Featured Research

from universities, journals, and other organizations

Envisat And ERS-2 Reveal Hidden Side Of Hurricane Rita

Date:
September 23, 2005
Source:
European Space Agency
Summary:
As Hurricane Rita entered the Gulf of Mexico, ESA's Envisat satellite's radar was able to pierce through swirling clouds to directly show how the storm churns the sea surface. This image has then been used to derive Rita's wind field speeds. Notably large waves are seen around the eye of Hurricane Rita in the radar image.

This zoom from a larger Envisat ASAR image shows the signal return from the sea surface beneath the eye of Hurricane Rita. It was acquired in Wide Swath Mode early on 22 September UTC and has a resolution of 150 metres. The image measures 100 x 75 km.
Credit: ESA

Notably large waves are seen aroundthe eye of Hurricane Rita in the radar image. ASAR measures thebackscatter, which is a measure of the roughness of the ocean surface.On a basic level, bright areas of the radar image mean higherbackscatter due to surface roughness. This roughness is stronglyinfluenced by the local wind field so that the radar backscatter can beused in turn to measure the wind.

So the Center for SoutheasternTropical Advanced Remote Sensing at the University of Miami used thisASAR image to calculate the speed of Hurricane Rita's surface windfields – showing maximum wind speeds in excess of 200 kilometres perhour.

"The most detailed information about hurricane dynamics andcharacteristics are obtained from dedicated flights by hurricane hunteraircraft," explains Hans Graber of CSTARS. "However these flightmissions cannot always take place. Satellite remote sensing provides acritical alternative approach.

"It is critical for weatherforecasters to obtain reliable characterization of the eye walldimension and the radii of gale- tropical storm- and hurricane-forcewinds in order to provide skilful forecasts and warning. Satellitebased observations will facilitate better understanding of hurricaneevolution and intensification.

"Radar images penetrate throughclouds and can easily detect the eye replacement cycle of hurricaneswhich are precursors to further intensification."

Rita was amaximum Category Five on the Saffir-Simpson Hurricane Scale when theASAR image was acquired. As it continues west through the Gulf ofMexico it has weakened to a still-dangerous Category Four. Rita isexpected to make landfall on the Gulf coast during the morning of 24September.

ERS-2 joins in Rita observations

Thesame day Envisat acquired its ASAR image of Rita, its sister spacecraftERS-2 also made complementary observations of the hurricane'sunderlying wind fields using its radar scatterometer.

Thisinstrument works by firing a trio of high-frequency radar beams down tothe ocean, then analysing the pattern of backscatter reflected upagain. Wind-driven ripples on the ocean surface modify the radarbackscatter, and as the energy in these ripples increases with windvelocity, so backscatter increases as well. Scatterometer resultsenable measurements of not only wind speed but also direction acrossthe water surface.

What makes ERS-2's scatterometer especiallyvaluable is that its C-band radar frequency is almost unaffected byheavy rain, so it can return useful wind data even from the heart ofthe fiercest storms – and is the sole scatterometer of this typecurrently in orbit.

The ERS-2 Scatterometer results for HurricaneRita seen here have been processed by the Royal NetherlandsMeteorological Institute (KNMI). They are also routinely assimilated bythe European Centre for Medium-Range Weather Forecasting (ECMWF) intotheir advanced numerical models used for meteorological predictions.

"Scatterometerdata from the ERS-2 platform provide high-quality wind information inthe vicinity of tropical cyclones," states Hans Hersbach of ECMWF. "Fora Hurricane like Rita, the combination of such observations with[in-situ] dropsonde data enables the analysis system at ECMWF toproduce an improved forecast."

NOAA using Envisat radar altimetry data

AnotherEnvisat instrument called the Radar Altimeter-2 uses radar pulses tomeasure sea surface height (SSH) down to an accuracy of a fewcentimetres.

Near-real time radar altimetry is a powerful toolfor monitoring a hurricane's progress and predicting its potentialimpact. This is because anomalies in SSH can be used to identify warmerocean features such as warm core rings, eddies and currents.

TheUS National Oceanic and Atmospheric Administration (NOAA) is utilisingEnvisat RA-2 results along with those from other space-borne altimetersto chart such regions of 'tropical cyclone heat potential' (TCHP) andimprove the accuracy of Hurricane Rita forecasting.

Observing hurricanes

Ahurricane is basically a large, powerful storm centred around a zone ofextreme low pressure. Strong low-level surface winds and bands ofintense precipitation combine strong updrafts and outflows of moist airat higher altitudes, with energy released as rainy thunderstorms.

Envisatcarries both optical and radar instruments, enabling researchers toobserve high-atmosphere cloud structure and pressure in the visible andinfrared spectrum, while at the same time using radar backscatter tomeasure the roughness of the sea surface and so derive the wind fieldsjust above it.

Those winds converging on the low-pressure eye ofthe storm are what ultimately determine the spiralling cloud patternsthat are characteristic of a hurricane.

Additional Envisatinstruments can be used to take the temperature of the warm oceanwaters that power storms during the annual Atlantic hurricane season,along with sea height anomalies related to warm upper ocean features.


Story Source:

The above story is based on materials provided by European Space Agency. Note: Materials may be edited for content and length.


Cite This Page:

European Space Agency. "Envisat And ERS-2 Reveal Hidden Side Of Hurricane Rita." ScienceDaily. ScienceDaily, 23 September 2005. <www.sciencedaily.com/releases/2005/09/050923153256.htm>.
European Space Agency. (2005, September 23). Envisat And ERS-2 Reveal Hidden Side Of Hurricane Rita. ScienceDaily. Retrieved July 24, 2014 from www.sciencedaily.com/releases/2005/09/050923153256.htm
European Space Agency. "Envisat And ERS-2 Reveal Hidden Side Of Hurricane Rita." ScienceDaily. www.sciencedaily.com/releases/2005/09/050923153256.htm (accessed July 24, 2014).

Share This




More Earth & Climate News

Thursday, July 24, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Goma Cheese Brings Whiff of New Hope to DRC

Goma Cheese Brings Whiff of New Hope to DRC

Reuters - Business Video Online (July 24, 2014) The eastern region of the Democratic Republic of Congo, mainly known for conflict and instability, is an unlikely place for the production of fine cheese. But a farm in the village of Masisi, in North Kivu is slowly transforming perceptions of the area. Known simply as Goma cheese, the Congolese version of Dutch gouda has gained popularity through out the region. Ciara Sutton reports. Video provided by Reuters
Powered by NewsLook.com
Bill Gates: Health, Agriculture Key to Africa's Development

Bill Gates: Health, Agriculture Key to Africa's Development

AFP (July 24, 2014) Health and agriculture development are key if African countries are to overcome poverty and grow, US software billionaire Bill Gates said Thursday, as he received an honourary degree in Ethiopia. Duration: 00:36 Video provided by AFP
Powered by NewsLook.com
Higgins Breaks Record at Mt. Washington

Higgins Breaks Record at Mt. Washington

Driving Sports (July 24, 2014) Subaru Rally Team USA drivers David Higgins and Travis Pastrana face off against a global contingent of racers at the annual Mt. Washington Hillclimb in New Hampshire. Includes exclusive in-car footage from Higgins' record attempt. Video provided by Driving Sports
Powered by NewsLook.com
Storm Kills Three, Injures 20 at Virginia Campground

Storm Kills Three, Injures 20 at Virginia Campground

Reuters - US Online Video (July 24, 2014) A likely tornado tears through an eastern Virginia campground, killing three and injuring at least 20. Linda So reports. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

    Health News

      Environment News

        Technology News



          Save/Print:
          Share:

          Free Subscriptions


          Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

          Get Social & Mobile


          Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

          Have Feedback?


          Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
          Mobile: iPhone Android Web
          Follow: Facebook Twitter Google+
          Subscribe: RSS Feeds Email Newsletters
          Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins