 2 March 2021, along with gridded values of NUCAPS Temperature and Relative Humidity (both averaged between (850-700 mb) at 2306 UTC on 2 March 2021 (Click to enlarge)

NOAA-Unique Combined Atmospheric Processing System (NUCAPS) data from CrIS and ATMS on NOAA-20 can give temperature and moisture information in regions otherwise lacking data. How well do those fields estimate the actual distribution of temperature and moisture? The toggle above compared visible imagery with gridded fields of temperature and moisture from NUCAPS from late in the day on 2 March 2021.

The thermal fields depict the frontal zone far to the south of Hawaii;  cooler air where shallow cumulus convection is occurring is farther north.  Of particular note is the excellent spatial correspondence between diagnosed dry air around and just to the northeast of Hawaii and an obvious lack of cloudiness there!  (Here is the 0000 UTC 3 March 2021 sounding from Hilo; a strong inversion is just below 700 mb.)

Using NUCAPS lapse rates to evaluate atmospheric stability

February 26th, 2021 |

GOES-17 Visible Imagery (2300 UTC), NOAA-20 NUCAPS-derived lapse rate (925 – 700 mb, 23:03 UTC) and NUCAPS sounding points (2249 UTC) on 25 February 2021 (Click to enlarge)

NUCAPS profiles derived from CrIS and ATMS data on NOAA-20 provide model-independent estimates of atmospheric thermodynamics globally, including, for this case over the central Pacific Ocean, in regions otherwise bereft of data.  NUCAPS lapse rates show a minimum in stability in low-levels in between two cloud features; the region includes mostly ‘green’ NUCAPS retrieval points:  where infrared and microwave retrievals have both converged.  It is difficult in the case above to relate differences in cloud features to differences in the diagnosed stability.

Four minutes later (shown below), NOAA-20 was closer to the Pole on this ascending pass and the diagnosed stability does relate well to differences in cloud structures.  In particular, the change from lapse rates around 5 C/km northeast of Hawai’i to lapse rate closer to 2 or 3 C/km even farther northeast aligns with a boundary between cloud types.

GOES-17 Visible Imagery (2310 UTC), NOAA-20 NUCAPS-derived lapse rate (925 – 700 mb, 23:07 UTC) and NUCAPS sounding points (2249 UTC) on 25 February 2021 (Click to enlarge)

The subsequent NOAA-20 pass was west of the main Hawai’ian Island chain.  Again, differences in lapse rates are related to cloud features in the visible imagery.  Stable air — with lapse rates between 3 and 4 C/km — overlies a region of very little cumuliform development.  A region of larger lapse rates over the eastern 1/3rd of the pass, just to the west of the Hawai’ian Islands is accompanied by cumulus development.  NUCAPS thermodynamic fields, even though they have limited resolution in the vertical (at most 10 layers in the enter tropopause), can give useful information on stability over the ocean that can help in the real-time diagnosis of the atmosphere.

NUCAPS fields across an upper tropospheric front

January 20th, 2021 |

GOES-16 ABI Airmass RGB, Band 10 and Band 8 (7.34 µm and 6.19 µm, respectively), and GOES-16 Airmass RGB overlain with NUCAPS sounding availability plots, 0801 UTC oni 20 January 2021 (click to enlarge)

The AirMass RGB from GOES-16 at 0800 UTC on 20 January 2021 showed a distinct color change across central Missouri, from red to green.  The enhanced red coloring suggests a large difference in water vapor brightness temperatures.  The toggle above (including an image with NUCAPS* sounding points), shows structures in the water vapor imagery consistent with an upper tropospheric front.

Water Vapor and Airmass RGB imagery fields are useful because they be compared to model fields of the tropopause, and similarities in model fields and satellite imagery lend credence to the idea that the model initialization is accurate.  Compare the Airmass RGB and the Rapid Refresh mapping of the pressure on the 1.5 PVU surface below.  There is good spatial correlation between model and satellite fields.

GOES-16 Airmass RGB and Rapid Refresh model field of Pressure on the 1.5 PVU surface, 0800 UTC 20 January 2021 (Click to enlarge)

How do vertical profiles from NUCAPS vary across the tropopause fold?  The animation below shows six different profile in Missouri and Arkansas, spanning the reddish region of the airmass RGB.

GOES-16 Airmass RGB image with selected NUCAPS profiles, as indicated. (Click to enlarge)

A more efficient way to view information from NUCAPS is to view gridded fields.  Polar2Grid is used to transform the vertical profile to horizontal fields at the individual NUCAPS pressure levels (and then vertical interpolation moves those fields to standard levels).  The animations below show gridded values that are all in agreement with the presence of a tropopause fold where the Airmass RGB and model fields suggest.  Gridded temperature and moisture can be combined in many ways.  Gridded Ozone is also available in AWIPS (some of these fields were created using the Product Browser).

Ozone from NUCAPS, below, does show an enhancement, as expected, in the region where the tropopause fold is suggested by the airmass RGB.

NUCAPS-derived ozone anomalies, ca. 0800 UTC on 20 January 2021 (Click to enlarge)

The gridded NUCAPS tropopause level, shown below, can also be inferred from the individual profiles shown above.

Gridded NUCAPS Tropopause level, ca. 0800 UTC on 20 January 2021 (click to enlarge)

Note how the lapse rates show relatively less stable air (in the mid-troposphere) in the region of the tropopause fold.

Gridded 500-700 mb Lapse rates, ca. 0800 UTC on 20 January 2021 (click to enlarge)

Mixing ratio shows dry mid- and upper-tropospheric air, in the region of the tropopause fold, as might be expected from the GOES-16 water vapor imagery.

Gridded NUCAPS esimates of 300-700 mb mixing ratio, ca. 0800 UTC on 20 January 2021 (Click to enlarge)

In general, NUCAPS data can be used to augment other satellite and model data to better understand the thermodynamic structure of the atmosphere.  For more information on NUCAPS profiles, refer to this training video.

*The careful reader will note that the timestamp of the NUCAPS Sounding Availability plot, 0753 UTC, is different from the GOES-16 imagery.  Why?  The NUCAPS Sounding Availability plot is timestamped (approximately) when NOAA-20 initially overflies North American airspace.  NOAA-20 was flying over Missouri shortly after 0800 UTC, as shown in this plot (from this website).  Gridded NUCAPS fields are timestamped when NOAA-20 is overhead.

Comparing NUCAPS temperature values to forecast fields

November 29th, 2020 |

Gridded NUCAPS estimates of 850-mb Temperature, 1851 UTC on 30 November 2020 (Click to enlarge)

Late November is a time when cold outbreaks can pass over relatively warm Great Lakes waters (click here for recent observations) and produce lake-effect snow. Gridded NUCAPS observations derived from NOAA-20 CrIS and ATMS data, above, shows a large area with temperatures colder than -12ºC over northwest Ontario and northern Minnesota, just upwind of the Great Lakes;  Lake Superior’s surface temperature at the time was around 5ºC —  a temperature difference that support lake-effect precipitation.  How well do the NUCAPS observations compare to model predictions of the environment?

Forecasts from the 1200 UTC run of the NAM, below, valid at 1800 UTC, and from the 1500 UTC run of the Rapid Refresh, valid at 1900 UTC, show -12ºC in bright magenta.  (Model analyses taken from this website)  NUCAPS analyses suggest the cold air is moving south faster than anticipated by the model.


6-h forecast of 850-mb Temperature, valid 1800 UTC on 29 November 2020 (Click to enlarge)

4-hour forecast of 850-mb temperature from the Rapid Refresh, valid 1900 UTC on 29 November 2020 (Click to enlarge)

This site can be used to view gridded NUCAPS fields outside of AWIPS.  The 850-mb analysis from the pass is shown below.  It’s important to recall that Gridded NUCAPS fields include data from all retrieved profiles — including profiles for which the infrared retrieval failed (usually in locations with thick clouds, and those from which the infrared and microwave retrievals both failed (usually in locations with rain). This mapping for the temperature gridding below shows where infrared retrievals failed (yellow) and where infrared and microwave retrievals both failed (red).

850-mb Temperature fields, 1849 UTC on 29 November 2020 (Click to enlarge)

The ‘yellow’ points north and west of the Great Lakes were associated with clouds that are apparent in this VIIRS True Color image, taken from the UW-Madison Direct Broadcast ftp site (Link). The clouds were associated with a departing low pressure system (link).

NOAA-20 VIIRS True-Color imagery, 1850 UTC on 29 November 2020 (Click to enlarge)