Moist air over the tropical western Pacific Ocean

July 22nd, 2021 |
MIMIC Total Precipitable Water, 0000 UTC 21 July – 1200 UTC 22 July

Microwave estimates of total precipitable water over the western Pacific Ocean (available here) show a moist airmass — out of which Typhoon In-Fa (seen near Taiwan in the animation) emerged — over the western Pacific Ocean. (The circulation of Tropical cyclone Cempaka is also apparent near the Gulf of Tonkin) This rich moisture has led to very heavy rains and Flash Flood alerts on the island of Guam (at 13.4ºN, 144.5ºE). Are there any indications that a new tropical cyclone will emerge out of the moisture?

The toggle below shows Himawari-8 10.41 µm “Clean Window” infrared imagery (notice In-Fa in the northwest part of the image). A distinct trough is apparent in the scatterometery north of the Marianas islands (and north of 20ºN latitude), with west-southwesterly surface winds bordered by east-southeasterlies to the north. Weaker winds are indicated south of Guam. (For a recent primer on Scatterometer winds, click here; ASCAT winds can be found online here)

ASCAT Scatterometry winds and Himawari-8 Band 13 infrared (10.41 µm)imagery, 1200 UTC on 22 July 2021

NOAA-20 overflew this region at 1600 UTC on 22 July. The imagery below shows Tropopause Heights as well as Total Precipitable water — along with Band 13 imagery (over a different location) at that time. NUCAPS estimates of TPW are in the 60-70 mm range (in agreement with the MIMIC animation above); Very high tropopauses are Equatorward of 20 N Latitude.

A ribbon of small wind shear exists, as shown in the 200-850 wind shear analysis below, taken from the CIMSS Tropical Website. Meteorologists continue to monitor this region of tropical activity.

200-850 mb wind shear, 1800 UTC on 22 July 2021, over the western Pacific Ocean.

Aerosol Optical Depth and surface visibility

July 22nd, 2021 |
GOES-16 Aerosol Optical Depth and GOES-16 Band 2 Visible (0.64 µm) imagery, 1401 UTC on 22 July 2021

The image above shows the Level 2 GOES-R product, Aerosol Optical Depth (AOD), a product created in clear skies, overlain with the GOES-16 Visible imagery from the same time. AOD measures the extinction of light via scattering and absorption by small particles in the atmosphere, and it can be used as a proxy for particles smaller than 2.5 µm in diameter (PM25). The red regions show the highest values. The plot below shows surface observations of ceilings (plotted to the left of the circles) and visibility (plotted below the circles) at the same time as the AOD image above. Is there a relationship?

Look at the string of lower visibilities stretching along the North Carolina/South Carolina border, extending westward to Tennessee and then northward into Illinois. This is the region where AOD exceeds about 0.4 — cyan in the enhancement used above. In this instance, AOD can be used to highlight regions where surface visibilities are most restricted by aerosols. (Some of these aerosols are likely from smoke. However, this product does not tell you what kind of aerosol is there, only that it is causing extinction).

Surface observations of ceilings and visibilities, 1401 UTC on 22 July 2021

The toggle below steps through the observations, AOD, and Visible imagery at 1401 UTC. Kudos to Frank Alsheimer, the Science and Operations Office (SOO) in Columbia SC, for alerting us to this case.

Surface observations of ceilings and visibilities, GOES-16 Aerosol Optical Depth and GOES-16 Band 2 Visible (0.64 µm) imagery, 1401 UTC on 22 July 2021

True-color imagery, below, (saved in this case from the CSPP Geosphere site, using this link) also shows the extent of the aerosol-rich air.

GOES-16 ‘True-Color’ imagery at 1401 UTC on 22 July 2021

The relationship between AOD values and surface visibility persisted on 23 July 2021, below.

GOES-16 Aerosol Optical Depth and GOES-16 Band 2 Visible (0.64 µm) imagery, 1201 UTC on 23 July 2021