Fog/stratus product: MODIS vs GOES

May 20th, 2008 |

MODIS + GOES fog/stratus product + topography (Animated GIF)

Comparisons of the 1-km resolution MODIS fog/stratus product with the 4-km resolution GOES fog/stratus product help to underscore the improved ability to detect subtle features using higher spatial resolution satellite data. AWIPS images of the MODIS and GOES-11 fog/stratus products (plus topography) covering the Monterey and Fresno, California regions on 19 May 2008 (above) showed a patch of fog over Monterey (KMRY), Watsonville (KWVI), and Salinas (KSNS), with a narrow finger of fog that extended southeastward into the Salinas River Valley.

Farther inland over central California, the MODIS fog/stratus product imagery revealed a noisy “false fog/stratus signal” over parts of the San Joaquin Valley, due to the high emissivity of desert soils that covered the non-agricultural portions of the valley (the contrasting patchwork of green agricultural fields versus brown to gray non-agricultural areas was very evident on 250-m resolution MODIS true color imagery from the previous day) — regions with a lower MODIS Normalized Difference Vegetation Index (NDVI) generally corresponded with regions that exhibited a more pronounced “false fog/stratus signal” (below).

MODIS fog/stratus + NDVI product (Animated GIF)

Images centered off the coast of Southern California and Baja California on 20 May 2008 (below) revealed several ship tracks in the marine stratocumulus cloud deck that was offshore. Once again, such small-scale features showed up with greater clarity on the MODIS fog/stratus product imagery. These comparisons give a bit of a preview of the types of improved products that will be available using the Advanced Baseline Imager (ABI) instrument on the upcoming GOES-R satellite (scheduled to be launched in 2014), which will offer IR imagery and products at a 2-km spatial resolution (at 5-minute intervals on a routine basis).

MODIS + GOES fog/stratus product (Animated GIF)

Another tropical disturbance over Myanmar

May 13th, 2008 |

Meteosat-7 IR images (Animated GIF)

Just 11 days after deadly Cyclone Nargis made its devastating landfall in Myanmar (also known as Burma), Meteosat-7 IR imagery from the CIMSS Tropical Cyclones site (above) showed a new tropical disturbance that was moving northwestward across the Irawaddy Delta region of Myanmar on 13 May 2008. The Joint Typhoon Warning Center issued the following Tropical Cyclone Formation Alert at 20:30 UTC:

WTIO21 PGTW 132030
MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC//
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
RMKS/
1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN 150 NM EITHER SIDE OF A LINE FROM 16.5N 96.1E TO 19.4N 92.1E WITHIN THE NEXT 12 TO 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY ISSUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME. WINDS IN THE AREA ARE ESTIMATED TO BE 25 TO 30 KNOTS. METSAT IMAGERY AT 131800Z INDICATES THAT A CIRCULATION CENTER IS LOCATED NEAR 16.7N 95.7E. THE SYSTEM IS MOVING WEST-NORTHWESTWARD AT 06 KNOTS.
2. REMARKS: RECENT ANIMATED INFRARED SATELLITE IMAGERY AND A 121210Z SSMI MICROWAVE IMAGE INDICATE PRONOUNCED LOW-LEVEL CYCLONIC TURNING OF CONVECTION AT THE WESTERN END OF THE MONSOON TROUGH. HOWEVER, MORE RECENTLY, CONVECTION HAS WANED SOMEWHAT IN RESPONSE TO LAND INTERACTION. THE CIRCULATION CENTER IS CURRENTLY TRANSITING
GENERALLY NORTHWESTWARD ACROSS THE YANGON DELTA REGION OF MYANMAR. OBSERVATIONS FROM YANGON AS OF 131300Z, SUPPORT A 25 TO 30 KNOT CIRCULATION WITH SEA LEVEL PRESSURES NEAR 1000 MB (3 MB PRESSURE FALLS OVER THE PAST 24 HOURS) AND SUSTAINED WINDS AT 10 KNOTS GUSTING TO 20 KNOTS OUT OF THE NORTHEAST. A PARTIAL 130301Z ASCAT
IMAGE ALSO INDICATES STRONG WESTERLIES TO THE SOUTH OF THE CENTER WITH SUSTAINED EASTERLIES TO THE NORTH, FURTHER PROOF OF CYCLONIC TURNING. THE CENTER CURRENTLY LIES UNDER LOW VERTICAL WIND SHEAR JUST SOUTH OF THE SUBTROPICAL RIDGE AXIS WITH FAVORABLE SOUTHWESTERLY DIFFLUENCE ALOFT. THOUGH THE DISTURBANCE IS CURRENTLY OVER LAND, MINIMAL DEGRADATION OF THE LOW LEVEL IS EXPECTED DUE TO THE LOW LYING TOPOGRAPHY AND FAIRLY QUICK TRANSIT
OVER THE LOW-LYING COASTAL REGION OF SOUTHERN MYANMAR. EMERGENCE INTO THE BAY OF BENGAL IS EXPECTED WITHIN THE NEXT 12 TO 18 HOURS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 25 TO 30 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1000 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS GOOD WITH THE ONLY LIMITATION BEING TEMPORARY LAND INTERACTION.

CIMSS satellite-derived atmospheric motion vectors and products (below) indicated that the upper-tropospheric winds, divergence, and deep layer shear were all relatively weak  over the region at that time.

satellite-derived upper tropospheric winds and divergence (Animated GIF)

Satellite signatures of the Mississippi Alluvial Valley

May 12th, 2008 |

MODIS images (Animated GIF)

AWIPS images of the MODIS visible channel along with the Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature (LST) products (above) depicted the areal extent of the Mississippi Alluvial Valley (MAV) on 12 May 2008. This physiographic feature represents the historical flood plain of the lower Mississippi River, which stretches from the confluence of the Ohio River to the Gulf of Mexico. Much of this land has been converted to agricultural use during the past century — because of the marked differences in soil composition and vegetation density between the MAV and the surrounding forest-covered areas, the MAV shows up as a lighter shade of gray on the visible image, with significantly lower NDVI values around 0.2 to 0.3. In addition, significantly warmer LST values were seen in the MAV, which were 20-30 degrees F warmer (darker red colors) compared to the surrounding forested areas (similar warm LST values were also noted over cities and other heavily urbanized locations).

Classic enhanced-V and anvil plume signatures

May 10th, 2008 |

GOES-12 + NOAA-16 IR and visible images (Animated GIF)

The severe thunderstorm that was producing a significant long-track tornado (approximately 75 miles long, and around 1 mile wide at times) across parts of northeastern Oklahoma and southwestern Missouri on 10 May 2008 exhibited a classic “enhanced-v” signature on both GOES-12 and NOAA-16 IR imagery. The coldest cloud top brightness temperature values in the region of the enhanced-v were -79 C on the 1-km resolution NOAA-16 AVHRR data, compared to -67 C on the 4-km resolution GOES-12 IR data. In addition, the visible imagery revealed a well-defined anvil plume spreading northeastward from the overshooting top region. Large hail (up to 2.75 inches in diameter) and wind gusts to 65 mph were reported around or just after the time of these images at Joplin, Missouri (station identifier KJLN). The long-track tornado produced EF-4 damage, and was responsible for at least a dozen fatalities in the Picher, Oklahoma and the Seneca/Racine, Missouri areas (SPC storm reports | Tulsa OK NWS summary | Springfield MO NWS summary).