Rainbows are caused by the splitting of white sunlight into it component colors by raindrops. Some of the light that falls on a water drop enters the drop. As it enters the drop, the light is bent (refracted) and split into a rainbow of colors. This is because each color of light gets bent by a slightly different amount. The different colors then reflect off the back of the drop, and when they pass through the front of the drop again, they are bent (refracted) still more. A rainbow is always directly opposite the sun from the observer. This explains why rainbows are only seen when the sun is low in the sky, usually in the late afternoon. The rainbow's location will appear different for observers at different locations, but it is always directly opposite the sun.
Earth's atmosphere contains certain gases called greenhouse gases (mostly water vapor and carbon dioxide) which act to keep the lower layers of the atmosphere warmer that they otherwise would be without those gases. “Global Warming” is the expected slow, gradual warming of the lower layers of the Earth’s lower atmosphere by the slowly increasing concentrations of man-made greenhouse gases, primarily carbon dioxide, and to a lesser extent methane. These gases trap infrared radiation, which is the “heat radiation” that cools the Earth. (In order for the Earth to remain at a constant temperature, the Earth must lose as much energy through infrared radiation as it gains from the sun. This concept is called energy balance.) The burning of fossil fuels, mainly petroleum and coal, produces carbon dioxide as one of the by-products. As of 2003, the concentration of carbon dioxide is over 50% higher than it was before the start of the industrial revolution in the late 1800's—-which is when the burning of fossil fuels really took off.
How serious will global warming be? We don't know for sure, and there is much debate in the climate research community over this very question. The consensus of opinion is that a warming of about 0.2 degrees Celsius (about 0.4 deg. F) every 10 years is expected for the next 100 years or so. The reason why there is so much uncertainty, though, is because weather acts to rid the surface of the earth of excess heat. The processes by which this happens are very complex, and usually involve water. For instance, clouds (on a whole) act to cool the Earth. How clouds will change with global warming will be critical, as they could either amplify the warming, or reduce it. The evaporation of water removes a huge amount of heat from the Earth’s surface, and this heat is deposited high in the atmosphere when rain clouds form. It is expected that “global warming” will be accompanied by small changes in rain systems. If those rain systems become more efficient at converting water vapor into precipitation, this would act to offset global warming. This is just one of the uncertainties in predicting how much global warming there will be. There are other uncertainties relating to possible changes in sea ice, snow cover, vegetation amount and type, and how much of the extra carbon dioxide will be absorbed by vegetation or by the ocean. How much warming has there been so far? There seems to be pretty good evidence that globally-averaged temperatures have risen about 0.5 degrees Celsius (about 1 deg. F) in the last 100 years. But it is not known how much of this is due to man-made greenhouse gases, or to natural processes. The Earth goes through natural climate fluctuations without any help from mankind. It is reasonable to assume, however, that some portion of the warming in the last century is man-made First, Weather Measurements are Made: Twice each day, radiosondes (weather balloons) are launched all over the world at approximately the same time. They ascend up through the troposphere (the lowest 7-10 miles of the atmosphere, where our weather occurs), and measure temperature, wind, air pressure, and wind speed and direction (through radio tracking or GPS tracking). This information is continuously transmitted back to the ground station, then sent to the National Centers for Environmental Prediction (NCEP) in Washington, D.C. These measurements constitute a global “snapshot” of our weather at one point in time, every twelve hours. Additional measurements are made at surface observing stations (there is probably one near you), on ships at sea, from commercial aircraft, and by weather radars of different types. While different forecasting centers might provide up to four updated forecasts during the day, it is this twice-daily measurement system that leads to only two significantly improved weather forecasts each day.
Next, These Measurements are Put Into Weather Forecast Models All of these measurements are also transmitted to a different weather modeling centers – in the U.S., England, Germany, Australia, and other countries. These modeling centers have very fast supercomputers that have been programmed with equations that describe the interactions between temperature, wind (both horizontal and vertical), and pressure; as well as equations for water vapor transport, the formation of clouds and precipitation; and for the absorption and reflection of solar radiation, and the absorption and emission of infrared (heat) radiation. Together, all of these equations run as a computer program are called a "numerical weather forecast model". Finally, the Interpretation of Model Output: The Forecaster’s Role For many years, weather fcorecast models were not good enough to compute what the weather at the surface would be like…they could only compute the future weather at different levels up through the atmosphere. What happens at the surface (where we live) is very complicated because so much energy is exchanged there, and in a variety of complex ways. For instance, the presence of vegetation greatly cools the surface due to evapo-transpiration--a jungle is much cooler than a desert (but much more humid, too). Forecasters would examine the output from the computer models and would make an educated guess of what the model forecast meant in terms of surface weather. Also, the models were typically biased—under certain conditions, they might habitually make storms too intense, not produce enough rain, etc., -- so these biases had to be factored into the forecaster’s thinking as well "Cyclone" usually refers to an extra-tropical (non-tropical) cyclone, which is a low pressure area that forms near the boundary between warm and cool air masses. As seen above, the cyclone grows in size and intensity as it draws on the energy that is available from the temperature contrast between the two air masses (see below). As some of the warm air rises up over the cold air mass, and some of the cold air sinks and flows under the warm air mass, the cyclone "deepens" (the air pressure becomes lower) and the winds around the system increase. The leading edges of these air masses are called fronts. After a few days, most of the energy that was available to the cyclone is used up, and the cyclone slowly dies. During its lifetime, the cyclone has most likely moved from low latitudes to higher latitudes. In this way cyclones accomplish much of the heat transfer from the tropics to the higher latitudes, and help to maintain the general circulation of the atmosphere. Almost all winter storms are associated with cyclones.
"Cyclone" is also a name given to hurricanes that form in the Indian Ocean. In order to understand why the sky is blue, first we have to understand why some things appear a certain color. Visible light is made up of all colors: red, orange, yellow, green, blue, violet, and everything in between. An object appears "blue" if it reflects (or more accurately, "scatters") more blue light than the other colors of light. For solid objects, those other colors are "absorbed", rather than scattered. For "clear" air, those other colors pass right through, without being absorbed. The sky is blue because the molecules of air scatter some of the blue light, while allowing the other colors of light to pass through. Why blue? Because the size of the molecules of air are close to the wavelength of blue light...about 0.0004 millimeters in diameter. Interesting facts: THE NEXT TIME YOU FLY... When flying in an airplane at 34,000 ft, you are above 75% of the atmosphere. If you look out the airplane window, and look up, you will notice that the sky is a much darker blue than you are used to seeing. This is because you are seeing some sky, but also some of outer space
|