WEATHER & THE ATMOSPHERE A. Weather - the conditions of the variables of the atmosphere for any short period of time Meteorology - the study of weather and weather related variables - the variables: Topic 1 p. 477 TQ 1ab p. 483 1. Air Temperature a. depends on the intensity and duration of insolation received by an area b. measured with a thermometer 2. Air/Atmospheric/Barometric Pressure - the force exerted by the column of overhead a. measured with a 3. Atmospheric Moisture/Humidity a. measured with a hygrometer 4. Wind Speed and Direction a. wind speed measured with an b. wind direction measured with a 5. Atmospheric Transparency - a measure of how clean and the air is a. depends on the number of aerosols, pollutants (natural and man-made) and amount of cloud cover at the time the measurement is made - its value varies as time passes Facts about weather related variables: 1. all these variables interact in the - the lowest portion of the atmosphere 2. the relationship between these variables is very complex. 3. the relationships are expressed as a probability of occurrence - very few occur with 100% certainty 4. accurate weather predictions are difficult to make - especially those made more than 36 hours in advance 5. changes in the weather are caused by the uneven distribution of insolation/heat energy within the atmosphere - it varies indirectly with latitude B. The atmosphere gains energy four ways: Page 1 of 11
1. The Greenhouse Effect - carbon dioxide and water vapor trap outgoing rays released by the Earth s surface 2. Direct absorption of insolation - 19% mentioned in previous topic 3. Change of Phase reactions - condensation and sublimation release stored latent heat energy into the atmosphere 4. Conduction from the lithosphere - the warm ground releases heat into the air NOTE : all the energy gained by the atmosphere is distributed throughout the atmosphere by C. Adiabatic Temperature Changes - a change in the temperature of the air due to or with no loss or gain of heat energy Topic 10 p. 487 TQ p. 490 10abc, Topic 12 pp. 508-509 TQ p. 511 12abc 1. as air rises, it, its volume, so there is now more area to be heated by the same amount of heat energy - temperature [as a result] 2. as air sinks, its, its volume, so now there is less area to be heated by the same amount of heat energy - temperature [as a result] 3. there is a 10 C change in temperature for every kilometer dry air changes its elevation 4. there is a 6 C change in temperature for every kilometer moist air changes its elevation a. there is a 4 C difference because in moist air condensation or sublimation are releasing stored latent heat energy into the air, slowing the cooling process (-10 +4 = -6 ) D. Air/Atmospheric/Barometric Pressure - the force exerted by the column of air overhead Topics 1,2,3,4 pp. 523-525 TQ s p. 526 1ab not c, 2b not a, 3ac not bd, 4ab 1. it averages 14.7 lbs/in 2, 1013 millibars, or 29.92 inches of mercury 2. air pressure values are influenced by: Page 2 of 11
a. air temperature - as air temperature increases, air density, so air pressure b. elevation above sea level - as elevation increases there is less air overhead so air pressure c. moisture content of the air - as air becomes more moist, heavy nitrogen molecules are being replaced with lighter water vapor molecules so air density and air pressure E. Wind Speed and Direction Wind - the movement of air to the Earth s surface - the horizontal Topic 6 p. 527 TQ p. 530 6ab Facts about wind: 1. winds are caused by differences in air between two locations 2. winds are caused by the unequal of the Earth s atmosphere - this results in differences in air 3. winds always move from areas of pressure towards areas of pressure 4. winds always move from areas of divergence towards areas of convergence 5. winds are named for where they come, NOT for where they are going 6. surface ocean currents are caused by energy transfer from winds to water 7. wind direction in influenced by the coriolis force Topic 9 p. 529 TQ p. 530 9abc a. winds are deflected to their in the northern hemisphere b. winds are deflected to their in the southern hemisphere 8. wind speed depends on the - the numerical difference in air pressure between two locations divided by the map distance between these two locations a. pressure gradients are expressed by the spacing of isobars on a weather map 1. an isobar is a line of equal b. as the distance between isobars increases (as they get further apart) the pressure gradient and the wind speed Page 3 of 11
9. Special winds Topic 7 pp. 527-528 TQ p. 530 7a not b p. 527 28.6 a. seabreeze/onshore wind - during the day, land heats faster than the sea - air pressure over the warmer land falls and cooler, more air from over the sea rushes in - air moves from the sea towards the land b. landbreeze/offshore wind - during the night, land cools faster than the sea - air pressure over the land rises and this cooler, more dense air from the land rushes out to sea - air moves from the towards the F. Planetary Wind and Pressure Belts Topics 13&14 pp. 532-533 TQ s p. 534 13 bc not a 14 abcef not d 1. at 0 &60 latitude, there is generally low air pressure, low air density, so air 2. at 30 &90 latitude, there is generally high air pressure, high air density, so air 3. at 0 &60 latitude, at the Earth s surface, winds blow towards one another, these are called areas of 4. at 30 &90 latitude, at the Earth s surface, winds blow away from one another, these are called areas of 5. Prevailing winds - geographic zones on the Earth s surface where winds tend to move in the same direction as measured over long periods of time a. from 30 North to 60 North (USA) the prevailing wind direction is from the southwest - called the prevailing b. weather systems in the United States tend to move from southwest to northeast under the influence of the prevailing 6. Jet Streams - a narrow zone of very strong winds in the upper troposphere Topic 17 p. 536 TQ p. 537 17abc p. 537 28.16 a. usually located over 40 North latitude although they migrate north in summer and south in winter p. 536 28.15 b. they tend to steer weather systems across the country from west to east G. Atmospheric Moisture Water vapor enters the atmosphere two ways: Topics 1&2 p. 499 TQ s p.502 1abcd,2ab 1. evaporation - a change of phase from a liquid to a at moderate temperatures 2. transpiration - plants release directly into the air Page 4 of 11
3. evapotranspiration - a combination of terms - the process whereby water vapor enters the atmosphere a. this requires the addition of energy to occur b. this water vapor carries a lot of potential energy (latent heat) into the atmosphere There are 4 factors that influence the rate at which water vapor enters the air: 1. air temperature - as air temperature increases, evapotranspiration increases 2. surface area - (how spread out the water is) - as surface area increases, evapotranspiration 3. air circulation/wind - as air circulation increases, evapotranspiration 4. moisture content of the air/humidity - as humidity increases, evapotranspiration (the air is already holding a lot of water vapor and doesn t have room for much more) H. Atmospheric Moisture Terminology 1. Saturation - when the air is holding all the water vapor it can hold a. this occurs when the air temperature is cooled to the dewpoint temperature b. at saturation, dynamic equilibrium exists and the amount of water vapor entering the air through evaporation is to the amount of water vapor leaving the air through condensation 2. Capacity - the maximum amount of water vapor the air can hold a. it depends on air temperature, directly 3. Absolute/Specific Humidity - a measure of the actual amount of in a given volume of air Topic 3 p. 500 TQ p. 502 3abc 4. Relative Humidity - the ratio between actual humidity and how much water vapor is in the air compared to the amount the air can contain Topics 4&5 pp. 500-501 TQ s p. 502 4ab, 5abcd a. it s expressed as a % b. if the relative humidity is 65% - the air is holding 65% of what it could hold there s room to hold 35% more than it is holding Page 5 of 11
There are 3 factors that influence relative humidity values: a. air temperature - as air temperature increases, capacity. If no new water vapor enters the air but the air can now hold more, relative humidity b. time of day - relative humidity is lowest in the mid-afternoon when temperatures are highest relative humidity is highest in the early morning when temperatures are c. absolute humidity - if more water vapor enters the air while temperature remains the same, relative humidity 5. Dewpoint Temperature - the temperature to which the air must be cooled before: Topic 6 p. 503 TQ p. 505 6abcde a. it becomes b. it reaches its maximum capacity c. it reaches 100% ( ) d. condensation or sublimation begins Facts about dewpoint temperature: a. it s measured in C b. it s measured with a - a combination of a dry bulb and wet bulb thermometer c. it depends on the actual amount of water vapor in the air - the the dewpoint temperature, the greater the amount of water vapor in the air - values are high in summer and low in the winter Topic 8 p. 504 TQ p. 505 8 d. if the dewpoint temperature is above freezing and saturation occurs, condensation will begin and liquid water droplets will begin to form in the air or dew on the ground e. if the dewpoint temperature is below freezing and saturation occurs, sublimation will begin and snow flakes/ice crystals will begin to form in the air or frost on the ground 6. Dry Bulb Temperature - the same as 7. Wet Bulb Temperature - the temperature recorded by a thermometer whose alcohol Page 6 of 11
reservoir is wrapped in a piece of saturated cloth a. it s always lower than or equal to the dry bulb temperature b. evaporation of water from the cloth draws heat away from the alcohol and the level falls c. if the air is saturated (100%RH) NO can take place and the wet bulb temperature will be the same as the dry bulb temperature 8. Wet Bulb Depression - the difference between the dry and wet bulb temperatures a. it s used to calculate dewpoint temperature and relative humidity I. Clouds and Precipitation Cloud - a collection of tiny liquid water droplets and/or ice crystals which remain suspended in the atmosphere Topics 10&11 pp. 506-507 TQ s p. 511 10ace, not b or d, 11 a. clouds are NOT made of water vapor b. condensation and sublimation cause clouds to form Condensation nuclei - tiny particles in the atmosphere around which liquid water droplets or ice crystals collect Topic 7 p.p. 503-504 TQ p. 505 7abc a. rising, moist air with condensation nuclei present is the recipe for clouds Precipitation - the falling of or water from clouds towards the Earth s surface Topics 16&17 pp. 512-514 TQ s p. 517 16abcd, 17abc a. there are 4 types of precipitation : rain, snow, sleet, hail - fog, dew, and frost are NOT precipitation b. precipitation cleans the air - it enhances atmospheric transparency - it brings condensation nuclei from the air to the Earth s surface Page 7 of 11
c. precipitation cannot occur unless the water droplets/ice crystals grow large enough to fall under their own weight - not all clouds bring precipitation even though all clouds are made of tiny water droplets or ice crystals p. 512 27.12 d. without condensation nuclei there can be no precipitation - there s no surface for the droplets/ice crystals to collect and grow on Topic 21 p. p. 515-516 TQ p. 517 21ab 1) cloud seeding is an attempt to introduce artificial condensation nuclei into clouds to make the droplets/crystals grow in size e. precipitation is associated with the passage of a front through an area J. Air Masses - a large body of air in the troposphere with similar,, and values throughout Topic 5 pp. 525-526 TQ p. 526 5ab Topics 1,2,3 pp. 543-544 TQ s p. 546 1ab, 2abcde, 3ab a. wind speed and direction vary within an air mass b. weather predictions are based on air mass movements There are 2 basic types of air masses: 1. Cyclone - Low Pressure Center - Convergent Air Mass Topic 8 pp. 548-549 Read, only a. winds circulate and towards the b. air tends to be warm, moist, and cloudy c. air rises in the centers of cyclones - warm, moist air has a low density d. these can form at a Polar Front - where cold air from higher latitudes meets warmer air from lower latitudes - mid-latitudes like NYS Topic 12 pp. 531-532 TQ p. 534 12e only 2. Anticyclone - High Pressure Center - Divergent Air Mass a. winds circulate and b. air tends to be cold, dry, and clear c. air sinks in the centers of anticyclones - cold, dry air has a high density Page 8 of 11
K. Source Regions - those areas on the Earth s surface where air masses form and acquire their characteristics - there are 5 source regions that produce air masses that influence weather in NYS 1. Arctic Continental - ca - and - anticyclones - limited to winter in NYS - form up near the North Pole 2. Polar Continental - cp - and - anticyclones - form in central Canada and move into NYS 3. Polar Maritime - mp - and - form over the North Atlantic Ocean 4. Tropical Continental - ct - and - form over the SW United States and Mexico 5. Tropical Maritime - mt - and - cyclones - form over warm oceans like the Gulf of Mexico Topics 6&7 pp. 561-562 TQ s p. 564 6ab, 7ac not b a. they can develop into hurricanes b. hurricanes get their energy from the condensation of water vapor c. they die out over land having lost their source of moisture d. they follow a path called a track - can impact weather in NYS Shortcut : A=extremely cold, P=cold, T=warm, m=moist, c=dry Facts about source regions/air masses a. an air mass must stagnate (stop moving) over a source region to acquire the characteristics of that source region b. in the United States, air masses track from southwest to northeast under the influence of the prevailing winds and the jet stream c. polar and arctic air is from higher latitudes while tropical air is from lower latitudes L. Fronts - the boundary or interface between 2 different - where 2 or more air masses meet Topics 6&7 pp. 547-548 TQ s p. 549 6abc, 7ab Page 9 of 11
NOTE : whenever warm air and cold air meet, the warm air is forced to rise over the frontal interface There are 4 basic types of fronts: 1. Cold Front - an anticyclone overtaking a cyclone - they call it a cold front because it s the front of the advancing cold air Topic 11 p. 551 TQ p. 551 11ab Topics 1&2 pp. 557-558 TQ s p. 560 1ab, 2ab a. as the front passes over you: 1) short, precipitation from cumulonimbus clouds 2) air temperatures - it IS a cold front 3) winds shift to the north from the south b. after the front passes over you: 1) skies clear 2) the air pressure 3) relative humidity NOTE : on a weather map, the precipitation is occurring right along the frontal line 2. Warm Front - a cyclone overrunning an anticyclone - they call it a warm front because it s the front of the advancing warm air Topic 10 p. 550 TQ p. 551 10ab a. as the front passes over you: 1) slow, steady precipitation from stratus or nimbostratus clouds 2) air temperatures - it IS a warm front 3) winds shift to the south from the north b. after the front passes over you: 1) skies remain 2) the air pressure continues to 3) relative humidity remains NOTE : on a weather map, the precipitation precedes the frontal line itself 3. Occluded Front - warm air is trapped above/between 2 cooler air masses Page 10 of 11
a. it s associated with lots of precipitation where the air masses meet 4. Stationary Front - 2 different air masses are in contact, but neither is moving a. the air masses are said to stall b. steady precipitation right at the frontal line Page 11 of 11