Blowing dust in Argentina

November 24th, 2021 |

GOES-16 “Red” Visible (0.64 µm), Dust RGB and Split Cloud Top Phase (11.2 µm – 8.4 µm) BTD images [click to play animated GIF | MP4]

30-second Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm), Dust RGB and Split Cloud Top Phase (11.2 µm – 8.4 µm) brightness temperature difference (BTD) images (above) revealed a plume of blowing dust propagating northward across the San Juan Province of western Argentina late in the day on 24 November 2021. The dust was being channeled through a gap in higher terrain along the foothills of the Andes (below).

GOES-16 “Red” Visible (0.64 µm) and topography images [click to enlarge]

A larger-scale view of hourly GOES-16 Visible images with plots of surface reports (below) suggested that this dust occurred in the vicinity of a strong cold front that was moving northward across Argentina.

GOES-16 “Red” Visible (0.64 µm) images, with METAR surface reports plotted in cyan [click to enlarge]

Mendoza — located south-southwest of where the dust plume first became apparent in GOES-16 imagery — reported a thunderstorm with dust at 2000 UTC (along with a southeasterly wind gust to 32 knots), followed by a reduction of surface visibility to 0.5 miles at 2215 UTC as the air temperature sharply dropped with the cold frontal passage (below). About 260 miles (420 km) east of Mendoza at Rio Cuarto, a similar sharp temperature drop was seen as the cold front passed.

Time series of surface data at Mendoza, Argentina [click to enlarge]

Showers over the south Pacific

November 24th, 2021 |
GOES-17 ABI Band 13 (“Clean Window”) Infrared (10.3 µm) imagery, 0000 – 1440 UTC on 24 November 2021 (Click to enlarge)

GOES-17 Infrared imagery, above, centered on American Samoa, shows several low-level cloud lines from which showers are developing (and then rapidly dying, suggestive of strong shear, as noted in this 0600 UTC shear analysis taken from this website). There are also convective elements developing over/near some of the islands. What is the moisture/stability distribution around these showers?

GOES-17 Total Precipitable Water fields, below, show American Samoa at the edge of a moist (TPW exceeding 2″) band (associated with the South Pacific Convergence Zone), dryer air (TPW is around 1.2″) to the northeast and relatively dry air to the south (TPW is around 1.3-1.4″ in patches). There is an increasing amount of noise in this Level 2 product starting around 1200 UTC, manifest as horizontal lines, that arise because of the poor functioning of the GOES-17 Loop Heat Pipe. As the ABI instrument’s focal plane’s temperature increases, bands that are used in the computation of Total Precipitable Water (including Band 15), become noisy. (Note that Band 13 on this day is not obviously affected by the increase in the focal plane temperature).

Hourly estimates of Total Precipitable Water, a cloud-free Level 2 GOES-17 product, displayed on top of GOES-17 clean window (Band 13, 10.3 µm) infrared imagery, 0000 to 1400 UTC on 24 November (Click to enlarge)

GOES-17 ABI data can also be used to estimate atmospheric stability, as shown below. Lifted Index fields (also showing Loop Heat Pipe-related striping at the end of the animation) show strongest instability in the region where showers are most common to the north of American Samoa — in the moist band. The strongest instability is over the southwestern part of this domain (the diagnosed Lifted Index there is near -5). Level 2 products from GOES-17 can give hints as to where convection will form out over the open ocean where conventional observations are sparse, even when Loop Heat Pipe issues with GOES-17 start to become obvious.

GOES-17 Lifted Index, a cloud-free Level 2 Product, plotted on top of GOES-17 Clean Window Imagery (Band 13, 10.3 µm), hourly from 0000 – 1400 UTC on 24 November 2021 (Click to enlarge)

Special note for the Lifted Index animation above: The bounds of the Lifted Index values have been changed from the AWIPS default — -10 to 20 — to -5 to 7; this was done to better differentiate between small variations in stability.

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.

Satellite signatures of the DART Mission launch

November 24th, 2021 |

GOES-17 Near-Infrared, Shortwave Infrared and Water Vapor images [click to play animated GIF | MP4]

1-minute Mesoscale Domain Sector GOES-17 (GOES-West) Near-Infrared “Snow/Ice” (1.61 µm). Near-Infrared “Cloud Particle Size” (2.24 µm), Shortwave Infrared (3.9 µm), Low-level (7.3 µm). Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) showed signatures of the DART Mission from Vandenberg Space Force Base in southern California on 24 November 2021. Shortly after the 0620 UTC launch, a warm thermal signature of the SpaceX Falcon 9 booster appeared in all 6 of these ABI spectral bands. Note that there were two 0621 UTC images; the 06:21:17 image was from the GOES-17 CONUS Sector — which, because it was scanning a much larger area, didn’t actually scan the rocket plume until around 06:21:57 UTC (the GOES-17 Mesoscale Sector 1 was scanning the rocket plume about 2 seconds earlier, at 06:21:55 UTC).

The corresponding GOES-17 Visible (spectral bands 1 and 2) and Near-Infrared (spectral bands 3-6) images are shown below. Since the satellite was viewing the rocket from the west, a very faint reflectance signature of the Falcon 9 booster could be seen in the first 3 post-launch 0.64 µm (Band 2) Visible images — but no discernible signature was evident in the lower-resolution 0.47 µm (Band 1) Visible imagery.

GOES-17 Visible and Near-Infrared images [click to play animated GIF | MP4]