Low clouds and fog in the N. Gulf and Texas regions caused MVFR/IFR/LIFR conditions over a large area. The VIIRS Nighttime Microphysics RGB shows aqua to gray coloring to represent these features. In the RGB the scene is fairly complex with high and middle clouds (reds, blues, purples, tans …..). The RGB composite uses the traditional 11-3.9um difference (seen below) and combines other channels to better illustrate the low cloud features between the middle/high clouds. The RGB also improves the characterization of the thick, cold cloud tops associated with the cutoff low producing precipitation along the coast and southern states when compared to the simple 11-3.9um. Other “microphysical” RGBs are possible during the day or in a form that can be applied both day and night (i.e. 24hr product).
Archive for the ‘JPSS Proving Ground’ Category
Yet another bout of snow, sleet and ice recently affected much of the Tennessee and Ohio Valley regions. Although clouds were clearing in western portions of this region, allowing for a broad scale satellite view of the newly laid snow/ice field, eastern portions remained cloud-covered until sunset. While ground reports contain valuable information about the depth of snow and/or ice, they’re only point measurements, so assumptions often have to be made about the spatial extent of the snow, until satellite observations are available (unless clouds obscure). So, those observations would have to wait until the next day, during visible sunlight hours…or would they? Well, not exactly…which is the point of this blog post.
The image below (Image 1) is a Snow/Cloud RGB produced by SPoRT and disseminated to collaborative NWS field offices. The green colors represent the background surface (grass, trees, cities, etc.), while the deeper reds represent snow/ice cover. White colors depict clouds, while reddish-white represents very cold clouds containing ice crystal clouds. Notice the swath of snow that is visible from NE Texas into the Midwest. Meanwhile, clouds obscure any snow/ice in eastern areas.
Clouds had pushed eastward by sunset, but did still not move far enough to provide a clear indication of the eastward extent of the snow/ice field that had just fallen. However, once the VIIRS Day-Night Band imagery became available later that night, the spatial extent of the snow and ice could be fairly easily observed. Notice in the next image (Image 2) the snow and ice cover that was apparent over portions of the Tennessee and Ohio Valley region.
This type of imagery can be helpful for operational forecasters when trying to assess the potential societal impacts of lingering snow and ice, and also the impacts on sensible parameters such as temperatures and relative humidity, which can help improve weather forecasts.
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.
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.
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.
I’ve written about the operational utility of Day-Night Band (DNB) RGB imagery several times in the SPoRT blog, and here I’m going to take the chance to do that again. First, just some brief background information in case you’re not familiar with this type of imagery. The DNB RGB is composed of a long wave IR channel (~10.8 µm), which is assigned to the blue color component of the RGB recipe, while the DNB channel (0.7 µm) is assigned equally to the red/green colors of the RGB. SPoRT produces two DNB RGB products: Radiance and Reflectance. I typically prefer the Radiance RGB for operational uses since it is composed of the raw data (emitted and reflected light) from the sensor. Sure, cities are quite bright in the imagery, but the cloud features also stand out better compared to the reflectance product, where the data are normalized by the available amount of moonlight. Below are a few observations from the Suomi-NPP VIIRS instrument during this most recent full moon cycle.
First, take a look at the images below from the SE half of the CONUS on the early morning of December 7th. The top image (Image 1) is a Nighttime Microphysics RGB at approx. 0736 UTC, while Image 2 is a DNB Radiance RGB valid at the same time. While this type of imagery is far superior to legacy IR imagery (even enhanced with fanciful color curves), there are proper operational forecasting/analysis applications that one has to consider. The Nighttime Microphysics RGB is generally more useful for distinguishing different cloud types (e.g., low stratus vs fog, thin cirrus vs thick cirrus, etc). After at least a year of viewing the DNB imagery, I think perhaps the best application of these types of imagery (at least with respect to operational forecasting) lies in the ability to view low clouds through cirrus at night. No other imagery available to forecasters offers this capability currently. Take for example these first two images below and pay close attention to the cloudy regions stretching from the central Plains into the lower Mississippi Valley.
Notice that in the Nighttime Microphysics RGB the expansive deck of low stratus across much of Kansas, southwestern Missouri and Oklahoma is almost entirely obscured by the cold cirrus clouds. Of course, this is only realized upon looking at the DNB imagery. Details in the low stratus can also be observed in the DNB imagery, such as the cloud banding stretching SW-NE across much of northern Louisiana and Mississippi. Since the cloud bases in this imagery were mostly at MVFR and IFR levels with respect to aviation forecast concerns, knowledge about the details and characteristics of the low clouds are very important.
The next series of images from the New England region in the early morning hours of December 9th again demonstrates this application of the DNB imagery.
In the images above, notice that the extensive low cloud deck across the region that spans from Maine to at least as far south as northeastern North Carolina cannot readily be observed either in the legacy IR (10.8 µm ) imagery or in the Nighttime Microphysics RGB. However, more details about the low clouds can be discerned from the DNB imagery. Sure, cirrus clouds are optically thick enough to prevent viewing of any low clouds in the NY metro area. Nevertheless, the advantages of the DNB imagery for detecting low clouds beneath thin cirrus can clearly be seen. Again, as expressed earlier, this type of imagery certainly offers application for aviation forecasting, in particular.
Lastly, here are some observations from just this morning (Dec 10th) over the Rio Grande Valley region.
In the VIIRS IR image (Image 6) just as in previous IR imagery the cirrus clouds obscure the presence of any clouds beneath. However, the patchy low clouds in eastern New Mexico can be much more easily seen in the DNB imagery. In the area between Midland, TX (KMAF) and Fort Stockton (KFST), a forecaster might have made the assumption that the low clouds were continuous based on the observations alone and without the aid of the DNB imagery. Yet, what becomes noticeable in the DNB imagery is that a gap exists in the low cloud deck.
Of course, with all of this said, the availability of the imagery severely limits its application for operational forecasting and analysis. Generally, only one or two passes are available over a given location on any night. Also, due to moonlight limitations, the imagery are only available for about half of the month…at best. I can only lament that the DNB imagery will not be available on a geo-stationary platform (at least anytime soon). Nevertheless, understanding the limitations of the imagery while also appreciating its advantages can offer operational utility when applied properly to a forecast challenge.
SPoRT has been investigating options to obtain near-real time NUCAPS (NOAA Unique CrIS and ATMS Processing System) data to expand the ozone products to Suomi NPP retrievals. The AIRS ozone products cover a Northwestern Hemisphere domain (Link to SPoRT AIRS products) and were specifically created for the National Centers (WPC and OPC) to aid interpretation of the Air Mass RGB for identifying and forecasting stratospheric intrusions that can lead to rapid cyclogenesis and hurricane-force wind events in the North Atlantic and North Pacific Oceans. The AIRS data are obtained from NASA Land Atmosphere Near-Real Time Capability for EOS (LANCE), rather than Direct Broadcast, so that the products can be created in hourly swaths that cover the OPC domain. Since the ozone products are created from polar-orbiting retrievals, forecasters are eager for better temporal and spatial resolution. Use of retrievals from newer instruments such as Suomi-NPP CrIS/ATMS can provide additional overpasses to improve spatial and temporal resolution when paired with AIRS.
Suomi NPP data are available on the NOAA Comprehensive Large Array-Data Stewardship System (CLASS). Typically data are obtained from CLASS by choosing options such as data type, domain, and time on the website and placing an order. Depending on the size of the order, it can take about an hour to 24 hours for your request to be processed and ready for download via ftp. Manually placing an order is not an optimal approach for near-real time data processing and product development.
Recently SPoRT investigated the CLASS subscription service and has had success in obtaining NUCAPS data with a 2-3 hour latency. The CLASS subscription service is a valuable tool, comparable to NASA LANCE, for obtaining near-real time NUCAPS data. Others in the community who are interested in obtaining NUCAPS data with reduced latency and need a larger domain than what is available from Direct Broadcast should investigate the CLASS subscription service. Below is a outline of steps to set up a CLASS subscription for NUCAPS data.
First go to CLASS, create a user account and sign in. Click on “Subscriptions” in the left side menu. Choose your data product from the dropdown menu and click “Add New” to begin setting up the subscription details. For NUCAPS choose S-NPP Data Exploitation Granule Data (NDE_L2)
Next, set up the search criteria for your subscription by choosing the domain either by making a box on the map or entering latitude and longitude values beside the map. Click on the box next to “NUCAPS Environmental Data Records” and click on “S-NPP”. Click on “Delivery Options” to continue.
Last set up the delivery options. Choose “yes” for a recurring schedule and set the start and end dates. The start and end dates do not include the year, therefore you’ll need to modify the start and end date as the end of the year approaches. Choose whether or not you want email notifications. I would initially choose “yes” so you can start to gauge how quickly your subscription is being processed from the time your data arrives in CLASS. Note that you will get an email for every granule and sometimes the email notifications are delayed quite a bit after your data is ready. The notifications are initially helpful as you first set-up your subscription. As a side note I did enjoy spamming myself with approximately 20-30 CLASS email notifications per hour when I first set up my subscription so I could see how it was working and could gauge the data latency. Most important, choose how often you want to receive data in the dropdown list beside “Include delivery manifest”. I’ve chosen “Every 1 hour”, but depending on the product and your needs, you can choose any interval from 1-24 hours. Features such as the digital signature and checksum aren’t always necessary but you can decide if you need them by reading about them on the class help pages. Now click “Save” to finish.
Once your subscription is set up, you can log in at any time to view, modify, or disable your subscription. Just click on “Subscriptions” on the left side menu after you have logged in.
Once your data arrives in CLASS your order will be processed. Therefore the subscription service can provide automatic distribution of near-real time products as long as the data is arriving in CLASS near-real time. If the data is not pushed to CLASS near-real time by the product developer or NDE than the subscription service can’t be used for near-real time purposes (unless you don’t mind a 6-24 hour or longer latency). Not all Suomi NPP products are pushed to CLASS in a real-real time capability. Thankfully NUCAPS is pushed to CLASS relatively quickly after it is processed and can be obtained via CLASS near-real time. Your subscription will have a unique ID and your order will be available on the ftp site in a directory named with your username and subscription ID. The data will also be available via a unique http site named with your username and subscription ID. Now your data is in one place and can be accessed via scripting and ftp without manually submitting an order on CLASS.
Latency of products getting to CLASS and figuring out how to order data without manually submitting an order on the website have been the largest deterrents for SPoRT using CLASS data for real-time product development. Not all Suomi NPP data is immediately pushed to CLASS near-real time, however contacts at NESDIS have indicated that in the next 6-months or so, more Suomi NPP data will be pushed to CLASS in near-real time mode. Utilizing the CLASS subscription service opens up a new opportunity for SPoRT and the community to use NUCAPS data (and in the near future, other Suomi NPP data sets) from CLASS for product development.
More information on CLASS subscriptions can be found within the CLASS help pages.
Starting around 07Z last night, we noticed a station in the far northeast corner of Colorado reporting some reduction in visibility, with no other stations nearby reporting any reduction. We couldn’t see any indication in the 11u-3.9u IR satellite imagery. Once the VIIRS DNB imagery came in of the 09:04UTC imagery set, it was definitely evident in the Nighttime Microphysics channel, slightly in the Dust RGB channel, but not at all in the other DNB channels. Good to know the sensor was reporting correctly!
Seen above, top to bottom: VIIRS DNB Reflectance RGB, IR Longwave, Dust RGB, Nighttime Microphysics imagery. The latter definitely shows the small patch of fog clearly with the whiter (lower) clouds.
I wanted to follow up with this sooner, but I’ve been rather busy preparing for the NWA conference. Yep, I tend to be one of those “last-minute” people. Anyway, just last week I posted an example showcasing the advantage of the VIIRS Day-Night Band Radiance RGB in detecting fog through cirrus clouds. The next day, SPoRT collaborator Doug Schneider (Morristown WFO), followed up with another great example that I wanted to share. I’m just going to take an excerpt from an email he sent to the Morristown staff…
“I know I’ve been sending out quite a few emails lately about NASA SPoRT products, so please bear with me, but I thought this was a great example of how they can add value.
I’ve mentioned the MODIS/VIIRS Fog product before, but sometimes there are better products available for identifying fog, especially when thin cirrus are present. In the MODISVIIRS Fog product image that is attached, you can see that it is difficult to see the extent of fog. There’s clearly some in the Sequatchie Valley, but there is also some in the NE TN/SW VA area that can’t be easily seen.
The attached MODIS/VIIRS Nighttime Microphysics product also shows fog in the southern areas where it is clear (fog is light blue colors), but cirrus obscures NE sections.
The VIIRS Day/Night Band Radiance RGB product does the best job showing the extent of fog. Fog is clearly identified in the valleys of SW VA and NE TN, despite the presence of cirrus. The extent of fog is also more easily seen in the central and southern valley areas.
The attached menu image shows where you can find the Day/Night Band Radiance RGB product under the Satellite -> NASA SPoRT -> Polar Imager -> MODIS/VIIRS -> SR East menus.
Remember that these products are from a polar-orbiting satellite, and may only be available once a night, usually between 07z and 10z.”
I’ve included the images he referenced below, and circled the specific area of fog in NE Tennessee / SW Virginia that he was mentioning.
This is exactly the kind of inter-office sharing SPoRT is looking for from our close partners. We greatly thank Doug and the Morristown office for their collaborative efforts!