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Using Rita
Jamais Cascio, 26 Sep 05

vorticity.jpgThere's been a flurry of understandable attention of late about the relationship between global warming and hurricanes. Climate scientists have emphasized that the number of storms this season -- unusually high, so much so that we may run out of storm names and have to move to Greek letters -- is still within the historical context of the Atlantic Multidecadal Oscillation, or "hurricane cycle." There's not much evidence that the increased sea surface temperatures have resulted in more storms. Instead, climate science suggests that the effect of warmer oceans is two-fold: heated water expands, so warmer oceans mean higher storm surges; and, as hurricane strength is primarily driven by ocean surface temperatures, warmer seas can mean stronger storms. A number of recent studies, both historical and model-based, have shown this relationship, and you can find more detail on the relationship between hurricane intensity and global warming here.

As a result of this increased attention to storm intensity, research agencies around the world are putting more effort into better observations and forecasts of hurricane strength. This week, both the American National Center for Atmospheric Research (NCAR) and the European Space Agency (ESA) have announced ongoing storm intensity projects. NCAR is using this year's hurricane season as a test of their new Weather Research and Forecasting model, known as ARW, while the ESA has turned its Envisat network to watch North Atlantic hurricanes, providing novel insights into the inner workings of hurricane Rita. Both organizations are making their work available to the public over the web.

The NCAR work focuses on their latest methodology for predicting storm intensity, the ARW model.

With its high-resolution grid of data points just four kilometers (about 2.5 miles) apart, the model can project the location of fine-scale rainbands and eyewall structures 72 hours into the future. [...]

Teams supporting the Department of Energy and Department of Homeland Security are using real-time ARW data in their damage models. The researchers are testing how computer simulations of a particular hurricane's most destructive features might improve damage model projections and lead to better warnings of floods, power outages, and road blockage. This year's test cases have included hurricanes Katrina, Ophelia, and now Rita.

One particularly interesting aspect of ARW is that its forecasts are available to anyone over the web as more than processed, static reports. The ARW page at the Weather Research & Forecasting website allows visitors to choose various parameters (from resolution to air conditions) and model run dates -- you can even select past dates to compare with real-world results. For those who don't want to fiddle with the model settings, a number of "Quick Look" items can be easily accessed: continental US precipitation; surface air temperature, with a focus on the Gulf of Mexico region; and wind speeds along the Gulf coast. All images are for 18 hour forecasts.

Better forecasting has obvious value for disaster response efforts. Being able to predict accurately the intensity and path of a storm allows for pre-positioning of units, timelier evacuation orders, or even the ability to avoid unnecessary evacuations. Moreover, while the NCAR work is currently focused on the United States, improved forecasting models would have even greater utility for nations without either the geographic size to move out of the way of a storm or the resources to respond effectively on their own. Being able to put out a call for help before the worst has happened can save many lives.

Improved forecasting models rely on better real-world data, and the ESA's Envisat satellites have been pointed at Hurricane Rita, providing exactly that. In particular, the Envisat systems have been providing heretofore unseen levels of detail about storm-wide wind speeds and system temperatures. Although "hurricane hunter" aircraft can provider even greater detail, their flights are limited by storm behavior, and can't get the whole system in a single shot.

Envisat carries both optical and radar instruments, enabling researchers to observe high-atmosphere cloud structure and pressure in the visible and infrared spectrum, while at the same time using radar backscatter to measure the roughness of the sea surface and so derive the wind fields just above it.

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

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

One of the more interesting systems carried by Envisat is the "scatterometer," which uses a cluster of radar bursts to measure ripples on the ocean surface, giving both speed and direction of wind. The Envisat scatterometer can cut through heavy rains, so it can get accurate surface wind speeds even in the strongest of storms. According to the ESA, the Envisat scatterometer is the only system of its kind in orbit.

As with much of the ESA data, select photos and radar images are available for download at high resolutions, including the Hurricane Rita eye, scatterometer wind data, and full-system photos of the storm.

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