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1、Hurricane Ivan: 15 Sept 04 approaching the Gulf Coast,SeaWiFS view of Hurricane Ivan was collected at 1:50 PM Central Daylight Time as it approached the U.S. Gulf Coast. The forth tropical storm to hit Florida in only 6 weeks. Credit line for all images: Provided by the SeaWiFS Project, NASA Goddard
2、 Space Flight Center, and ORBIMAGE,Gene Feldman, NASA GSFC, Laboratory for Hydrospheric Processes, SeaWiFS Project Office (gene.c.feldmannasa.gov),The Ice, Cloud, and land Elevation Satellite (ICESat) has used its sensor, the Geoscience Laser Altimeter System (GLAS) to acquire precise altimetry data
3、 along a specific pattern of ground tracks during three separate operations periods in 2003 and 2004. On 10/3/04, a fourth operational period was begun in this same pattern. ICESats first operational period gathered data in a more broadly-spaced track pattern. “Repeat track“ data allow researchers t
4、o evaluate the consistency of ICESats measurements, the factors that influence that consistency, and detect changes that may have occurred between observations.,As illustrated in the following slides, ICESat can measure specific ice sheet features with exceptional resolution and precision. ICESats T
5、rack 1322 crosses the ocean surrounding Antarctica, to the Getz Ice Shelf, up the steep slopes of the Flood Range to the ice-covered summit of volcanic Mount Moulton, then across the West Antarctic ice sheet divide, and into the Ross Ice Shelf drainage basin. Despite variable atmospheric conditions
6、during the three repeat-track acquisition times (note color breaks in the topographic profile due to thick clouds), the ability of ICESat to measure elevations across an ice sheet is clear. The second slide illustrates the ICESat data over just the summit portion of Mount Moulton as well as a proxy
7、for the cloud cover at the time of acquisition (gain number). The data from the Laser 2a period was acquired through relatively clear skies as indicated by the lowest gain numbers. The data from the Laser 2c period was acquired when significant clouds wreathed the summit, especially on the north (le
8、ft) side. The Laser 2b acquisition appears to have been through some clouds across the summit that increased to the south (right) side of the summit.,The surveyed elevation of the mountain and the repeat track elevation data show general similarity but also some differences too. Cloud condition vari
9、ations probably account for most of the observed elevation differences as clouds cause a slower return time for the light pulses relative to a clear sky. This scattering delay causes apparent elevations to be below their true elevations. Work continues to identify and compensate for the impact of cl
10、ouds on ICESats precise altimetry data. Other factors impacting ICESats ability to measure ice sheet features and change are also ongoing.,Measuring Mount Moulton - West Antarctica,Christopher Shuman/NASA GSFC, Laboratory for Hydrospheric Processes, Oceans and Ice Branch (christopher.a.shumannasa.go
11、v),Measuring Mount Moulton - West Antarctica,Feature Name: Mount Moulton Lat: 7603S - Long: 13508W Broad, ice-covered mountain 3,070 m high, standing 10 mi E of Mount Berlin, Flood Range, Marie Byrd Land, West Antarctica,ICESat Track 1322 has been acquired during each GLAS Laser 2 ops period althoug
12、h cloud conditions have impacted data quality/continuity,Measuring Mount Moulton - West Antarctica,The Track 1322 geoid-corrected data are 5 m off of the best summit elevation known and may be offset laterally from the true summit. Gain #s suggest 2b and 2c data was acquired through some cloud cover
13、 around the summit, note vertical exaggeration in plot above).,Feature Name: Mount Moulton Lat: 7603S Long: 13508WBroad, ice-covered mountain 3,070 m high, standing 10 mi E of Mount Berlin, Flood Range, Marie Byrd Land, West Antarctica,Mount Moulton Summit - courtesy of Nelia Dunbar, New Mexico Tech
14、, taken during recent NSF field work,Continuing Rapid Decline of the Arctic Perennial Ice CoverJoey Comiso/NASA GSFC, Laboratory for Hydrospheric Processes, Oceans and Ice Branch (isonasa.gov)The most recent data in the Arctic reveal that for the third consecutive year, the perennial ice cover is an
15、omalously low, especially in the Beaufort, Siberian, and Laptev Seas. This has not happened before during the satellite era and it can be an indication that the ice-albedo feedback is already in full swing. The perennial ice is ice that survives the summer melt and consists mainly of the thick multi
16、year ice cover that resides in the Arctic for as long as 7 years. Because the albedo of open water is so much lower than that of sea ice, more extensive open water area in the summer means more heat is absorbed by the Arctic Ocean and this in turn means a warmer ocean. A warmer ocean would mean earl
17、ier onset of melt, delayed onset of freeze-up and a relatively thinner ice that makes the ice cover even more vulnerable during the melt season. A recovery of the multiyear ice cover is possible but it would require anomalously low surface temperatures for sustained periods during the Arctic summer. Considering that there is global warming going on which is being amplified in the Arctic, this scenario is not likely in the near future. Paper presented at the IGARSS 2004 meeting in Anchorage, Alaska.,
