by Bob Henson
Thunderstorms develop on the coast of Hawaii’s Big Island. (Photo by Carlye Calvin.)
What do February’s deadly wildfires and scorching heat in southeast Australia have to do with rainfall in the tropics? Duane Waliser (Jet Propulsion Laboratory) and Mitchell Moncrieff (NCAR) hope to find out. Waliser and Moncrieff are chairing the science planning group for the Year of Tropical Convection. YOTC’s goal is to better predict the behavior and effects of massive clusters of showers and thunderstorms that regularly prowl Earth’s low latitudes and influence weather elsewhere.
“Our shortcomings in predicting tropical convection severely limit the representation of key physics in weather and climate models,” says Waliser. On the plus side, he adds, “The tropical atmosphere-ocean-land systems have never been so well observed.”
YOTC, which is actively seeking collaborators, is pooling observations collected across the tropics during a “year” that actually extends from May 2008 through September 2009. These include data from several major field campaigns held across the Pacific in the last few months (see “On the Web”). YOTC is also archiving global analyses and forecasts at high resolution (25 kilometers/16 miles) from the European Centre for Medium-Range Weather Forecasts. Many other global and regional models will likely be woven in, along with ultra-high-resolution cloud-system-resolving models.
With these tools in hand, participants will look at ways in which forecast skill might be significantly improved by 2012. The goals include better short-to-medium-range forecasts of tropical weather as well as enhanced medium-to-extended-range predictions at midlatitudes, where tropical influences often reverberate.
Australia offers a recent example. Even as parts of the state of Victoria experienced severe drought and record temperatures as high as 48.8°C (119.8°F), which stoked wildfires killing more than 200 people, the state of Queensland has been dealing with floods that inundated an area larger than Texas.
“I suspect these things are connected,” says Moncrieff. “Of course, we don’t know exactly what the full connection is, but that’s one of the events we’re going to target.” One important player was a Madden-Julian Oscillation (MJO) event, an organized cluster of convection that pushed southward from Indonesia into northern Australia over several weeks in January after gathering strength in the Indian Ocean. Weather systems spawned by the slow-moving MJO not only brought heavy rains to Queensland but apparently helped induce drying and subsidence on its southern flank, including the Melbourne area.
Along with scrutinizing MJOs, YOTC is also studying:
- easterly waves, which roll westward with the trade winds and can develop into tropical cyclones
- monsoonal variations, including the timing of the monsoon’s onset as well as breaks within the rainy season
- tropical climatology, including such factors as rainfall distribution, the diurnal cycle of convection, and the average location and strength of the Intertropical Convergence Zone
YOTC is sponsored by a number of global weather entities, including the World Meteorological Organization, the World Climate Research Programme, the World Weather Research Programme, and its THORPEX experiment. The science planning group includes more than 20 tropical specialists from the United States, Europe, Australia, and Asia.
Word about YOTC is spreading, with an article now in the works for the Bulletin of the American Meteorological Society. This July, at an implementation meeting, planners will choose weather and climate events to be analyzed in case studies. “The data gathering ends in September, but the research will go on for a long time,” says Moncrieff.