An anomalously-deep Hurricane Force low (surface analyses) moved eastward across the southern Bering Sea and eastern Aleutian Islands on 28 October 2022. GOES-18 (GOES-West) Air Mass RGB images (above) included plots of hourly surface reports — which showed some of the strong winds produced by this storm. Peak wind gusts included 75 knots / 86 mph at Dutch Harbor (PADU, at 0309 UTC on 29 October), 68 knots / 78 mph at Akutan (PAUT, at 0455 UTC on 29 October), 61 knots / 70 mph at St. George (PAPB, at 2140 UTC on 28 October, as heavy snow was being reported), 59  knots / 68 mph at Atka (PAAK, at 1645 UTC on 28 October) and 58 knots / 67 mph at Buoy 46073 (at 2200 UTC on 28 October). The 75 knot / 86 mph gust at Dutch Harbor and the 68 knot / 78 mph gust at Akutan occurred around the time that anomalously-strong 925 hPa winds were moving south-southeastward across the eastern Aleutian Islands (along the western and southwestern edge of the low pressure center).

The orange-to-red hues seen in the Air Mass RGB imagery indicated the presence of dry, ozone-rich stratospheric air within the upper portion of the atmospheric column (due to a lowering tropopause) — and AK-NAM40 model fields (below) suggested that the “dynamic tropopause” (taken to be the pressure of the PV1.5 surface) descended to the 600-675 hPa pressure level just south of the low pressure center.

Gridded NUCAPS Tropopause Height (derived using Metop-B and Metop-C CrIS/ATMS data) from the NASA SPoRT site (below) showed a narrow corridor of tropopause pressures near 600 hPa (brighter red enhancement) over and just north of the eastern Aleutians at 2108 and 2200 UTC — in general agreement with the AK-NAM40 model fields.

On the 1800 UTC Air Mass RGB image, a northwest-to-southeast oriented cross section line (Baseline B-B’) was positioned through the area of highest PV1.5 pressure values (above). The Baseline B-B’ cross section of model wind speed, potential vorticity and specific humidity (below) displayed a tropopause fold, as the dry air and high potential vorticity characteristic of stratospheric air descended southeastward around the upper-tropospheric 140-knot jet streak axis.

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A sequence of GOES-16 (GOES-East) Nighttime Microphysics RGB and Day Snow-Fog RGB images (above) showed the nocturnal development of lake effect fog/stratus plumes (lighter shades of yellow), which drifted northward from Lake Sakakawea in northwestern North Dakota on 26 October 2022. Two of the fog/stratus features moved across the Tioga and Stanley areas, where surface reports briefly indicated a drop in surface visibility to zero along with freezing fog. After sunrise, Day Snow-Fog RGB images revealed the dissipation of these lake effect fog/stratus features — and also displayed the areal coverage of early-season snow cover (shades of red) across the Montana/North Dakota border region.

The GOES-16 Nighttime Microphysics RGB image at 1001 UTC (below) includes an overlay of NOAA-20 VIIRS Sea Surface Temperature (SST) — the southerly flow of cold air (in the 20s F) across Lake Sakakawea’s SST values of 50-54ºF (shades of cyan) helped to create the lake effect fog/stratus features.

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Himawari-9 is slated to become operational (replacing Himawari-8, which has been operational at 140.7^o E Longitude since 2015!) on 13 December 2022 (Link). One change that users might observe arises from the slightly shorter central wavelength in the shortwave infrared band (Band 7). On Himawari-8, the central wavelength is 3.885 µm; on Himawari-9, the central wavelength is closer to 3.829 µm (see this link from JMA, or this one). The effect of the shorter wavelength on Himawari-9 is more noticeable during the daytime, when solar reflectance will lead to warmer observed brightness temperatures, especially over highly reflective convective updrafts (This presentation — see slide 19 — given at the CIRA RGB Workshop in October 2022, suggests daytime differences of up to 5 C.), and especially when compared to longwave infrared imagery as a brightness temperature difference.

The toggle above compares Himawari-8 visible imagery and Day Convection RGB imagery from Himawari-8 and -9 at 0200 UTC on 26 October 2022. in a region near Guam, without much intense convection. Subtle differences in the yellow shading over some convection are apparent (here’s a toggle just between Himawari-8 and -9 Day Convection RGB over Guam). It’s very hard to discern a difference in regions of no convection.

For strong convection, however, as shown below for a case over the south-central Equatorial Pacific, differences in yellow coloring over very strong convection are noteable; users might need to adjust the range of the RGB to draw out details in cloud tops, where, for Himawari-9 imagery, contrast is lost. (Here’s a toggle, over the strong convection, between Day Convection RGBs from Himawari-8 and Himawari-9).

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Spectral Response Functions for the infrared channels are available from Himawari-8 (here) and Himawari-9 (here). You will note that most infrared channels have similar functions; the outlier is band 7, shown below (and in this animated gif).

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Thanks to JMA for providing simultaneous image files for the different bands on Himawari-8 and Himawari-9!

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and Day Cloud Phase Distinction RGB images (above) showed the compact exposed low-level circulation of Tropical Invest 94L as it moved northward away from Bermuda (station identifier TXKF) on 25 October 2022. In spite of Invest 94L moving through an environment of increasing deep-layer wind shear, bursts of deep convection did develop near the center of the disturbance around 17 UTC (with the convection just to the northeast eventually producing GLM-detected lightning activity for about an hour). The system was also moving across relatively cool water, with Sea Surface Temperature values of around 25ºC just north of Bermuda.

At the time that the lightning activity first began, the GOES-16 Day Cloud Phase Distinction RGB image at 1751 UTC which includes cursor output values of Cloud Top Height, Cloud Top Phase and RGB components is shown below. The coldest cloud-top infrared brightness temperature of -73ºC occurred about 24 minutes later, as the convective burst was producing an overshooting top at 1815 UTC.

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