Comparing Gridded NUCAPS data to model fields

February 24th, 2020 |

NUCAPS fields of 850-mb dewpoint Temperature toggled with NAM40 and RAP40 estimates at approximately the same time, ~1800 UTC on 24 February 2020 (Click to enlarge)

Gridded NUCAPS fields include 850-mb dewpoint temperature fields, and this blog post compares the NUCAPS fields to model fields, and this is part of an ongoing series of blog posts on these horizontal fields.  The imagery above compares NUCAPS fields at 850 mb with NAM40 and RAP40 data over the southeastern part of the United States.  Very dry air is indicated over the western Atlantic Ocean north and west of the Gulf Stream.  There is generally good agreement between the NUCAPS and model fields. Model fields appear dryer (or NUCAPS fields are more moist).  Model fields show a pronounced gradient over the upper midwest that, at this scan time, were too far west to be viewed by NUCAPS.  (Click here to view the NUCAPS points — green, yellow and red — for this time, to show something about the data that has been input into the gridded fields).

However, the following pass from NOAA-20 (click here to view NOAA-20 orbit paths) included midwestern data.  Again, the general good agreement is obvious, especially with regard to the placement of the gradient. Is the atmosphere as dry as the model suggests at 850 mb? That’s a hard question to answer given 1200 UTC Soundings at Omaha, Minneapolis/Chanhassen, and Green Bay.  Note that NAM12 and RAP13 data are being shown in this example;  they gave mostly the same answer as NAM40/RAP40 used above.

NUCAPS fields of 850-mb dewpoint Temperature toggled with NAM12 and RAP13 estimates at approximately the same time, ~1900 UTC on 24 February 2020 (Click to enlarge)

Gridded NUCAPS over the southeast United States

February 21st, 2020 |

Analyzed snow depth at 0600 UTC on 21 February 2020 from the NOHRSC (Click to enlarge)

Snow fell over the southeastern United States, principally North and South Carolina, late on 20 February/early on 21 February 2020. This blog post, one in a series, investigates how gridded NUCAPS thermal fields perform in analyzing the rain/snow line. The snow totals are shown above, an image that was taken from this website at the National Operational Hydrologic Remote Sensing Center (NOHRSC).

NOAA-20 overflew the Carolinas shortly after 0700 UTC on 21 February, and gridded values of 950-mb, 900-mb and 850-mb Temperatures are shown below. (Note how the 950-mb field intersects the ground at the western edge of the Piedmont).  The 0º C isotherm at 850 and 900 mb is close to the coast;  it is sub-freezing over most of the land at those levels.  The analysis from 950-mb shows cold air stretching southwestward from southeastern Virginia, and that region is also where the accumulating snow was focused.  This is an argument in favor of the temperature fields in NUCAPS giving useful information about the rain/snow line.

850-mb, 900-mb, and 950-mb analyses of temperature derived from NUCAPS vertical profiles of temperature, 0723 UTC on 21 February 2020. The same color enhancement is used for each level, spanning -40º C to 30º C; 0º C is highlighted by the black line (Click to enlarge)

One of the gridded NUCAPS fields available in AWIPS via the Product Browser (there are many!) is the binary probability of a temperature occurring.  The 850-mb binary probability of 0º C is close to the coast, at 900-mb, just slightly inland.  The 950-mb values also suggest cold air is more likely over the region where snow fell.  There are also some embedded cold pockets at 950 mb over interior North/South Carolina.

Conditional Probability of 0 C at 850, 900 and 950 mb, 0723 UTC on 21 February 2020 (Click to enlarge)

Note that gridded NUCAPS fields include data from infrared retrievals, microwave-only retrievals, and from retrievals that do not converge. The gridding can mask behavior in the vertical profiles that might not necessarily engender confidence in a meteorological analyst. The plot below shows NUCAPS points (Green points are infrared retrievals that successfully converged, yellow points are microwave-only retrievals, and red points occur where the microwave-only and infrared retrievals failed to converge; this is typically where precipitation is falling) plotted on top of the 850-mb temperature analysis.  Note, however, that values do show up everywhere!  Users of the gridded data should keep in mind the quality of the data that goes into the analysis when they use it.  Two vertical soundings from which gridded data are derived are shown at bottom.  Users can decide if they would use those vertical soundings in isolation.

850-mb Temperatures with NUCAPS Sounding points superimposed, 0711 UTC, 21 February 2020 (Click to enlarge)

850-mb Temperatures with NUCAPS Sounding points superimposed, 0711 UTC, 21 February 2020. Two soundings are also shown, from a green point and from a yellow point.  Note that the plot also shows the binary probability of a temperature at 0º C (Click to enlarge)

Can you use gridded NUCAPS fields to diagnose the rain/snow line?

February 13th, 2020 |

900-mb Temperature fields (color-shaded; the 0ºC line is in black) derived from NOAA-20 NUCAPS profiles, 0624 UTC on 13 February, along with 0600 UTC METAR observations (Click to enlarge)

Gridded NUCAPS fields include a wide range of thermodynamic variables. The plot above shows the 900-mb temperature field. Is it possible to use this data to diagnose a rain/snow transition line?

Over southern New England, the relationship between 900-mb temperatures and surface precipitation observations seems robust: snow is restricted to most (but not all!) places where 900-mb temperatures are cooler than 0ºC. and rain falls where temperatures exceed 0ºC. Where terrain might be an influence in trapping cold air near the surface — the Catskills, for example, or the Alleghenies over New York and Pennsylvania, the relationship is not so straightforward. This data source warrants future investigations on its utility in these situations.

Ozone Estimates from NUCAPS

February 11th, 2020 |

Gridded NUCAPS (from NOAA-20) estimates of total ozone concentration at 1643 and 1653 UTC 11 February 2020 (Click to enlarge)

Gridded NOAA-Unique Combined Atmospheric Processing System fields in AWIPS (and elsewhere, such as this excellent site) include retrieved values of ozone (O3), an important gas.  In high concentrations in the upper troposphere, O3 is a marker for the presence of stratospheric air.  In the animation above, high concentrations of ozone are present over eastern Canada.  An earlier pass, shown below in a toggle with GOES-16 ABI Band 13 (10.3 µm, the “clean window”) and with a 6-h forecast of pressure on the 1.5 PVU surface (the forecast from the UK Met Office Global Model) shows a cold enhancement on the poleward side of the cold front draped across the North Atlantic, and a southward tropospheric intrusion of the stratosphere as visualized by the higher pressure on the 1.5 PVU surface.  That is to say, there is a dynamic response in the atmosphere to the intrusion of stratospheric air (with higher ozone) into the troposphere.

GOES-16 ABI Band 13 (10.3 µm), NUCAPS Ozone (both at 1500 UTC 11 February), and Forecast Temperature on the 1.5 PVU Surface (at 1800 UTC) from the UKMet Office Global Model (Click to enlarge)

Can you use the Ozone Band — Band 12 on the ABI, at 9.61 µm, to estimate where high ozone concentrations exist in the atmosphere?  The short answer to this is “No” — at least if you’re using just the 9.61 µm band.  Compare the retrieved and gridded values below from NUCAPS with the Band 12 brightness temperature;  it is difficult to make a claim that this single ABI band gives useable information in the detection of ozone.

Gridded NUCAPS estimates of Ozone, and the Band 12 “Ozone” band (9.61 µm) at 1650 UTC on 11 February 2020 (Click to enlarge)

At later overpass, over the western United States, leads to a similar conclusion:  Gridded NUCAPS Ozone values can highlight lower tropopauses upstream of developing storms (in this case on 11 February, over the southwestern United States);  Band 12 Ozone fields do not highlight stratospheric intrusions.

Gridded NUCAPS estimates of Ozone, and the Band 12 “Ozone” band (9.61 µm) at 2005 UTC on 11 February 2020 (Click to enlarge)

Some other examples from 11 February: over Southwestern Canada (toggle from 2016 UTC, Gridded NUCAPS Ozone, ABI Band 12); over the central United States (toggle from 1829 UTC, Gridded NUCAPS OzoneABI Band 12).