Stories tagged forecasting

Jun
25
2010

Adios El Niño, Hello La Niña?: The Pacific has switched from warm (red) to cold (blue).
Adios El Niño, Hello La Niña?: The Pacific has switched from warm (red) to cold (blue).Courtesy NASA

How to measure ocean temperature

There are many ways to measure the temperature of an ocean. Oceans are big and temperatures at different locations vary. To get a sense of whether the ocean is warming or cooling, lots of spread out measurements need to be made.

  • Thermometers under buoys or ships Since about 1990 an extensive array of moored buoys across the equatorial Pacific Ocean has beamed temperature data from a 1 meter depth up to a satellite. Lots of ships are also recording their intake water temperatures but the depths and locations vary making this data harder to use.
  • Satellite remote sensing NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) SST satellites have been providing global SST (Sea Surface Temperature) data since 2000. Unlike buoys, the satellites can sense the surface temperature everywhere. The temp measured is of the surface only, though. The surface "skin" temp can be quite different than the temp of the water below because of things like evaporation, wind, sunshine, and humidity. Also, cloud cover prevents satellites from sensing surface temperatures.
  • Acoustic Tomography Sound, especially low frequencies, can travel long distances under water. Since the speed of sound under water varies with temperature, measuring how long sound takes to travel a certain distance will give you the average temperature of the water over that distance. Acoustic Thermometry of Ocean Climate (ATOC) is using trans-basin acoustic transmissions to observe the world's oceans, and the ocean climate in particular.
  • Ocean Surface Topography By bouncing microwaves off the the ocean surface and using GPS location, satellites can precisely measure the height of any spot on the ocean surface. Reasoning that water expands and contracts as it heats and cools, then so too would the height of the sea surface. I think Ocean Surface Topography is the easiest and best technique for measuring ocean temperature.
    In a 2005 study researchers compared satellite measurements of sea surface height in the northeast Pacific Ocean from 1993-2004 to recordings of sea surface temperature in the region during the same period. The sea surface height measurements proved to be as accurate as temperature measurements as indicators of ocean conditions resulting from long-term climate cycles as well as being more consistent. PhysOrg

El Niño and La Niña effect on hurricanes

Ocean temperature information is useful in predicting hurricane season severity and forecasting individual storm severity. The image above shows that the Pacific Ocean is changing from hot to cold.

A La Niña is essentially the opposite of an El Niño. During a La Niña, trade winds in the western equatorial Pacific are stronger than normal, and the cold water that normally exists along the coast of South America extends to the central equatorial Pacific. La Niñas change global weather patterns and are associated with less moisture in the air, resulting in less rain along the coasts of North and South America. They also tend to increase the formation of tropical storms in the Atlantic.

"For the American Southwest, La Niñas usually bring a dry winter, not good news for a region that has experienced normal rain and snowpack only once in the past five winters," said Patzert. NASA

The National Oceanic and Atmospheric Administration (NOAA) has issued its Atlantic hurricane season forecast. The prediction -- "near-normal" -- fits pretty well with the forecasts from AccuWeather, Colorado State University, WSI Corporation, and the Weather Research Center. What does "near-normal" mean? NOAA is predicting 9 to 14 named storms, with 4 to 7 hurricanes, and 1 to 3 major storms (category 3 or higher on the Saffir-Simpson scale of storm intensity).

But storm prediction is a tricky business. More rainfall over West Africa, warmer sea surface temperatures, and reduced wind shear could encourage more storms. An El Nino pattern in the Pacific or cooler ocean temperatures could discourage them. NOAA will issue another prediction in August, just before the usual peak in the hurricane season.

Jul
10
2007

So said Yogi Berra, and science is proving him right. It turns out that making accurate predictions entails more than taking current conditions and extrapolating them into the future. It’s a specialized sub-field of mathematics, with lots of rules to ensure that predictions have a reasonable chance of being accurate.

Scott Armstrong of the University of Pennsylvania and Kesten Green of Monash University, Australia, examined the forecasts recently made by the UN’s Intergovernmental Panel on Climate Change.

Armstrong and Green rated the methodology used by the panel against 89 principles of good forecasting derived from years of research. They found that the panel report breached 72 of those principles. They concluded that the forecasts the weather was likely to change in many negative ways were worthless.

Now, this doesn’t mean that the Earth isn’t getting warmer—that’s a well-established fact. But, most of the predictions we’ve heard of climate catastrophe due to this warming are based on bad math.

(Freeman Dyson, physics professor at Princeton, makes a similar point in this video. He argues there’s been too much focus on building computer models of climate, and not enough emphasis on collecting actual data to see if the models hold up.)

May
25
2005

The United States Geologic Service has launched a website which shows the probability of an earth-shaking event in any spot for California over the next 24 hours. The model is most useful in predicting aftershocks — small tremblers that follow a large quake. Those large quakes remain almost impossible to predict. But knowing if an aftershock is due will help Californians prepare their homes and keep damage to a minimum.

Earthquakes occur when two pieces of the Earth's crust collide, divide, or scrape past one another. The dividng line between two such pieces is called a fault line. Many fault lines run through California, so they have lots of earthquakes. Minnesota has no fault lines, so earthquakes here are very rare.

Read more about earthquake forecasting