Water in the Atmosphere

Water in the Atmosphere

Characteristics of Water solid state at 0 o C or below (appearing as ice, snow, hail and ice crystals) liquid state between 0 o C and 100 o C (appearing as rain and cloud droplets) gas state 100 o C or higher. This is an invisible gas referred to as water vapor.

Characteristics of Water energy is either absorbed or released when water changes state changing from a gas to a liquid is called condensation, energy is released. Products of condensation are dew, fog, and clouds condensation slows down the rate at which air cools changing from a liquid to a gas is called evaporation, energy is absorbed. Evaporation is a cooling process, heat is absorb by water molecules

Humidity Humidity: amount of water vapor present in the air. Specific Humidity: actual amount of water vapor in the air at a given time or place is. Expressed as the number of grams of water vapor per kilogram of air. Relative Humidity is what meteorologist report in weather forecasts. Relative humidity is how near the air is to maximum capacity holding water vapor. Relative humidity units is percentage (%) for

Humidity Saturated: when air cannot hold anymore water vapor Amount evaporating equals the amount of condensation forming Amount of water vapor in saturated air is dependent on the temperature. The warmer the air the more water vapor it can hold. The water vapor capacity of air roughly doubles for every 11 o C rise in temperature.

Measuring Humidity Humidity measured using a psychrometer and a relative humidity chart. The psychrometer, works on the principle that evaporation causes cooling. A psychrometer consists of two thermometers, one dry bulb and one wet bulb.

Condensation Condensation is the changing of water vapor to a liquid night air cools more rapidly and when it cools past the point of saturation, condensation occurs. Water vapor condensing in the atmosphere forms clouds or fog. Water vapor condensing on surfaces is called dew. Dew Point is temperature at which saturation occurs and condensation begins. The more water vapor in the air the less the air has to cool in order for condensation to begin.

Cooling and Condensation Two conditions are required for condensation to occur: 1. Condensation nuclei 2. Air must cool to or below the dew point Condensation nuclei are usually substances such as salt, sulfate, particles, or nitrate particles. Condensation nuclei are also required for the formation of ice crystals. Air may cool or lose heat through the following ways: Contact with a colder surface Radiation of heat Mixing with colder air Expansion as it rises

Cooling and Condensation (cont) Dew/Frost forms when moist air contacts a colder surface. Air temp above 0 o C dew forms Air temps below 0 o C frost forms Fog forms when air cools through contact and mixing Droplets are so small they fall slowly so that the slightest air movement keeps them suspended. At very cold temperatures fog may consist of ice crystals. Radiation fog occurs when the nighttime sky is clear and the ground loses heat rapidly (common in humid valleys) Advection fog occurs when warm moist air blows over a cool surface.

Clouds Four types of clouds Low clouds Middle clouds High cloud Vertical developed clouds classified based on their altitude and shape. Cloud names formed from one or more of five words or word parts: Stratus or strato clouds that form in layers Cumulus and cumulo clouds that grow upward, puffy Cirrus and cirro feathery clouds Alto clouds located between 2000 and 7000 meters Nimbus and nimbo dark rain clouds

CLOUDS

Cloud Formation Shape of a cloud shows how the air is moving Vertical developed clouds form when rising air is lighter than the surrounding air. condensation level: the atmospheric level at which condensation occurs Rising air cools to its dew point Without a steady influx of warm, moist air the cloud will soon evaporate. clouds stop growing upward when the air in the cloud reaches the same temperature as the air surrounding the cloud.

Cloud Formation (cont) the adiabatic rate is the rate at which air cools. water vapor releases energy (heat) as it condenses. released heat is very important to the formation of clouds Rising dry air cools faster than rising moist air. Moist air cools more slowly due to the fact that heat is being released by condensing water vapor. Heat released during condensation can fuel the growth of huge cumulonimbus clouds.

Cumulonimbus Clouds Cumulonimbus clouds form as moist air rises and cools to its dew point (condensation level). Heat released from the condensation keeps the air rising. air inside the cloud is warmer and less dense than the air outside. cumulus clouds that receives continuous supply of warm moist air continues to grow until it enters a layer of stable air. Stable air is where the surrounding air temperature is the same as inside the cloud.

Layer Clouds Stratiform or layered clouds form in stable air. Air cannot easily move up or down in stable air so the clouds spread out horizontally. Clouds form in stable air in two ways: Air is forced slowly upward to its condensation level. This happens when air moves up a mountainside or over a layer of colder denser air or a low pressure forces it upward. Air can cool past its condensation level by radiating heat or mixing with cooler air

Predicting Condensation Level As air rises the temperature and the dew point decreases. condensation level can be determined by knowing the ground temperature and dew point Knowing the condensation level allows for predicting at what level clouds will form predicting how high they will grow. predicting the severity of a possible storm

Precipitation Precipitation: any form of water that has formed in clouds and has grown heavy enough to fall to Earth. Water droplets grow by bumping into and combing with other water droplets. the larger the droplets the faster they will fall. temperatures in upper clouds is below freezing both ice and supercooled droplets form in the clouds supercooled droplets evaporate and deposits on the ice crystals causing them to grow

Kinds of Precipitation There are several forms of precipitation: Drizzle, Rain, Snow Sleet: rain freezes as it falls Freezing rain: rain freezes as it hits a cold surface Hail: balls or irregular clumps of ice. In the summer, frozen precipitation melts before hitting the ground except for Hail. Hailstones begin as a frozen raindrop or small, dense clump of ice crystals Strong updrafts cause hailstones to grow until it is too heavy to stay aloft The stronger the updrafts the larger the hailstones.

Where does precipitation occur rising and cooling moist air major cause of precipitation warmer the air is before it rises more moisture it can hold the higher air rises the more precipitation it can release Areas that receive the most precipitation are those where warm moist air rises high in large quantities.s Near the equator due to heating of the land by insolation, causing warmed air to rise. Daily thunderstorms Low pressure areas which cause air to rise and cool to produce precipitation Areas where moist air often blows across a mountain range, the windward side receives precipitations as the air rises and cools. It can receive large amounts of precipitation. the leeward side the colder and dryer air is sinking and warming so there is little to no precipitation on this side of the mountain range (desert regions occur on the leeward side of a mountain range).

Windward and Leeward

Global Precipitation