Alaskan Sunshine Doesn’t Burn the 24-hour Microphysics Product

In collaboration with the Geographic Information Network of Alaska (GINA) at the University of Alaska, NASA/SPoRT generates two VIIRS and MODIS microphysics satellite products for use by the National Weather Service in Alaska in assessing the presence of low stratus clouds: the RGB Night-Time Microphysics product, or simply NT Micro, and the 24-hour Microphysics product, or 24hr Micro. Being RGBs, these two products result from combining a number of satellite channels. Both RGBs use the 12.0-10.8 micron difference as the red channel, and both use the 10.8 micron signal as the blue channel. But the NT and 24hr Micro products diverge in what they use for the green channel: the NT Micro uses the classic 10.8-3.9 micron difference (the legacy “fog product” that has been employed by meteorologists for years), while the 24hr Micro uses a 10.8-8.7 micron difference. The motivation behind this divergence in approach is that the 8.7 micron channel is not affected by solar reflectance, while the 3.9 micron channel definitely is affected by solar reflectance. As a consequence, the NT Micro changes its appearance as night gives way to day and is not usable once the sun comes up, while the 24hr Micro provides a consistent depiction of the clouds both day and night.

Patchy low stratus clouds covered parts of southwestern Alaska on December 17, 2014. What follows are two animations taken from AWIPS at the NWS office in Fairbanks, Alaska that toggle images from around 15Z and 21Z, with the image near 15Z occurring during darkness and the image near 21Z occurring during the light of day. While there isn’t much sunshine in southwestern Alaska in December, there is still enough to cause trouble for the NT Micro with its reliance on the 3.9 micron wavelength in the green channel.

toggle NT Micro

The top animation is a toggle of the NT Micro. Note how at 15Z, in darkness, the green-yellow colors indicate the low stratus in southwest Alaska. But at 21Z, in daylight, these same clouds appear pink despite the continued presence of the low clouds. Observations from the village of Sleetmute (METAR identifier PASL), Alaska are a case in point. The ceiling and visibility plots at a number of METAR sites are overlaid in light blue text, with Sleetmute plotted just northwest of the yellow zone number “152” at the center of the image. At 15Z Sleetmute has good visibility but a ceiling down at 500ft overcast. At 21Z Sleetmute still has good visibility, and the ceiling remains low, in this case at 400ft broken 1100ft overcast. That’s not much of a change in the METAR over this span of time despite the huge change in the appearance of the NT Micro product between 15Z and 21Z.

The bottom animation toggles the 24hr Micro over the same span of time, from 15Z to 21Z, and there isn’t much change in the appearance of the 24hr product from darkness to daylight. The deck of low clouds over southwest Alaska appears bright yellow in this product, day or night.

toggle 24hr Micro

Every product has its strengths and weaknesses. At night the NT Micro shows more details and is perhaps preferable to the coarser looking 24hr Micro. But during the transition from darkness to daylight the NT Micro is not usable, while the 24hr Micro provides consistent imagery. The 24hr Micro product may prove increasingly useful in Alaska as the months progress and the long dark Alaskan winter gives way to a summer of almost continual daylight.

QPE (NESDIS) product assessment in Alaska

As part of its GOES-R Proving Ground activities, SPoRT is partnering with Bob Kuligowski (NESDIS) and Alaska WFOs and RFC to assess the Quantitative Precipitation Estimate (QPE) product suite at high latitudes.  The intensive evaluation period will begin July 15 and go until September 15.  The QPE product has been developed in preparation for GOES-R. The QPE algorithm uses the current GOES longwave IR and water vapor channels and is calibrated in near-realtime using microwave sounding retrievals from a variety of satellites (TRMM, NOAA 18 & 19, METOP-A and B). In the GOES-R era, an additional 3 IR channels will be incorporated with the improved resolution to 2km. While the QPE product is better suited to convective type precipitation, this assessment with Alaska operational users is looking at the value of the product at high latitude and what adjustments might be made to improve its use in regimes with more stratiform, low-top precipitation.  Below is a comparison of the QPE to the AK RFC post analysis of the 24-hour precipitation ending on July 7 at 1200Z.  While fairly good agreement exists in some areas, the question is how well the QPE product can provide guidance in low density observation areas at high latitude.

To see a web display of product suite over several domains go to the SPoRT Real-Time Data page for QPE.

20130710_1200_sport_nesdis_alaska_qpe_024

QPE 24-hour accumulation ending July 10, 2013 at 1200Z over Alaska domain. Product created by NOAA/NESDIS, transitioned via NASA/SPoRT for use in AWIPS by NWS users.

has_p24nmap-2_QPEcomparison20130710_1200

Web graphic of 24-hour precipitation estimate from the Alaska River Forecast Center ending July 10, 2013 at 1200Z.

Windsat validation / intercomparison example in Alaska

Comparison of Windsat ocean surface vectors with GFS, NAM, and in situ observations for Chukchi Sea, AK on October 27, 2011.

John Lingass (WCM in Fairbanks asked us to post this for him) The GFS and NAM output for this time frame of WindSat observation look very close to the WindSat observations, especially for the higher wind speeds. Although ship observations were not available, which would be the ultimate data for validation, the surface observations at Gambell (PAGM) and Savoonga (PASA) on St. Lawrence Island have some utility for comparison as the wind flow is coming from an unobstructed direction with regard to the wind instruments at these locations. The WindSat Data shows very good agreement with these land observations in this case. As for synoptic features, a 991 mb low was stationary and slowly weakening near the Bering Strait, the wind circulation excellently indicated by the WindSat data.