2. Chapter 16,section 4 Water in the atmosphere By Rachel Kalin, Billy Mahoney Aminata Henderson, Jen Blackey

3. Words to know Psychrometer: An instrument used to measure relative humidity, consisting of a wet-bulb thermometer and a dry-bulb thermometer. Condensation- The process by which a gas, such as water vapor, changes to liquid, such as water. Dew Point- The temperature at which condensation begins. Cumulus- Clouds that form less then 2 kilometers above the ground and look like fluffy rounded piles of cloth. Stratus- Clouds that form in flat layers. Cirrus- wispy feathery clouds made mostly of ice crystals that form at high levels above about a kilometer. Humidity- A measure of the amount of water vapor in the air. Relative Humidity- The percentage of water vapor in the air compared to the maximum amount the air can hold at the temperature. Evaporation- Evaporation: the act or process of evaporating. Evaporating: to change from a liquid or solid state into vapor. 1.to give off moisture 2.to disappear

4. Can you explain to me how relative humidity is measured? Relative humidity is measured with a psychrometer. The psychrometer has two thermometers, a wet-bulb thermometer and a dry-bulb thermometer. The bulb of the wet-bulb thermometer has a cloth covering that is moistened with thermometers. Because the wet- bulb thermometer is cooled by evaporation, its reading drops below that of the dry-bulb thermometer. If the relative humidity is high, the water on the wet bulb will evaporate slowly and the wet-bulb temperature will not change much.

5. What is the difference between relative humidity and humidity? Humidity is a measure of the amount of water vapor in the air and relative humidity is the percentage of water vapor in the air compared to the maximum amount the air could hold. Humidity is the amount and relative humidity is the percentage of water vapor in the air. Why are the tops of some mountains almost always covered by clouds? This happens because when wind strikes the side of a hill or mountain, the air is forced upward. As the air rises along the slope, the air cools. Rain or snow falls on the windward side of the mountains, the side facing the incoming wind.

6. What instrument is used to measure relative humidity? And how does it work? A psychrometer. How does it work? A psychrometer is an instrument for determining atmospheric humidity by the reading of two thermometers, the bulb of one being kept moist and ventilated.

7. How clouds form… Clouds of all kinds form when water vapor in the air becomes liquid water or ice crystals. The process by which molecules of water vapor in the air become liquid water is called condensation. How does water condense? As you know, cold air can hold less water vapor than warm air. As air cools, the amount of water vapor it can hold decreases. Some of the water vapor in the air condenses to form droplets of liquid water. The temperature at which condensation begins is called the dew point. If the dew point is below the freezing point, the water vapor may change directly into ice crystals. When you look at a cloud you are seeing millions of tiny ice crystals or water droplets. Clouds form whenever air is cooled to its dew point and particles are present. But why does the air cool? If air is warmed near ground, it becomes less dense and rises in a convection current.

8. Why are the tops of mountains almost always covered by clouds? This happens because when wind strikes the side of a hill or mountain, the air is forced upward. As the air rises along the slope, the air cools. Rain or snow falls on the windward side of the mountains, the side facing the incoming wind.

9. What conditions are needed for clouds to form? Clouds of all kinds form when water vapor in the air becomes liquid water ice crystals. Clouds form whenever air is cooled to its dew point and particles are present.

10. Three main types of clouds Cirrus- a cloud of a class characterized is thin white filaments or narrow bands and a composition of ice crystals: of high altitude, about 20,000-40,000 ft. Stratus- a cloud of a class characterized by a gray, horizontal layer with a uniform base, found at a lower altitude than altostratus, usually below 8000 feet. Cumulus- A cloud of class characterized by dense individual elements in the form of puffs, mounds, or towers, with flat bases and tops that often resemble cauliflower: as such clouds develop vertically, they form cumulonimbus.

11. Low-level, medium-level, high- level clouds Altocumulus- high-level Altostratus- medium-level Cirrostratus- medium- level Cirrus- high-level Cumulus- low-level Fog- low-level Nimbostratus- low-level Stratus- low-level

12. THE END!!