Weather wing fights the dust

OFFUTT AIR FORCE BASE, Neb. -- In the early months of 2003, while most were anxiously awaiting the first signs of spring, things were heating up fast for troops in Iraq. Plans for a ground-attack on Baghdad were in place.

Less than a week shy of the date of execution, the troops received news that drastically changed their plans.

"The 28th Operational Weather Squadron accurately predicted a dust storm five days in advance," said William T. Sedlacek, 16th Weather Squadron meteorologist. "The forecast substantially mitigated negative impacts on the mission. In fact, the advanced warning enabled the Air Force to exploit the dust storm to its advantage through the utilization of GPS-guided munitions and heat-detecting gun sights, which are unaffected by reduced visibility."

Had it not been for the accurate prediction by the 28th OWS Airmen, the outcome may have been considerably different.

"Dust storms are capable of reducing horizontal and vertical visibility to near zero, leading to aborted missions, disorientation of troops on the ground and in the air, and potential collisions between aircraft," said Sedlacek. "In fact, dust was likely a contributing factor in the deadly collision between a transport plane and helicopter during an attempted rescue of U.S. hostages in Iran in 1980. Additionally, fine dust particles settle into machinery, weaponry, computers, and electro-optical systems, leading to further mission disruptions."

While the operational weather squadrons are responsible for the predictions, the 16th WS has the duty of creating tools to make the predictions possible.  The first step is understanding what creates a dust storm.

"Most people assume strong winds pick up dust from the ground, but a little known fact is that while it is possible for wind to directly lift dust into the air, that is not the primary physical mechanism seen in nature," said Glenn Creighton, 16th WS meteorologist. "This is because dust particles, typically clay or silt, are very tiny and cling well to each other and do not easily lift off the surface."

However, after winds pick up to around ten miles per hour, larger particles, typically sand, which are less 'clingy,' begin to creep and then bounce over the ground in a phenomenon called saltation, he added. 

"As the large particles come crashing down, they effectively 'sandblast' the surface, breaking up clumps of smaller particles and jettisoning them into the air," Creighton said. "These smaller particles do not settle back to the ground so quickly, and can be lifted up many kilometers into the atmosphere by strong vertical winds at the leading edge of a frontal boundary."

So how is this information used to create prediction tools?

"Over the last five years, the 16th WS has vastly improved dust modeling by moving away from a two model approach to an integrated atmosphere-chemistry model called Weather Research and Forecasting - Chemistry," Creighton said. "In conjunction with WRF-CHEM experts at the National Center for Atmospheric Research and National Oceanic and Atmospheric Administration's Earth System Research Laboratory, the 16th WS created a new dust emission scheme within the WRF-CHEM model.  The scheme accounts for the effects of soil moisture, vegetation, soil composition, and sand blasting intensity on dust emission."

Once the emission model lofts the dust into the modeled atmosphere, the numerical weather model does the rest of the work to move it around, continued Creighton.

"In its efforts to improve the physics of its dust model, the 16th WS also partnered with the Desert Research Institute to obtain one of the highest resolution dust source region databases in the world," Creighton said. "This dust source region database supplies the emission model with its most critical piece of information:  'how much dust is available to be lofted into the atmosphere?'  Today, the 16th WS runs the WRF-CHEM model within its Mesoscale Ensemble Prediction Suite, a computationally powerful ensemble of weather models that produces not only dust, but other conventional, aviation, and severe weather forecasts for the U.S. Armed Forces."

Although these models are state of the art, at the end of the day, prediction still relies heavily on the human factor as well.

"Forecaster experience is crucial to predicting dust storms," Creighton said. "Numerical weather models are not perfect, and forecasters have to take their experience and observations from field personnel into account in addition to what the models say.  Forecasters are very good at pattern recognition, and they can fall back on past experiences to give them guidance for a given weather pattern."

Nevertheless, efforts to keep improving are still underway.

"Looking ahead,  the Air Force anticipates collaboration with the United Kingdom Met Office and the U.S. Army's Cold Regions Research and Engineering Laboratory on additional dust forecasting capabilities, including potential utilization of the next generation United Kingdom Chemistry and Aerosols model," Sedlacek said.