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Confronting Iraq:
Weather and War

With Stephen Davenport from Dubai, UAE
Meteorologist, Weathernews, Inc.

Wednesday, March 26, 2003; 11 a.m. ET

Weather can affect war. Tuesday, Air Force Maj. Gen. Victor Renuart said at a press briefing at U.S. Central Command headquarters in Doha, Qatar that it was not "a terribly comfortable day on the battlefield" because of sandstorms that limited visibility and tormented the troops. Gen. Richard B. Myers, chairman of the Joint Chiefs of Staff, admitted in a TV interview that "the weather has played a factor, but those sorts of things are factored in. We understand the weather over there and when it gets really bad, then we have to slow down a little bit, but it will not stop the operation."

The extreme types of weather found in the Gulf region are completely unlike what most Americans have experienced. Predicting sandstorms -- their duration, their height, the impact on visibility -- can help the military understand the situation faced by the troops in the field. Forecasting marine weather can impact the military's weather-sensitive activities like diving and supply boat operations. And the longer the battle, the more weather will play a part because the region will become significantly hotter in the very near future.

Stephen Davenport, meteorologist for Weathernews, Inc., located in Dubai, United Arab Emirates, was online Wednesday, March 26 at 11 a.m. ET, to discuss weather and climate conditions in the Gulf region.

Weathernews, Inc. is the world's largest weather company which provides weather information, analysis and decision support products and services to businesses in industries like agriculture, aviation, energy, marine, media, mobile and offshore oil.

A transcript follows.

Editor's Note: Washingtonpost.com moderators retain editorial control over Live Online discussions and choose the most relevant questions for guests and hosts; guests and hosts can decline to answer questions.

Vienna, Va.: Can you give us the weather forecast for Baghdad for the next couple days?

Stephen Davenport: There’s going to be a vast improvement in Baghdad's weather, and indeed across Iraq as a whole. The strong southeast winds have ended, although right now a strong westerly is bringing further sandstorms with visibility down to less than a mile and as low as 100 or even 50 yards in exposed spots. A few scattered showers are passing though, too, but any rain will clear and the wind is going to quickly drop Thursday morning with skies then clearing and the haze lifting. As an added benefit, and something of a relief, it’s going to be a noticeably cooler, too, with temperatures in the 60s for a while rather than the 80s.

NW Washington, D.C.: Has the weather in the Gulf region been in the normal range it usually is since the war started or is it different now?

Stephen Davenport: The Gulf's weather hasn't been especially unusual for March. We're coming to the end of winter and towards the spring transition phase before the full blast of summer, and this is often the time of year when weather systems become most active. This can partly be explained by the interior of the Arabian Peninsula beginning to heat up while colder air over the northern hemisphere's middle latitudes can still penetrate south and southeast through Europe and Asia Minor. This "clash" of air masses causes discontinuities very like standard weather fronts and they can become very active. Having said all that, the freqency of these storms has, at a guess, been a little greater than normal due to a "blocking" high pressure system over Europe forcing weather systems around to the north and then south towards Arabia.

Bethesda, Md.: How far ahead can you forecast weather conditions?

Stephen Davenport: We like to think we can be confident in our predictions up to about five days ahead but we can and do forecast up to 10 days in advance. This is, of course, with the caveat that the further into the future we look the less confident, naturally, we can be. Anything more than that is of little operational use, although studies and comparisons of past weather can allow estimates of month-long outlooks. Confidence in the forecast also depends on comparing different computer models -- if they are not in agreement then we tread more carefully.

Washington, D.C.: Do the U.S. and British commands get their weather information from you?

Stephen Davenport: No, they have their own meteorologists, some of whom, as I understand it, are trained in combat situations and are present near the front lines.

New York, N.Y.: Will these sandstorms actually affect and possible ruin some of the equipment of the U.S. soldiers?

Also, are these sandstorms seasonal? If yes, when will they be over? How long til the weather turns warm enough to hinder the soldiers in Iraq?

Stephen Davenport: It's conceivable, although I am sure that the military is very well prepared for these eventualities -- and I'm no expert on armaments! What I do know is that, however well you think you have covered up, sand and dust particles can find there way into every nook and cranny -- including the eyes, ears, nose, throat and lungs.

Sandstorms can be at their worst at this time of year when particularly active depressions develop nearby -- as happened during the last few days. However, there is also a period in the summer where a steady north to northwest wind can keep sand on the move. This can last, approximately, from late May through June and into July and can get strong enough to cause sandstorms. It's known as the "40-day Shamal". The "Shamal" is simply the local name for the north to northwest wind, from the Arabic for "north."

The heat would eventually become a problem. Average daytime maximum temperatures rise from 79 F in March to 90 F in April, 102 F in May, 108 F in June and 113 F in July and August -- and those are shade temperatures.

Glen Burnie, Md.: Are these sandstorms in Iraq really of "historic" proportions as discussed in today's Post?

Stephen Davenport: From my own experience of 10 years in the Gulf region I'm not too sure about that, although I have no direct experience of conditions in Iraq itself. I am sure that there have been times when the wind has been as strong (30 to 40 mph) and therefore would expect there to have been similar sandstorms in the past.

Georgetown, Washington, D.C.: I understand that the evironment differs radically across Iraq -- desert around Basra; verdant in the Euphrates valley below Bagdad.

Do the sandstorms carry over into the lusher areas like one of our hurricanes, or peter out as soon as they hit trees?

Also, do Bagdad drivers freak out as soon as there's a drop of rain like they do here in D.C?

Stephen Davenport: There would be very little sand rising from the lusher regions as the vegetation tends to hold the topsoil together. However, dust in suspension in the air can travel many, many miles and reduce visibility over a very large area. Where I am sitting in Dubai, the city has become very green and of course it is crowded with buildings but recently we have had a couple of periods of very thick dust haze from particles carried from the surrounding desert.

Alexandria, Va.: How does a sandstorm start?

Stephen Davenport: Taking a desert, for example, it's basically an uneven surface comprising many millions of particles of sand and dust held in place by their own weight. If there is no wind then they stay in place but when the wind gets in motion those particles can start to vibrate and move. The wind speed at which this starts to occur depends to a degree on the size of the particles and their composition. However, once the wind threshold is reached those particles can be carried from the surface into the windflow; they then fall back and disturb more particles which in turn get caught by the wind and so the process continues, especially if the wind also strengthens further.

There are three processes by which particles are carried, depending on their size, density and shape. Firstly 'suspension' which involves particles (dust) less than 0.1 mm in diameter; these can be carried for thousands of miles and rise as high as 3 or 4 miles, and although they reduce visibility they do not really comprise a sandstorm. Secondly there is 'creep' which involves particles generally greater than 0.5mm in diameter but still small enough to be carried. These scurry along the surface and help to form sand dunes, and pile-ups of sand on roadsides, etc. In between are, thirdly, 'saltating particles' which can be lifted into the air and what you might encounter in a sandstorm. They rarely rise higher than about 10 feet.

Washington, D.C.: The sand seems to be different colors when you see it on television. Is that because it's at different times of day? Is it like a dirt sand?

Stephen Davenport: It could partly be due to the time of day or to the density of the sandstorm, if you are referring to the lifted sand. There are also different shades depending on local geomorphology -- near the coast I think it is paler, as this could be sand mixed with salt from evaporated sea-water (sometimes known as 'sabka' locally). The redder sand might be stained by iron oxide from millions of years of water running through the mountains to the north.

Dixon, Calif.: What is the depth of the atmospheric sand during a sandstorm created by average winds of 40 mph? 100 meters? 300 meters? 500 meters? Does the concentration of sand particles vary in the vertical by a log-scale or is it homogenous? How about in the lower 100m compared to the 100m-500m layer?


Stephen Davenport: The finest particles can rise as high as 40 to 50 miles and be carried for thousands of miles around the globe. However, those would be exceedingly fine particles, of the order of 0.001 mm diameter. They can remain in suspension for between 1 and 10 years. Closer to the surface, dust particles of 0.01 mm can rise about 800 yards, while fine sand of 0.1 to 0.5 mm rises to head-height or a little above as stays suspended for only a few seconds. There is some variation in that depending on the strength of the wind but much depends on the precise size, density and shape of the particles. The concentration is not homogenous but nor am I sure, as you interestingly ask, that it is strictly logorithmic.

Washington, D.C.: So have we seen the worst of the sandstorms for this week?

Stephen Davenport: Yes, the worst are over for this week -- or at least they will be by the end of the Iraqi night (Wednesday 26th night into Thursday 27th morning). It's going to feel a lot cooler, fresher and more comfortable, too. The northwest wind bringing that better weather might pick up a little towards the weekend but nowhere near the strength we've seen the last two or three days.

McLean, Va.: The Gulf area seems like a pretty open region. Is that true and if so, does it affect the weather they get there?

Stephen Davenport: To a degree that's true. The lands to the east, south and north are fairly flat but do gradually incline inland. That would make the Gulf a kind of shallow bowl, and indeed the waters are relatively shallow across much of its area. However, one long edge is bounded by Iran and the Zagros mountains which rise to heights of 10,000 feet about 150 miles inland. One effect of this geology is for subsiding air to "drain" towards the Gulf and cause strengthening winds, especially with 'lee troughs' often forming just on the southern edge of the Zagros mountains. This is one reason for the '40 day Shamal'. One other reason is the semi-permanent 'heat low' which forms towards summer over the 'Empty Quarter' -- the southern Saudi Arabian desert.

College Park, Md.: What causes sand berms to form?

Stephen Davenport: Strictly speaking a 'berm' is formed on a beach by wave action, often a deposition of sand above the normal tide level by an earlier storm or storms. It slopes up from the water to a nearly flat top. 'Dunes' such as those found in parts of the Iraqi desert are by definition formed by wind action. Sand particles are blown up one side of an irregularity in the desert's surface and fall down the lee side where the wind is lighter due to the shelter. Dunes continue to grow as varying winds push sand particles to different degrees up the slope. Some reamin on the windward side while others are carried to the top and are dropped as the wind becomes lighter on the lee side. By this method dunes can also travel in the prevailing wind direction -- albeit very slowly indeed over many years -- as material is picked up from the windward side and deposited on the lee side.

Stephen Davenport: That's all from me for now. Thank you for your questions, and my apologies if I didn't get to yours. I hope I've been able satisfactorily to answer those I am able. For more information on Weathernews, Inc. and its partner companies, please log on to www.us.weathernews.com, www.wni.com, www.oceanroutes.com and www.oceanroutes.co.uk

© 2003 The Washington Post Company