QuikSCAT satellite showing its age; ASCAT satellite helping out
The now-famous QuikSCAT satellite, which measures winds at the ocean surface world-wide twice per day, was launched in 1999, and has now exceeded its expected lifetime by several years. A reminder of this satellite's age came during the week of November 21-28, when one of the cells on the satellite's battery went bad, forcing engineers to shut off data gathering on the satellite for about 10-15 minutes as it crossed over land in the Arctic. As a result, QuikSCAT provided only half of its usual data on winds and sea ice in the Arctic during that week. Fortunately, engineers were able to swap in a spare battery cell on November 28, and QuikSCAT is now back at full operation. This is good news, since QuikSCAT is a huge help for marine forecasts, sea ice forecasts, and predictions of tropical storms.
QuikSCAT now has help. An important new source of QuikSCAT-like data has been made available by the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT). They launched their first polar-orbiting satellite, Metop-A, in October 2006, and declared the satellite ready for routine operations as of May 2007. This satellite carries a scatterometer called ASCAT which, like QuikSCAT, measures the winds at the ocean surface. ASCAT doesn't "see" the Earth's surface as well as QuikSCAT can--ASCAT sees chunks of the surface 25 km by 25 km, while QuikSCAT has a resolution twice as good--12.5 km. In addition, ASCAT only sees 60% of what QuikSCAT sees of the Earth's surface--QuikSCAT sees a swath of ocean 1800 km wide, while ASCAT sees two parallel swaths 550 km wide, separated by a 720 km gap. I found it frustrating to use ASCAT much this hurricane season, since it seemed that the passes missed the center of circulation of a storm of interest about 75% of the time.
Figure 1. Comparison of the coverage pattern of the QuikSCAT and ASCAT satellites, from December 4, 2007. Image credit: NOAA.
However, ASCAT has an important advantage--it can measure ocean surface winds where heavy rain is occurring, something QuikSCAT cannot. Both instruments carry an "active" radar (also called a scatterometer)--an instrument that emits a pulse of microwave energy that bounces off the ocean surface and returns to the satellite. The amount of microwave energy bounced back to the instrument is inversely proportional to how rough the sea surface is, and one can compute the wind speed and direction at the ocean surface based on this information. QuikSCAT uses microwave energy with a wavelength of about 2 cm (Ku-band), which is significantly affected by heavy rain. Microwave radiation from ASCAT uses a wavelength of about 5 cm (C-band), which is much less affected by rain. Thus, ASCAT can retrieve winds more accurately in the heavier precipitation environments such as those found in hurricanes. However, QuikSCAT does have finer spatial resolution and better sensitivity to high winds than ASCAT. Another minor advantage of ASCAT is that the winds across the entire swath of ocean it looks at are of uniform accuracy. QuikSCAT, on the other hand, has a bit larger errors at the edge of its 1800 km-wide swath, and in the middle, making it more difficult to interpret the data in some cases.
QuikSCAT data is routinely ingested into all of the major computer models that forecast hurricanes. ASCAT data is not yet used in this way, since ASCAT is currently still in its calibration and validation phase. However, by the 2008 hurricane season, ASCAT data will probably be used in this fashion. Having ASCAT to complement QuikSCAT will be a big help to NHC forecasters, particularly for those storms far out at sea where the Hurricane Hunters cannot reach.
ASCAT data is available from the ASCAT web page. QuikSCAT expert Dr. Paul Chang of NOAA also has ASCAT data available on his NOAA Marine Observing Systems web page.
Next blog
This Friday, the Colorado State University team issues its first forecast for the 2008 Atlantic hurricane season. I'll present an analysis of the forecast Friday afternoon.
Jeff Masters
Reader Comments
Page: 1 | 2 | 3 | 4 | 5 — Blog Index
Daman seems to undergo an eyewall replacement cycle, the structure as become quite asymetrical over the past hours. In the first frames of the water vapor loop you can still see the former well-organized storm with a clear eye which collapses in the next frames. At the end of the loop I think I see a new eye forming. I'll be out for some hours now, let's see how Daman looks like then.
I'm quite happy that the cyclone did not take the forecast track over the island but seems to miss it. This one is really unpredictable. Yesterday the forecast still called for a passage between the two bigger islands, then it had the storm going over the island and now it circles it to the east.
Public Information Statement
Statement as of 7:00 am EST on December 7, 2007
The governors of Virginia and North Carolina have declared the week
of December 2nd to 8th... 2007 winter preparedness week. The National
Weather Service offices serving Virginia and North Carolina... in
cooperation with their respective departments of emergency
management... will send public information statements each day
through Saturday at approximately 7 am. These statements will focus
on different aspects of winter weather... and preparedness actions
the public should take for the upcoming winter season.
Today's topic: heavy snow.
For most of the last 10 Winters... temperatures have been normal to
above normal. What will this winter bring? The National Weather
Service outlook for this winter is calling for below normal
temperatures and near normal precipitation across the commonwealth.
Weak El Nino conditions in the equatorial Pacific Ocean are expected
to play a role in this winter's weather... by producing a stronger
than normal southern jet stream called the subtropical jet. Storm
systems intensifying rapidly along the eastern Seaboard during the
colder months of the year are usually responsible for producing most
of the heavy snows in our area.
These systems... called nor'easters... can also produce strong winds
which may result in blizzard conditions and huge snow drifts. Heavy
snow tends to occur 100 to 150 miles to the northwest of the track
of the surface low. Snow amounts well in excess of 30 inches have
occurred with nor'easters in our area. In addition... strong winds
and very cold temperatures can result in blizzard or near blizzard
conditions... dangerous wind chill values... and have resulted in snow
drifts up to 12 feet high.
The exact track the surface low pressure takes and how much cold air
is in place ahead of the system... determines if and where heavy snow
will occur. Given that cold air is in place... a surface low that
travels a hundred miles or so off the coast can produce some snow in
the central portion of Virginia and North Carolina... with the
potential for heavy snow confined to the eastern portions of the
area. If the surface low travels along the coast or slightly
inland... heavy snow is most likely in the northwestern one third of
Virginia.
If the amount of cold air in place is marginal for snow... it is
possible that heavy wet snow could occur in the higher elevations
with just a cold rain in the lower elevations. Heavy snow is capable
of bringing down tree limbs and power lines which may result in
power outages. In rare instances... heavy snow may result in the
collapse of roofs of buildings and homes. In addition... heavy snow
may result in snow covered or ice covered roads. This typically
leads to vehicle accidents and potentially major traffic jams. If
there is enough heavy snow and... or wind... some roads may be closed
and other roads may only be successfully traversed by 4 wheel drive
vehicles.
The following is a summary of historic snowstorms in virginia:
February 14-18 2003. 7 to 36 inches of snow across central and
northern Virginia (highest far north)... significant ice southern
Virginia.
January 24-25 2000. 6 to 19 inches of snow across much of central
and eastern Virginia.
January 6-7 1996. 12 to 30 inches of snow in much of
western... central... and northern Virginia. A few locations in the
mountains received over 3 feet of snow. Twenty four hour snowfall
records were established at Roanoke and Lynchburg. In
Virginia... there was one fatality directly attributed to the storm.
In the mountains... strong winds on January 8th created snow drifts
up to 10 feet high.
March 12-15 1993. 20 to 30 inches of snow with some amounts over 3
feet in the mountains. In the foothills... 10 to 18 inches of snow
fell. In Virginia... there was one fatality directly attributed to
the storm. In the mountains... strong winds up to 50 mph whipped
drifts up to 12 feet high and created near blizzard conditions.
February 10-12 1983. 10 to 20 inches of snow in a large portion of
Virginia with up to 30 inches of snow in northern portions of the
state. The storm established 24 hour snowfall records at
Roanoke... Lynchburg... and Richmond.
March 5-8 1962. 10 to 24 inches of snow in many interior portions of
Virginia.
Being prepared means making good decisions based on information
contained in outlooks... watches... warnings... advisories... other
statements and forecasts from the National Weather Service. The key
is to know what to do in advance. If a winter storm like what
occurred in 1993 or 1996 was predicted to hit Virginia in two
days... what would you do between now and when the storm arrives to
get ready? You should make sure you have enough food... water and
medication for several days. You also need to be prepared for the
loss of power and... or heat.
Up to date weather information is available at:
Www.Weather.Gov/Blacksburg
The National Weather Service winter weather awareness home Page is
found here:
" " " " " " " " " " " " "" " " "
Much of N.C schools systems are under a 2 hour delay/closed where I live.Not one weather station predicted ice/snow.Though weatherunderground said a 20% of freezing rain above 3000f.t. We had ice down around 1000f.t and below.
When the met came on air this morning he said the "Alberta Clipper diped more south than expected".None of the roads were treated this morning with salt.
We had like 2 clippers this week. Some schools have been closed/delayed 2 or three times.
Weak El Nino conditions in the equatorial Pacific Ocean are expected
to play a role in this winter's weather...
HUH?
204. NorthxCakalaky 4:36 PM GMT on December 07, 2007
Weak El Nino conditions in the equatorial Pacific Ocean are expected
to play a role in this winter's weather...
Did I miss something the past couple of weeks?
no offense, but better you than me :o)
And people move south to escape the cold... it will track you down, it will!
Afternoon, NE, Storm...everyone else..
merked out there for a while, children's breakdowns....
Be careful of the two very popular weather terms El Nino and La Nina. They are as much TV hype terms as anything.
I think hes in NW NJ...
Link
bone's about to get his dose pretty soon...
I think hes in NW NJ...
Yeh,most of the activity has been down toward his area.
April cant come soon enough!
Viewing: 201 - 219
Page: 1 | 2 | 3 | 4 | 5 — Blog Index