Meteorology

Formation and Composition of Early Earth’s Atmosphere The atmosphere was formed from eruption of gases from volcanoes The early atmosphere contained little oxygen and more CO2 than the modern atmosphere. Early photosynthetic life generated oxygen and consumed carbon dioxide No life existed on earth until the ozone formed, this layer absorbs ultraviolet radiation.

Today’s Atmosphere The earth’s atmosphere is 21% oxygen, 78% nitrogen, and 1% trace elements. The atmosphere of venus is mostly CO2 and very dense. The martian atmosphere is very thin and mostly CO2.

What affects the atmosphere? Human activities have increased CO2 content in the atmosphere. Man made chemicals have decreased ozone concentration in the upper atmosphere. Volcanic activity and meteorite impacts can eject large quantities if dust and gases into the atmosphere. The ability of earth’s atmosphere to absorb and retain heat is affected by the presence of gases like water vapor and CO2.

Water and the atmosphere Water occurs in 3 states (solid, liquid, and gas). Temperature differences produce differences in density, which produce convection.

Layers of the atmosphere All weather is contained in the troposphere. The stratosphere contains the protective ozone.

Energy transfer and convection Convection is a current that is set up when hot, less dense material rises, cools, becomes less dense and sinks Convection is a major mechanism of energy transfer in the ocean and the atmosphere. Convection in the atmosphere is a major cause of weather. The energy transfer from convection between the earth’s surface and the atmosphere creates weather.

Energy transfer cont. The surface of the earth is more efficiently heated by the sun than the atmosphere. The amount of energy reaching any given point in the earth’s surface is controlled by the angle of sunlight striking the surface and varies with the seasons. Areas near the equator receive more of the sun’s energy per unit than areas nearer the poles.

Weather Weather describes day to day changes in atmospheric conditions. Climate describes the typical weather patterns for a given location over a period of many years.

Climate There are 4 forces that affect climate Latitude Elevation Proximity (closeness) to bodies of water Position relative to mountains

Atmospheric Pressure Pressure is caused by the force of gas molecules. Air pressure is greatest near sea level and lessens as you move up from sea level. The instrument used to measure air pressure is a barometer The most common units to measure air pressure are millibars

Wind Wind direction and the speed is measured with a wind vain or a anemometer. Wind is created by uneven heating at the earth’s surface and modified by the pressure differences. Wind direction is given as the direction wind blows. Wind blows from high to low pressure.

Coriolis Effect It is created by the rotation of the earth. The coriolis effect causes the wind to curve to the right in the northern hemisphere and to the left in the southern hemisphere. The coriolis effect helps to create global wind systems.

Wind Systems Jet streams (strong winds) blow at the top of the troposphere.

Daily and Seasonal Wind Small wind systems determine the local weather.

Sea Breeze Sea breezes are created during the day because solar radiation warms the land more than the water.

Land Breeze Land breeze- air moves towards the water.

Humidity The amount of water vapor held in the air

Relative Humidity The measure of the amount of water vapor in the air, compared to the maximum it can hold at a specific temperature

Saturated Condition when air contains as much moisture as possible at a specific temperature

Dew Point The temperature at which air is saturated with water and condensation begins

Fog A stratus cloud that forms on or near the ground when air is cooled to its dew point and condenses

Precipitation Water or ice that condenses in the air and falls to the ground as rain, snow, sleet or hail, depending on the temperature.

Clouds Clouds form as warm moist air rises. As the air rises in the atmosphere it expands and cools. When the temperature of the rising air mass reaches 100% relative humidity then water vapor begins to condense around particles of dust, salt, or smoke called condensation nuclei. These droplets are so small that they can be suspended in air by wind currents. Millions of these droplets can collect, forming clouds.

Types of clouds There are three types of clouds based on shape and height.

Stratus Clouds Stratus clouds form smooth layers that cover the sky in sheets. These clouds are associated with both fair weather and long steady rainfall.

Cumulus Clouds Cumulus clouds are puffy. White, puffy, clouds are associated with fair weather, but he towering dark puffy clouds are associated with thunderstorms.

Cirrus Clouds Cirrus clouds are thin, “wispy” very high clouds. These are usually associated with fair weather, but might indicate that the weather is about to change.

Naming Clouds Prefixes are used to indicate how high the base of the cloud is. Cirro means high elevation (above 6000 m) Alto means medium elevation ( 2000-6000 m) Stratus means low elevation (under 2000 m). Nimbus in the name means that it is a rain cloud.