Strong midlatitude cyclone north of Hawai’i

February 10th, 2019 |
GOES-17

GOES-17 “Red” Visible (0.64 µm) images [click to play MP4 animation]

* GOES-17 images shown here are preliminary and non-operational *

1-minute Mesoscale Domain Sector GOES-17 “Red” Visible (0.64 µm) images from the AOS site (above) showed the distinct circulation of a strong midlatitude cyclone (surface analyses) that was centered just north of Hawai’i on 10 February 2019. The pressure gradient associated with this storm produced strong winds across the island chain. Wave heights to 38.4 feet were recorded at Buoy 51208 near Kaua’i, with wind gusts to 57 knots at Buoy 51001 northwest of Kauwa’i.



GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (below) revealed the presence of numerous lee waves which extended hundreds of miles downwind of the islands — most notable were those emanating from Kauwa’i.

GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) images [click to play animation | MP4]

GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images [click to play animation | MP4]

Derived Motion Winds calculated using GOES-15 (GOES-West) Water Vapor (6.5 µm) imagery from the CIMSS Tropical Cyclones site (below) showed targets with velocites of 150-160 knots just north of Hawai’i at 09 UTC and 12 UTC.

Derived Motion Winds calculated using GOES-15 Water Vapor (6.5 µm) imagery [click to enlarge]

Derived Motion Winds calculated using GOES-15 Water Vapor (6.5 µm) imagery [click to enlarge]

GOES-17 Air Mass RGB images (below) showed the orange to red hues signifying a lowered tropopause and increased stratospheric ozone within the atmospheric column as the storm evolved during the 09-10 February time period.

GOES-17 Air Mass RGB images [click to play MP4 animation]

GOES-17 Air Mass RGB images [click to play MP4 animation]

Suomi NPP VIIRS True Color and Infrared Window (11.45 µm) images at 23 UTC as viewed using RealEarth are shown below.

Suomi NPP VIIRS True Color and Infrared Window (11.45 µm) images at 23 UTC [click to enlarge]

Suomi NPP VIIRS True Color and Infrared Window (11.45 µm) images at 23 UTC [click to enlarge]

Strong jet stream over the North Pacific Ocean

January 2nd, 2019 |
GOES-17 Mid-level Water Vapor (6.9 µm) images, with 250 hPa wind isotachs [click to play animation | MP4]

GOES-17 Mid-level Water Vapor (6.9 µm) images, with 250 hPa wind isotachs [click to play animation | MP4]

* GOES-17 images shown here are preliminary and non-operational *

GOES-17 Mid-level Water Vapor (6.9 µm) images with an overlay of 250 hPa wind isotachs from the GFS90 model (above) showed a string of disturbances (surface analysis) along the axis of a 180-knot “Japan Jet” across the North Pacific Ocean on 02 January 2019.

GOES-17 Split Ozone (9.6 µm10.3 µm) Brightness Temperature Difference images (below) include an overlay of PV1.5 pressure (an indicator of the height of the “dynamic tropopause”) — they showed the difference between cold polar air having a low tropopause (shades of cyan to blue) north of the jet stream and warm tropical air having a much higher tropopause (shades of yellow). The Split Ozone BTD is the Green component of the Air Mass Red-Green-Blue (RGB) product.

GOES-17 Split Ozone (9.6 - 10.3 µm) images, with contours of PV1.5 pressure [click to play animation | MP4]

GOES-17 Split Ozone (9.6 – 10.3 µm) images, with contours of PV1.5 pressure [click to play animation | MP4]

Rawinsonde data also showed the significant difference in tropopause height between St. Paul Island, Alaska (pressure=314 hPa, height=8.1 km) in the polar air of the Bering Sea and Lihue, Hawai’i (pressure=82 hPa, height=17.9 km) in the tropical air of the central Pacific (below).

Plots of rawinsonde data from St. Paul Island, Alaska [click to enlarge]

Plots of rawinsonde data from St. Paul Island, Alaska [click to enlarge]

Plots of rawinsonde data from Lihue, Hawai'i [click to enlarge]

Plots of rawinsonde data from Lihue, Hawai’i [click to enlarge]

GOES-17 Air Mass RGB images from the UW-AOS site (below) further illustrated the sharp contrast between the cold/dry polar air to the north and warm/moist tropical air to the south of the strong jet stream. The purple hues along the northwestern edge of the scan are a result of the “limb cooling” effect, as the satellite’s infrared detectors sense radiation from colder upper levels of the atmosphere at large viewing angles.

GOES-17 Air Mass RGB images [click to play animation | MP4]

GOES-17 Air Mass RGB images [click to play animation | MP4]

In addition to the series of larger disturbances along the jet stream axis, there were also some smaller-scale storms apparent in the Bering Sea (surface analyses). Better detail of these high-latitude features could be seen using Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images separated by 10 hours (below).

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 1427 UTC and 0022 UTC [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 1427 UTC and 0022 UTC [click to enlarge]

Regarding the strong Japan Jet, GOES-15 (GOES-West) Derived Motion Winds (source) tracked targets having velocities as high as 200 knots at 03 UTC (below).

GOES-15 Water Vapor (6.5 µm) Derived Motion Winds [click to enlarge]

GOES-15 Water Vapor (6.5 µm) Derived Motion Winds [click to enlarge]

Hurricane-Force low over the Aleutian Islands

December 29th, 2018 |
Water Vapor images from GOES-17 (6.9 µm, left) and GOES-15 (6.5 µm, right) [click to play animation | MP4]

Water Vapor images from GOES-17 (6.9 µm, left) and GOES-15 (6.5 µm, right) [click to play animation | MP4]

* GOES-17 images shown here are preliminary and non-operational *

A mid-latitude cyclone moved northward over the far western Aleutian Islands late in the day on 28 December 2018, intensifying to a Hurricane Force low pressure system by 06 UTC on 29 December (surface analyses). A comparison of GOES-17 and GOES-15 (GOES-West) Water Vapor images (above) highlighted the improved spatial resolution of the GOES-17 data (2 km at satellite sub-point, vs 4 km for GOES-15). The view from GOES-15 was more oblique, since it was positioned at 128º W longitude (compared to 137.2º W longitude for GOES-17). GOES-17 is scheduled to become the operational GOES-West satellite in January 2019.

A toggle between GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images at 1100 UTC is shown below. Although the satellite viewing angle was large, good detail could still be seen.

GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images at 1100 UTC [click to enlarge]

GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images at 1100 UTC [click to enlarge]

A sequence of Suomi NPP VIIRS Visible (0.64 µm), Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images (below) showed the storm as it was intensifying — the peak surface wind gust at Shemya Eareckson Air Station (PASY) was 66 knots at 1024 UTC. Since the Moon was in the Waning Gibbous phase (at 60% of Full), there was ample illumination to provide a useful “visible image at night” with the VIIRS Day/Night Band at 1403 UTC (4:03 AM local time).

Suomi NPP VIIRS Visible (0.64 µm), Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm), Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images [click to enlarge]

A time series plot of hourly surface weather data from Shemya during the time period of the GOES-17/15 Water Vapor image comparison is shown below, along with a more detailed time series that included Special Reports in addition to the standard Hourly Reports..

Time series plot of surface weather data from Shemya Eareckson Air Station [click to enlarge]

Time series plot of Hourly surface weather data from Shemya Eareckson Air Station [click to enlarge]

Time series plot of Hourly and Special surface weather data from Shemya Eareckson Air Station [click to enlarge]

Time series plot of Hourly and Special surface weather data from Shemya Eareckson Air Station [click to enlarge]

Train of standing waves south of Hawai’i

November 25th, 2018 |
GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images [click to play animation | MP4]

GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images [click to play animation | MP4]

* GOES-17 images shown here are preliminary and non-operational *

GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) revealed an interesting train of standing waves about 100-150 miles south of the Big Island of Hawai’i on 25 November 2018. With the presence of moisture aloft, the 3 water vapor weighting functions — calculated using the 00 UTC Hilo sounding — were shifted to high enough altitudes to eliminate the sensing of radiation from features in the lower troposphere. There were no pilot reports of turbulence in the vicinity of these standing waves — but they were located outside of the primary commercial air traffic corridors to/from the islands.

GOES-17 “Clean” Infrared Window (10.3 µm) and Near-Infrared “Cirrus” (1.37 µm) images (below) showed that these wave clouds were radiometrically transparent to longwave thermal energy being emitted from/near the surface — note that marine boundary layer stratocumulus clouds could be seen drifting westward within the easterly trade wind flow. As a result, the satellite-sensed 10.3 µm infrared brightness temperatures of the standing wave clouds were significantly warmer than that of the air at higher altitudes where they existed. These standing wave cloud features were, however, very apparent in 1.37 µm Cirrus imagery, along with what appeared to be other thin filaments of cirrus cascading southward overhead. The southward motion of the features seen on Cirrus imagery suggests that they existed at pressure levels of 370 hPa (26,900 feet / 8.2 km) or higher — altitudes where northerly winds were found on the Hilo sounding.

GOES-17 "Clean" Infrared Window (10.3 µm) and Near-Infrared "Cirrus" (1.37 µm) images [click to play animation | MP4]

GOES-17 “Clean” Infrared Window (10.3 µm) and Near-Infrared “Cirrus” (1.37 µm) images [click to play animation | MP4]

A comparison of all 16 ABI spectral bands is shown below. Note that in the longwave infrared bands along the bottom 4 panels, the brightness temperatures are progressively colder (darker shades of green) on the 11.2 µm, 12.3 µm and 13.3 µm images — each of these bands are increasingly affected by water vapor absorption aloft, therefore more effectively sensing the thin layer of higher-altitude standing wave clouds. AWIPS cursor sampling showed the differences in detected brightness temperature at 3 different points along the feature: here, here and here. The increasing sensitivity to radiation emitted from higher altitudes can also be seen in a comparison of weighting functions for ABI bands 13, 14, 15 and 16.

GOES-17 images of all 16 ABI bands [click to play animation | MP4]

GOES-17 images of all 16 ABI spectral bands [click to play animation | MP4]

GOES-15 (GOES-West) Water Vapor (6.5 µm), Infrared Window (10.7 µm) and Infrared CO2 (13.3 µm) images (below) showed that the lower spatial resolution of the legacy GOES Imager infrared bands (4 km at satellite sub-point) was not able to resolve the individual waves as well as the 2-km GOES-17 ABI images . Also, as was seen with the GOES-17 imagery, the 13.3 µm CO2 brightness temperatures of the standing wave clouds were significantly colder (shades of blue) compared to those of the conventional 10.7 µm Infrared Window. The corresponding GOES-15 Visible imagery (0.63 µm) is also available: animated GIF | MP4.

GOES-15 Water Vapor (6.5 µm, keft), Infrared Window (10.7 µm, center) and Infraered CO2 (13.3 µm, right) images [click to play animation | MP4]

GOES-15 Water Vapor (6.5 µm, keft), Infrared Window (10.7 µm, center) and Infraered CO2 (13.3 µm, right) images [click to play animation | MP4]

In comparisons of VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images from Suomi NPP and NOAA-20 visualized using RealEarth (below), note the highly-transparent nature of the standing wave clouds on the RGB images; only the earliest 2256 UTC VIIRS 11.45 µm image displayed brightness temperatures of -20ºC and colder (cyan to blue enhancement).

Suomi NPP VIIRS True Color RGB and Infrared Window (11.45 µm) images at 2256 UTC [click to enlarge]

Suomi NPP VIIRS True Color RGB and Infrared Window (11.45 µm) images at 2256 UTC [click to enlarge]

NOAA-20 VIIRS True Color RGB and Infrared Window (11.45 µm) images at 2336 UTC [click to enlarge]

NOAA-20 VIIRS True Color RGB and Infrared Window (11.45 µm) images at 2336 UTC [click to enlarge]

Suomi NPP VIIRS True Color RGB and Infrared Window (11.45 µm) images at 0028 UTC [click to enlarge]

Suomi NPP VIIRS True Color RGB and Infrared Window (11.45 µm) images at 0028 UTC [click to enlarge]

Terra (at 2043 UTC) and Aqua (at 2347 UTC) MODIS True Color RGB images along with retrievals of Cloud Phase, Cloud Top Temperature, Cloud Top Height and Cloud Top Pressure from the WorldView site (below) indicated that the standing wave feature was composed of ice crystal clouds exhibiting temperature values of -53ºC and colder (dark purple enhancement) located at heights of 12 km or higher (and at pressure levels at or above 250 hPa). These temperature/height/pressure values roughly corresponded to the upper portion of a layer of increasing relative humidity between 200-274 hPa on the Hilo sounding.

Terra MODIS True Color RGB image and retrievals of Cloud Phase, Cloud Top Temperature, Cloud Top Height and Cloud Top Pressure at 2043 UTC [click to enlarge]

Terra MODIS True Color RGB image and retrievals of Cloud Phase, Cloud Top Temperature, Cloud Top Height and Cloud Top Pressure at 2043 UTC [click to enlarge]

Aqua MODIS True Color RGB image and retrievals of Cloud Phase, Cloud Top Temperature, Cloud Top Height and Cloud Top Pressure at 2347 UTC [click to enlarge]

Aqua MODIS True Color RGB image and retrievals of Cloud Phase, Cloud Top Temperature, Cloud Top Height and Cloud Top Pressure at 2347 UTC [click to enlarge]

However, an experimental CLAVR-x version of GOES-17 Cloud Type, Cloud Top Temperature and Cloud Top Height products (below; courtesy of Steve Wanzong, CIMSS) indicated Cirrus clouds having temperature values in the 210-200 K (-63 to -73ºC) range at heights within the 13-16 km range. These colder/higher values raise the question of whether the wave clouds might have formed and been ducted within the shallow temperature inversion near 15 km on the Hilo sounding.

GOES-17 Cloud Type product [click to play animation | MP4]

GOES-17 Cloud Type product [click to play animation | MP4]

GOES-17 Cloud Top Temperature product [click to play animation | MP4]

GOES-17 Cloud Top Temperature product [click to play animation | MP4]

GOES-17 Cloud Top Height product [click to play animation | MP4]

GOES-17 Cloud Top Height product [click to play animation | MP4]

GOES-17 False Color RGB images (below) vividly portrayed the transparent nature of the high-altitude standing wave cloud feature, which allowed westward-moving stratocumulus clouds within the marine boundary layer to plainly be seen. The RGB components are 1.38 µm / 0.64 µm /  1.61 µm.

GOES-17 False Color RGB images [click to play animation | MP4]

GOES-17 False Color RGB images [click to play animation | MP4]

A coherent explanation of this feature and what caused it to form remains elusive, earning it a distinguished place in the what the heck is this? blog category. Perhaps one clue existed in the winds aloft, as depicted by the NAM at 200 hPa, 250 hPa and 300 hPa (below), which showed northerly/northeasterly flow that was decelerating as it entered a trough axis (the region within the red box). Could this flow deceleration have induced a “reverse flow” which then caused enough weak lift to form the thin standing wave clouds within the aforementioned semi-moist 200-274 hPa layer seen on the Hilo sounding? No other obvious forcing mechanisms were in the immediate area — a slowly-approaching surface cold front was too far north of Hawai’i to have played a role.

NAM Winds at 200 hPa, 250 hPa and 300 hPa [click to enlarge]

NAM Winds at 200 hPa, 250 hPa and 300 hPa [click to enlarge]