NUCAPS use over Alaska

November 24th, 2021 |
NOAA-20 NUCAPS Sounding Availability Points, 0953, 1132 and 1310 UTC on 24 November 2021; the 1132 UTC imagery also shows 500-mb plots from 1200 UTC Radiosondes. (Click to enlarge)

A useful strength of NUCAPS profiles over Alaska is that at that northern Latitude, sequential overpasses will overlap so that one location will be sampled sequential times. In the example above, note for example that portions of Canada’s Northwest Territories are sampled three times. Much of southern Alaska is sampled twice. Thus, NUCAPS profiles there allow a user to ascertain routinely how the atmosphere is changing over 90 minutes, usually at times surrounding radiosonde observations at 1200 UTC (and 0000 UTC).

The animation below shows NUCAPS soundings and the upper air sounding at CYVQ (Norman Wells) in the Northwest Territories, at the edge of the Sounding Availability Plots imagery above. There is warming between the two NUCAPS profiles, and gross aspects of the NUCAPS and radiosonde profiles agree (for example: Tropopause Height, low-level inversion). Always remember that a NUCAPS profile is representative of a volume of air; radiosondes sample individual points as they ascend.

NUCAPS Profiles near Normal Wells, NWT, at 1000 and 1121 UTC, and the 1200 UTC CYVQ Upper Air sounding (click to enlarge)

The plots below compare the 1200 UTC PAFC (Anchorage AK) soundings with nearby NUCAPS soundings. General agreement here is better: Tropopause heights are similar, a low-level inversion is present, as is general drying with height. Note how the sequence of PAFC sounding and the two NUCAPS soundings show a slow lower-tropospheric warming trend.

The 1200 UTC PAFC (Anchorage AK) soundings, and two NUCAPS Profiles near Anchorage, at 1132 and 1301 UTC (click to enlarge)

Use the daily overlap of NUCAPS soundings to give yourself a twice-daily estimate of how the troposphere is changing over Alaska. Gridded NUCAPS fields (not shown) will also overlap and can also be used in this way. NUCAPS are an observational product that is largely independent of model data.

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