Great Lakes Water Temperature Product to Eastern Region Forecasters

SPoRT is preparing a high resolution water temperature product for the Great Lakes region as subset of the enhanced MODIS/AMSR-E SST composite (beta version released last month).  The example below shows significant detail in the surface water temperature structure across sections of each lake.  Forecasters use this information in a diagnostic mode and prognostically (in weather forecast models) to improve the prediction of clouds and precipitation in the Great Lakes region.  This will have significant impact in Lake effect snow situations.

High resolution water temperature of the Great Lakes as observed in the enhanced MODIS / AMSR-E SST product for December 3, 2009 at 0700 UTC.

The product will be available for use in the WRF EMS v3 and in AWIPS early next year.

NASA A-Train Observes Hurricane Ida in the Gulf of Mexico

Hurricane Ida (now a tropical storm) was located in the eastern Gulf of Mexico at 0745 UTC on November 11, 2009.  A descending orbit of the NASA A-Train observed the tropical cyclone.  Here, rain rates estimated from the passive microwave data of AMSR-E are shown (inset), with widespread heavy rains located throughout the northern half of the circulation center.  Further north, estimated precipitation rates decreased with distance from the strongest convection.  Passive microwave brightness temperatures and retrieved rain rates provide additional detail over the traditional infrared appearance, where the structure of the cyclone rain bands is masked by dense cirrus overhead.

In addition to the AMSR-E aboard Aqua, the CloudSat radar passed just to the west of the circulation center.  Radar reflectivity indicates a steady decrease in (detectable) cloud top height moving from 25 to 28N latitude, or decrease in cloud top altitude with distance from the circulation center.  Neither the AMSR-E or infrared data are able to depict the 5 km variability in cloud top height.  The radar also provides value by highlighting the presence of individual convective cores, where reflectivity is likely enhanced by the presence of graupel.  Near the 4-5 km level, the thin band of enhanced reflectivity suggests the presence of the melting level.  This feature does not seem to appear underneath the higher cloud tops at 25 N, however, the disappearance is likely a result of attenuation of the radar signal through the deeper convective cores.  The CloudSat signal is best suited for small particles and ice, and attenuates rapidly in heavy liquid precipitation.  Therefore, returns are limited below the melting level, given the high rain rates suggested by AMSR-E data.

The multiple, yet nearly simultaneous perspectives provided by the A-Train allow for a more complete depiction of precipitation structures, especially for storms that are offshore and out of the range of ground based radars.

Composite of satellite imagery related to Hurricane Ida: rain rates provided by AMSR-E passive microwave retrieval (inset), and CloudSat 94 GHz radar reflectivity cross section (below), with geostationary infrared imagery provided as a background. Infrared image and CloudSat cross section provided by the Naval Research Laboratory.

The NASA A-Train Takes a Second Look at Hurricane Bill

Due to a convenient alignment between the A-Train orbital trajectory and the path of Hurricane Bill along the eastern coastline of North America, the CloudSat radar and AMSR-E radiometer was able to take a second look at the structure of the cyclone and passed very near to, or perhaps directly across, the cyclone center.  This overpass occurred around 18 UTC on August 22, 2009 when Hurricane Bill was classified as a Category 1 storm, with tropical storm warnings issued for Nova Scotia and Bermuda by their respective meteorological agencies.

Passive microwave brightness temperatures depict the convective towers associated with the eye wall, as well as the cyclonic shape of the symmetric rain bands located to the north and south of the storm.  The most intense activity appears to be in the southeast quadrant, while northwest of the storm, activity may have been deterred as the cyclone was impacted by wind shear associated with an upper level shortwave departing the northeastern United States.

The AMSR-E 89 GHz passive microwave radiometer depicts the brightness temperatures associated with Hurricane Bill at 18 UTC, 22 August 2009 as it departs the eastern coast of the United States.

The CloudSat radar follows a similar track to the Aqua satellite, the platform supporting the AMSR-E instrument.  Therefore, once again their observations are nearly coincident in time.  It is unclear whether CloudSat directly sampled across the eye, however, with the center located near the 36th parallel, it is likely that CloudSat is depicting the structure of convection to the north and south of the storm.  The relative lack of convection near 36 degrees may be associated with the eye of the storm, with some shallow convection present.  The outermost rain bands, approaching the coastlines of New Jersey, New York and Massachussetts, are present in the cross section near the 40th parallel.   Numerous, isolated convective towers are evident in the CloudSat cross section, which is again attenuated severely just below the melting level due to the large amount of liquid precipitation.

Assuming that CloudSat sampled the eye, it is interesting to note that it depicts a layer of relatively thick, high altitude cloud which may have obscured the location of the center in visible or infrared satellite imagery.  CloudSat indicates that some shallower convection may be occurring near the eye center, while AMSR-E is able to use passive microwave brightness temperatures to see through these nonprecipitating ice clouds for a clearer shot at the cyclone center.

CloudSat observes the precipitation and cloud structures of Hurricane Bill, then a category 1 storm, as it travels along the eastern coast of the United States.

Finally, the CALIPSO instrument provides imagery of high altitude ice clouds associated with the tropical cyclone.  The highest cloud tops are located near the cyclone center at 36 degrees, and maintain a cloud top altitude of 15 km as in the previous sampling.  Meanwhile, the outer band approaching the United States appears weaker with tops ranging from 8 to 12 km.

The CALIPSO satellite indicates significant lidar backscatter obtained from the high altitude ice clouds associated with Hurricane Bill as it passes along the east coast of the United States.

Passive Microwave (AMSR-E) Observations of Hurricane Bill

In a previous post featuring CloudSat observations of Hurricane Bill, the southern side of the storm appears to have colder cloud tops and a more uniform appearance than the northern half of the cyclone.  However, CloudSat radar reflectivity suggested that clouds observed on the southern side of the storm were thick, midlevel ice clouds with scattered, low topped convection underneath.  This demonstrates the value of the two-dimensional (X,Z) radar profiles in characterizing precipitation structures “underneath” more traditional satellite observations.  The northern side of the storm is less uniform in infrared appearance, but CloudSat detected active, deep convection along the majority of the flight track.

The infrared image can be supplemented by 89 GHz, passive microwave brightness temperatures from the AMSR-E instrument aboard Aqua.  These brightness temperatures are obtained simultaneously with infrared brightness temperatures from MODIS.  The passive microwave brightness temperatures are sensitive to the precipitation mass (ice) within the vertical column, and clearly depict the structure of the hurricane eye wall and outer rain bands.

Passive microwave brightness temperatures (89 GHz) from the AMSR-E instrument aboard Aqua, observing Hurricane Bill on August 19, 2009. The flight track of CloudSat and 94 GHz Cloud Profiling Radar reflectivity are provided in a cross section below.

The SPoRT program provides AMSR-E brightness temperatures to partners in the National Weather Service for a variety of applications, including offshore rain rates, convective percentages, and soil moisture.  Images courtesy of the Naval Research Laboratory and the CloudSat Data Processing Center.

AMSR-E Convective Percent

The AMSR-E Convective Percent (CP) product is shown. The CP ranges from 0 (completely non-convective) to 100 (completely convective).  This product is mainly used in research but can occasionally be useful for operational use when other resources may be lacking.  Basically it is a measure of the amount of ice in the atmospheric columns at each pixel.  This can be used as a surrogate for convective intensity.  There are some limitations, one of which is the zero flagged areas in the most intense convection (in NE Arkansas).  See the SPoRT AMSR-E product summaries for more information.

AMSR-E Convective Percent - 05 August 2009 - 07:33 UTC

AMSR-E Convective Percent - 05 August 2009 - 07:33 UTC

AMSR-E Rain Rate for Coastal WFOs

Many NASA/SPoRT partners have coastal forecast issues and are impacted by precipitation  from offshore storms and tropical cyclones.  Outside of the radar coverage it can be difficult to know how much precipitation is occurring with impending tropical convection or cyclones.  The AMSR-E instrument provides a rain rate product to aid these situations.  The products from AMSR-E were highlighted via the NWS Coordination call with SPoRT that occurred in early August 2009 and a bundle of files and instructions to ingest and display this data via SPoRT into AWIPS was made available via ftp site. Below is an example of the AMSR-E rain rate as it fills in where radar coverage ends, and it provides instantaneous rain rates vs hourly totals.  Notice the greater rain rate values in the northwest area of the tropical cyclone as well as the large rates just outside the radar coverage.  While AMSR-E data will not be as timely as radar estimates, suffering a 3-4 hr latency, it fills a gap for coastal and tropical areas and provides more accurate picture for hydrologic impacts and impending tropical cyclone events.

AMSR-E instantaneous rain rate showing more accurate depiction of precipitation over the 1-hour stage 4 estimates below.

Stage 4 radar 1-hourly rainfall.