Weather

Weather and Climate Weather denotes a short term behavior of the earths atmosphere – Hours to a week – Applies to a local area – Rain, warm, windy et al. Climate refers to a long term condition and describes weather in broad parts of the world

Meteorology The science of atmospheric processes and phenomena – From the Greek meteoros meaning “high in the air” – Meteorologist – one who studies meteorology

All starts with sun

Solar Radiation

Perihelion and Aphelion

The path of the earth around the sun

Temperature Lags

Seasons

Sun at Latitudes

Atmosphere

Three Cell Circulation

Layers of the Earths Atmosphere Troposphere is the lowest layer – Extends from earths surface to about 5 miles – troposphere is heated by solar energy absorbed by the earths surface and reradiated at infra-red wavelengths – Note temperature highest near the heat source Thin air is not as heavy as cooler air to the north and south of the equator – Thus a permanent area of low pressure is established on the equator – This intense heat also drives a great deal of evaporation in equatorial oceans which creates a permanent band of cloudiness at low latitudes (ICTZ)

Surface at the Poles The earths surface gets very cold near the poles – Cold polar surface cools the troposphere – A kilogram of cold air fills a smaller volume than hot air – so the volume of the air at the polar troposphere shrinks and the air becomes thicker – The troposhere’s shrinking volume sets up downward vertical currents – just the opposite of the situation above the equator – Air sinks above the poles

Pressure Gradient Forces PGF is caused by the difference between the weight of air above the pole and the weight of air above the equator Creates a closed circuit in that cold polar air slides along the earths surface toward the equator and warm air from equator slides poleward aloft to replace it. Since “weight” is caused by the earths pull acting on the mass of the air PGF is a manifestation of gravity

Three Cell Circulation Rotation of the earth causes this simple circuit to change in two ways – The PGF is counter balanced by the Coriolis Effect also known as Horizontal Deflection Force – The simple Hadley Cell circulation is broken into three parts Permanent low pressure is on the surface at the equator and 60 degrees north and permanent high pressure on the surface at 30 degrees and on the poles

Wind flows from the polar highs southward to the sub polar lows (60 degrees north) and is deflected to the west. These permanent winds are called the Polar Easterlies Wind flows from the subtropical high (30 degrees north) northward to the sub polar low and is deflected to the east. These are called the Prevailing Westerlies Wind flows from the subtropical high southward to the Equatorial Trough and is deflected to the west. These permanent winds are called the Trade Winds