Dust storms carrying tiny particles of minerals from Africa, such as that which hit Israel on Wednesday night, are now arriving throughout the year, and not just during the spring and summer. While there is no solid evidence that their frequency has increased in the past 50 years, some experts predict there will be many more of them in the future due to desertification and global warming. Prof. Joachim Joseph, professor emeritus at Tel Aviv University's department of geophysics and planetary science, told The Jerusalem Post in an interview Thursday that such dust, which settled throughout Israel and was washed out Thursday by the rains, can come from Egypt, the Sahara Desert and even Saudi Arabia, depending on the location of the high winds that lift the dust particles skyward. Israel is not the only recipient of such dust, Joseph said. The dust also levitates north and eastward from Africa to Greece, Turkey and even Switzerland, where a coating of red powder can sometimes be seen in winter on the snow. It can also travel westward to the southern US, Mexico and the Caribbean. It is not sand, which is too heavy to be carried by winds, but smaller dust particles, which are created by erosion of rocks. Research shows that these particles can carry bacteria, spores and even viruses - but these are natural pathogens, not from humans because the source is so hot that nobody lives there. All of the soil in the Beersheba area comes from dust that blew in from Africa, he added. While the dust that flew into Israel can irritate the lungs and airways of young children and people with respiratory disorders such as asthma, the particles usually do not cause serious harm. "They are also beneficial, as they are comprised of minerals, such as iron, that are needed to 'fertilize' the oceans and feed tiny organs on which fish feed. All the sea beds are made of the same particles that lie on the land in the Beersheba region," he noted. Desertification, in which arable land loses rich topsoil because trees are cut down for development, and global warming, in which pollution causes the atmosphere to heat up and water to be lost from the soil, spur the formation of dust particles and their travel thousands of kilometers away. Joseph was in charge of dust experiments on the ill-fated Columbia space shuttle mission, which included astronaut Col. Ilan Ramon, that exploded on reentry to the atmosphere three years ago. Called MEIDEX (Mediterranean Israeli Dust Experiment) the experiment was a success despite the tragic end of the shuttle, as about 70 percent of the data was transmitted to Earth before the scheduled landing and 10% more was collected from surviving pieces of the shuttle. Joseph said that, although the data from one main experiment was completely lost, that which survived provided important information on the course of dust storms from Africa to the Middle East. MEIDEX was the only experiment for which majority of data survived the crash. TAU associate Prof. Colin Price, a colleague of Joseph, added that Wednesday's dust storm, coming in the winter, was "a bit unusual for this time. In the spring and fall, they occur once or twice a month, but in the whole winter, just once or twice in the whole season." "Dust has another beneficial effect - it can seed clouds and increase rainfall production," Price said. While people whose health is sensitive should stay indoors and not exert themselves during dust storms, the particles are "not pollution." "Some may get stuck in the lungs, but eventually they will come out," said Price. "I do not believe they have a major, long-term effect on health."