ATMS 120 1st Edition Lecture 3 Outline of Last Lecture I General temperature variations II Seasonal variations in temperatures III Seasons the effects of latitude IV Proximity to large bodies of water V Vertical temperature variations Outline of Current Lecture I Pressure II Pressure measurement barometer A Relationship between atmosphere and temperature III Barometer and surface pressure IV Pressure variations it s why the wind blows Current Lecture I Pressure is the force per unit area applied by air This is equivalent to the weight of the air in a column over an area such as a square inch Pressure is measured in units called millibars mb Some typical pressure values Average sea level pressure 1013 25 mb 14 7 pounds per square inch PSI 29 92 inches mercury In Champaign Illinois the highest recorded pressure was 1045 mb In Champaign Illinois the lowest recorded pressure was 980 mb In general the lower the pressure the worse the weather For example hurricanes occur in lower than normal pressure II Barometers use liquid mercury in a dish with a vacuum like effect The barometer will read at 29 92 in during average atmospheric pressure As atmospheric pressure increases it pushes on the mercury in the dish driving the mercury in the glass tube up past 29 92 in A The thickness of the atmosphere changes based on the temperature An application of this is pilots who need to adjust their flying altitude based on the temperature in which they are flying in to balance out the pressure These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute III Low pressure is associated with bad weather while high pressure is associated with nice weather Low surface pressure of less than 1000 mb results in clouds precipitation and unsettled weather High surface pressure of greater than 1000 mb results in fair weather IV There is a very close relationship between wind and pressure Vertical Air pressure decreases rapidly with height This is balanced by gravity Horizontal Air moves because of horizontal pressure differences Always moves from higher pressure to lower pressure The greater the change in pressure over a given distance the faster the wind Most important takeaway message of the lecture
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