Chapter 6 and 7: Properties of the Atmosphere AND Weather Systems

Origin and Structure of the Atmosphere: Erupting volcanoes – outgassing – put a lot of water vapor, CO2 and Nitrogen in the air during the early years of the Earth. Eventually, photosynthetic organisms put Oxygen into the air. The atmosphere is divided into layers (see p. 14 in the ESRTs) based on temperature differences.

Changes in Air Pressure: Altitude, temperature and humidity differences create air pressure differences. When altitude increases, the pressure decreases. (see p. 14 in ESRTs!!) When temp increases, pressure also decreases! When humidity increases, pressure ALSO decreases.

Moisture in the atmosphere: When air is “filled” to its capacity with water vapor, it is saturated. If the air is cooled to its dewpoint it is saturated. So, air that is the most humid either has: –A- a lot of moisture that have evaporated into the air OR –B- been cooled to its dewpoint.

Measuring Moisture: A psychrometer (wet-and dry-bulb thermometer) is used to measure relative humidity and dewpoint. Use the charts on p. 12 in the ESRTs! Don’t forget: You must remember to subtract the wet-bulb temp from the dry-bulb temp. If there is a difference of “0” between the wet- and dry-bulb temps, the R.H. is 100% and the air temp is AT D.P.!

What Causes the Wind? Unequal heating and the resulting air pressure differences result in wind. When the air is heated (like over the land area during a summer day) it rises. Cool areas (like over the water during the DAY) have higher pressure and the air sinks. Winds blow from high pressure to LOW! Thanks to wind, our world has more moderate temps. The “wind” helps to even out the energy around the world.

The Coriolis effect occurs due to the Earth’s rotation. This makes the winds curve as they blow! (see p. 150 in the rev. bk) The jet stream general info can be found on p. 150 in the rev. bk and on p. 14 in the ESRTs. Prevailing winds are also on p. 14 in the ESRTs.

What is weather? Meteorologists study changeable atmospheric conditions to make weather predictions. See p. 152 for info on how weather variables are related. Clouds form when a series of different events occurs: –Air rises –Air cools…. (see next slide for more)

Air cools to its DEWPOINT! Once at the dewpoint, water vapor can go through condensation and form droplets on tiny “condensation nuclei” – little bits of stuff in the air. Voila! A cloud! Why does air cool as it rises? –Higher altitude = fewer air molecules. –Expansion of the air molecules = adiabatic cooling. –This is why a CO2 cartridge gets COLD after being used!

How does energy enter the atmosphere? Energy from the sun comes in the form of “electromagnetic radiation” – primarily via visible light. When this energy strikes the Earth, a LOT gets used just to make water evaporate! See p in the rev. bk. For great illustrations!

What is a Synoptic Weather Map? Station models are used to display LOTS of weather info. (See p. 13 in the ESRTs for an example!) The info from many, many station models can be used to draw in isolines – like isotherms (temp), isobars (air pressure), etc. We can track the movement of air masses on weather maps.

Air Masses are defined by their temp and moisture content. (c or m? P, T or A?) The leading edge of vastly different air masses creates fronts. The front symbol (warm? Cold?) shows the direction the front is moving! To predict the weather, meteorologists look for High or Low pressure areas moving toward a region. (Generally from the WEST to the EAST in the continental US)

High pressure = nice, clear, maybe a little cool weather. Low pressure = cloudy, unsettled, maybe stormy weather. The weather at fronts also tends to be unsettled because there is low pressure occurring at fronts! Why? Because when warm and cool air meet, the warm air will rise. Rising air = low pressure! (see p. 170 in the rev. bk!)

Natural Hazards Know the safety advice for the storms listed and described on p