Tropical Disturbances in both Hemispheres

February 19th, 2019 |

Morphed Total Precipitable Water for the 24 hours ending 0100 UTC on 19 February 2019 (Click to enlarge)

Morphed Total Precipitable Water imagery (from this site) for the 24 hours ending at 0100 UTC on 19 February 2019, above, shows two Tropical disturbances spinning on either side of the Equator. Cyclone Oma in the Southern Hemisphere was northwest of New Caledonia in the Coral Sea. A second disturbance over the north Pacific, albeit very close to the Equator, was near Pohnpei and will pass near Chuuk later this week. Interests in Micronesia should pay attention to this area of disturbed weather.

Himawari-8 Clean Window imagery (10.41 µm) (courtesy JMA), below, shows the better organization of Oma in contrast to the more disorganized nature of the tropical wave over Pohnpei.

Himawari-8 AHI Clean Window (10.41 µm) Infrared Imagery, 1400 UTC 18 February – 0230 UTC 19 February 2019 (Click to play animated gif)

Refer to the CIMSS Tropical Webpage (Link) for more information on Oma. The National Weather Service on Guam is issuing statements on the tropical system in Micronesia. (From 0245 UTC on 19 February 2019, for example) (Update: This is now Tropical Depression 02W; a projected path as of 1200 UTC on 19 February is here. The current forecast has this storm achieving typhoon status late Wednesday).

GOES-17 Data Fusion: An example, and where to find the data

February 15th, 2019 |

GOES-17 Water Vapor Imagery. 6.19 µm (top row), 6.95 µm (middle row), 7.34 µm (bottom row); Left Columm:  Imagery from the ABI; Right Column:  Data Fusion Imagery created using the GOES-17 ABI Band 13 (10.3 µm) Imagery. Animation from 0902 UTC – 1727 UTC. Data Fusion imagery is not computed for the first or last images. Click to play mp4 animation.

The GOES-17 Loop Heat Pipe issue means that certain infrared bands lose data integrity at certain times, times that vary over the course of the year. Late February is a time of year when the impacts on data are very noticeable (This figure — from this blog post — shows other times of the year when the issue is most noticeable).  The Data Fusion process that uses GOES-17 ABI Band 13 imagery (relatively unaffected by the LHP issues) can create approximations of the missing imagery.  This allows for qualitative views of those missing bands.

The animation above (click here for an animated gif) shows GOES-17 Water Vapor Channels on the left (6.19 µm, 6.95 µm and 7.34 µm) and GOES-17 Data Fusion images on the right. At the beginning of the animation (0902 UTC), Data Fusion is not implemented; it uses information at 0902 to create subsequent imagery, however. In the first few frames of the animation, the impact of the LHP warming are not apparent. By 1007 UTC, however, the GOES-17 Water Vapor Bands are becoming noticeably warmer than the Data Fusion imagery. (An initial signal that LHP issues are starting is a general warming in the imagery). Data dropouts start at 1102 UTC, first at 7.34 µm, then at 6.95 µm and finally at 6.19 µm. By 1202 UTC, data integrity is lost completely, but Data Fusion maintains a signal that allows a user to qualitatively track features in the image. Shortly after 1500 UTC, data starts to reappear, initially mostly at 6.19 µm, then 6.95 µm and finally at 7.34 µm. By 1632 UTC, the PACUS (Pacific/CONUS) image shows data, but it is cooler than the Fused data (Note the cooler cloud top temperatures in all three water vapor bands).

Warmth going into LHP Data Drop-outs and coolness coming out of LHP Data Drop-outs have been documented in this directory tree that compares GOES17 and GOES16 imagery in a region in between the two satellites (a region with similar view angles). The figure below (from here, accessible from this website) shows that GOES-17 brightness temperatures (in red) are warmer than GOES-16 (in blue) before data loss, and cooler than GOES-16 immediately subsequent to data loss.

GOES-17 (red) and GOES-16 (blue) brightness temperatures for an small domain midway between the two sub-satellite points. The GOES-17 6.19 Image at 1552 UTC is also shown (Click to enlarge).

Fusion Data (in the form of netCDF files written comforming to mission standards; the netCDF files are readable by SIFT and McIDAS-V, for example) are available via ADDE from the SSEC Data Center. Send an email here for more information. Imagery is also available at the SSEC Data Center via the geo browser.

Moisture Streaming towards Southern California

February 14th, 2019 |

Morphed Microwave Total Precipitable Water, 1800 UTC 13 February to 1700 UTC 14 February 2019 (Click to enlarge)

A potent Atmospheric River is affecting the California Coast on 14 February 2019. The morphed microwave imagery, above (from this site), shows rich moisture from deep in the tropics moving onto the southern California and northwest Mexican coasts.  The animation below shows the Layered Precipitable water — also a product derived from microwave imagery — for the same time period, but at 3-hour time steps (from this site).  An interesting feature is that the 850-700 hPa moisture layer is not as continuous back to the tropics as the other 3 layers.

Advected Layer Precipitable Water, 18z 13 February to 18z 14 February 2019 (Click to enlarge)

You can also infer a large influx of moisture from the low-level water vapor imagery, as shown in the short animation below from GOES-17, from 1617 UTC (just as Loop Heat Pipe issues that cause missing data were ramping down) to 1857 UTC. One might also infer a long-duration event from this animation!

GOES-17 ABI Band 10 Infrared 7.3 µm Imagery (Low-Level Water Vapor Band) from 1617 UTC to 1857 UTC on 14 February 2019 (Click to animate)

The GOES-R All-Sky Total Precipitable Water product (from this site) is as yet produced only from GOES-16 data (The Loop Heat Pipe problems have a strong impact on all Baseline products, including Legacy Profiles that are used to create Total Precipitable Water, which impact is still under investigation). The western Pacific is on the limb of this product, but it does capture the deep moisture moving towards southern California.

GOES-16 All-Sky Total Precipitable Water, 1400 UTC on 14 February 2019 (Click to enlarge)

Much of the San Diego National Weather Service Forecast Office County Warning Area is under Flood and/or Wind Warnings! See the Screen Capture below from 1121 AM Pacific Standard Time.

Warnings (as of 11:21 AM PDT on 14 February 2019) over the San Diego County Warning Area (Click to enlarge)

Data Fusion to mitigate Loop Heat Pipe data dropouts with GOES-17

February 13th, 2019 |

GOES-17 Band 10 (7.34 µm) imagery, 0900-1700 UTC on 13 February 2018 (Click to animate)

(The Experimental GOES-17 Data Fusion link is here).

GOES-17 is now operational as GOES-West at 137.2º W Longitude, as noted here and elsewhere. However, Loop Heat Pipe (LHP) problems persist (as noted here and here and here), with the effect varying seasonally. Because of the Loop Heat Pipe malfunction, the Advanced Baseline Imager warms up, emitting radiation at wavelengths similar to those being sensed from the Earth. This does not happen during the day when the ABI instrument is pointing towards the Earth and the Sun is behind the satellite. During the night, however, the sun illuminates the ABI instrument and warms it. This effect is most noticeable (and detrimental to the imagery) around the solstices. The animation above shows the effects of the Loop Heat Pipe on Band 10, the low-level water vapor imagery. Starting at about 1015 UTC, there is a perceptible warming of the image, globally, shortly after that the image integrity is lost and the data become unuseable. At 1615-1630 UTC, the instrumentation cools enough to produce, again, useable imagery.

The chart below shows how the temperature of the focal plane in the ABI changes throughout the course of the year. The differences between Northern Hemisphere Vernal and Autumnal Equinoxes occur because the Earth is closer to the Sun at the Northern Hemisphere Vernal Equinox. The chart also shows the effects of ‘Eclipse’ — when the satellite moves through the Earth’s shadow. When the ABI is in the Earth’s shadow, it is not being heated by the Sun (and that’s why the GOES-R Series carries batteries to power the satellite at that time). The reduced heating occurs between 26 February and 14 April in the Spring, and between 30 August and 16 October in the Fall. The chart also contains for the longwave infrared bands the temperature at which the heat from the satellite increases the likelihood of bad data.

Warmest Focal Plane Temperature as a function of Year. Also included: the threshold temperatures when the ABI Detection is affected by the warmer Focal Plane. The step in values near both Equinoxes occurs when a Yaw Flip is performed on the satellite (Click to enlarge)

Note in the plot above that Band 13 and Band 14, the clean window and longwave infrared window bands at 10.3 µm and 11.2 µm, respectively, is relatively unaffected by warming. This 10.3 µm animation (spanning the same times as the animation above) shows subtle features that are related to warming because of the faulty Loop Heat Pipe, but overall, data integrity is preserved.

The GOES-17-only fusion solution for mitigating data outages uses GOES-17 ABI Clean Window (10.3 µm) radiances to create missing spectral band radiances. In this method, the last full set of calibrated radiances at time t0 is marked (For GOES-17 at present this is done at 0900 UTC). Then, for subsequent times when LHP issues cause missing data, a so-called k-d tree search (discussed in this paper: Weisz, E., B. A. Baum, and W. P. Menzel, 2017: Construction of high spatial resolution narrowband infrared radiances from satellite-based imager and sounder data fusion. J. Appl. Remote Sens. 11 (3), 036022, doi: 10.1117/1.JRS.11.036022) is performed on time t0 infrared window band 13 measurements to find the five t0 pixels that best match each time t infrared window band 13 pixel; the five k-d tree time t0 matches for each pixel are then averaged for all ABI IR spectral bands to estimate ABI bands at time t for that pixel.

In other words, the fusion method (1) finds the five best matches of time t0 Band 13 measurements for each time t Band 13 measurement and then (2) uses the average of those t0 matches for each missing spectral band to create a fusion estimate at time t. Using time 0900 UTC for t0, when Loop Heat Pipe issues subsequently impact data quality, the Band 13 image at that time is used to predict what the other bands would look like — based on the relationship established for Band 13 measurements between time t and time t0 at 0900 UTC. The fusion method is most challenging for the Band 10 imagery — because it is the least correlated with Band 13 (especially in regions of clear skies). In contrast, a window channel like Band 11 is highly correlated with Band 13 and the Data Fusion product has few artifacts. This animation compares Band 13 and Band 11 — very similar! — and Band 13 and Band 10 — not that similar, except in regions of clouds.

A resultant image is shown below. The left-most image is the unusable GOES-17 Band 10 image. The middle image shows the GOES-17 water vapor image produced via data fusion; the right-most image is the corresponding GOES-16 Band 10 image over the same region (a region that is midway between the two satellite nadirs so that view angle differences are minimized). There are some subtle differences; in particular the Fusion product shows values that are cooler than GOES-16 in some regions, but the qualitative aspects of the match are good.

(The GOES-17 Imagery below pre-dates the 1800 UTC 12 February 2019 time when GOES-17 became operational and should therefore be considered preliminary and non-operational)

GOES-17, GOES-17 Data Fusion, and GOES-16 Low-Level Water Vapor (Band 10, 7.3 µm) Imagery, 1300 – 1445 UTC on 4 February 2019 (Click to play mp4 animation)

Data Fusion Imagery is available at the SSEC Geo Browser (Link).  It is a separate drop-down menu (‘GOES-17 Fusion’) and should be considered experimental.  The animation below shows the transition between non-fusion and fusion data.  Here is a full-disk animation from 13 February (1200 UTC to 1700 UTC) that shows Fusion Data transitioning back to GOES-17 data as the Loop Heat Pipe issues end in the morning.

GOES-17 Low-Level water vapor imagery (7.3 µm) at 1100, 1115 and 1130 UTC. Data Fusion was used to produce the 1130 UTC image (Click to enlarge)