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Good morning. It’s good to see so many of you taking an interest in meteorology. As you are all newcomers to the topic, let’s keep it simple to start with. ha fact, let’s begin with a very simple definition of what meteorology is—the suffix ’ -logy ’ gives you a clue—at least you can all guess that it is’ the study of ’...something. Meteorology is in fact the scientific study of all changes in the atmosphere—essential for forecasting the weather, of course. And you all know what weather is, right? The four main ingredients are...the sun, the atmosphere, water vapor and the wind. They all come together, disseminating heat from the sun around the globe and making clouds in the layer of the atmosphere directly above the ground which is called the troposphere. Look up into the sky and on almost any day of the year you’ll see clouds.
    Clouds form when water that has evaporated from the surface of the Earth condenses onto microscopic dust particles (or other particles ) floating in the air. Cloud formation takes different shapes and they mostly get their names from Latin roots. Now, let’s look at the five most basic. We’ll start with Cumulus which is a low cloud with a white, puffy appearance and most often composed of water droplets. It gets its name from  ’ cumuli’ meaning  ’ heap’ for its typical ’piled-up’ appearance.
    Now, let’s move on to Stratus (from  ’ strata’ meaning  ’ layer’ )—these are the grey, horizontal ones (often with a fiat base) that you see on an overcast day and they too are mostly made up of water droplets. At this point, I should mention Fog, which you probably don’t even think of as clouds, but fog consists of very low stratus—ground-hugging clouds. The high altitude Cirrus cloud, on the other hand is mostly made of ice crystals and appears wispy and thin—almost hair-like—in fact, that’s where they get their name...from the word ’cirri’ meaning ’wisp of hair’. They are generally fair-weather clouds.
    Not so the Cumulonimbus—the tallest of all clouds—they extend way up into the troposphere and these are the ones that produce lightning, thunder, heavy rain, strong winds and tornadoes. Beware the Cumulonimbus! You already know what cumuli means and it won’t surprise you to find out that  ’nimbus’ means  ’rain’ and, added as a suffix, is an indication of the cloud’s ability to produce precipitation which could be rain, snow or hailstones.
    As this course progresses, you’ll learn a lot more about cloud types but before I finish today, I want to go back to something I mentioned before—dust. It is generally accepted that when water vapor ascends in the process of cloud formation it condenses onto dust particles. So, it was assumed, large dust particles would produce larger droplets and enhance the formation of rain. However, recent research has shown the opposite to be true. Droplet size increases the farther the clouds are from dust-filled air. More dust reaching rain clouds produces less rainfall. Scientists have shown that as more and more dust enters a rain cloud, the same amount of water becomes spread out. The resulting smaller water droplets scatter instead of combining and growing large enough to make up raindrops.
    This study shows that higher dust frequency is not inevitably the result of diminished rainfall but rather its cause! Therefore, loss of topsoil from over-grazing, over-cultivation or bad livestock management in areas neighboring desert will contribute to the continuing expansion of those arid regions.
    Your assignment for this week will be to read up on this research and write a report on how dust from damaged land may exacerbate drought conditions and lead to further desertification of arid areas. In other words, how land use has an impact on climate change.