1/2/2016 WEATHER DEFINITION

Transcription

1 WEATHER DEFINITION Weather state or condition of the variables of the atmosphere at a given time Weather variables temperature, air pressure, wind, moisture, cloud cover, precipitation, storms Weather occurs in the troposphere (lower layer of the atmosphere) Heat energy (insolation) is what drives weather WEATHER Most weather occurs in troposphere. Due to our tilt, variations in insolation cause heat energy to be unevenly distributed The movement of heat energy results in changes in the atmosphere that are the cause of WEATHER In NY State, most of our weather comes from the West/Southwest. Weather Movement From West/SW Towards Northeast TEMPERATURE REVIEW Reminder: use page 13 on ref. table to convert temperatures Three Scales: Fahrenheit, Celsius, Kelvin Isotherms lines that connect equal lines of temperature ISOTHERMS 1

2 HEATING THE ATMOSPHERE More insolation = higher temperatures Conduction moves heat Earth s surface to the atmosphere Absorption of insolation by gases and aerosols Absorption of infrared radiation given off by Earth s surface Condensation and (sublimation) gives off stored heat when clouds form Coriolis Effect due to rotation and winds friction between air and Earth s surface ANOTHER IMPORTANT HEAT TRANSFER Convection due to differences in density Convection Currents air moving in circular patterns EXPANSION AND COMPRESSION When a gas expands, its temperature decreases (molecules further apart) When a gas compresses, its temperature increases (molecules collide) Warm air rises- expands and then cools Cool air sinks- compresses and then warms PRESSURE WEIGHT OF AIR DIFFERENCES IN AIR PRESSURE ARE CAUSED PRIMARILY BY UNEQUAL HEATING OF EARTH S SURFACE Measured by a barometer Increase density, increase pressure Increase temperature, decrease pressure and density Increase altitude, decrease pressure Increase water vapor content, decrease pressure Isobars = lines of equal pressure (MEMORIZE THESE!!!) Increase temperature decrease pressure Mercury Barometer PRESSURE Temp. 2

3 Pressure and Density Decrease with ALTITUDE ISOBARS ARE ISOLINES OF EQUAL PRESSURE Where is the pressure gradient the steepest on this map? EFFECTS OF WEATHER VARIABLES ON PRESSURE Higher air temperature = lower density air = lower air pressure ( T = D = P ) More water vapor in the air = lower pressure (H 2 O weighs less than air nitrogen and oxygen) Higher altitude = lower pressure (remember air rises, expands, and then cools) 3

4 ATMOSPHERIC MOISTURE Exists in solid, liquid, and gas in atmosphere Water enters the atmosphere by: Evaporation liquid changes into gas Transpiration plants release water vapor Evapotranspiration evaporation + transpiration together Remember, it s the Sun that provides the energy for these to occur FACTORS AFFECTING EVAPORATION: amount of energy available (more energy = faster evaporation) surface area of the water (spread out/more s.a. = faster evaporation) degree of saturation (more saturated = slower evaporation) wind speed (greater wind speed = greater evaporation) HUMIDITY RELATIVE HUMIDITY Absolute Humidity - water vapor in each unit volume of air (or moisture capacity) - hotter air can hold more water vapor than cold air Relative humidity ratio of the amount of water vapor in the air to maximum amount it can hold The one you see in forecasts RELATIVE HUMIDITY If you had 20oz of water, which bottle would be full? The full, 20oz bottle would be at 100% relative humidity. If the same 20oz filled the 1 gal. (128oz) bottle, it would only fill about 16% of it. That would be 16% relative humidity. Or 5% of the 3 gallon. (128oz) RELATIVE HUMIDITY GIVEN IN % Does not tell you the amount of water vapor in the air DOES TELL YOU HOW CLOSE IT IS TO BEING SATURATED SATURATION filled to capacity with water vapor the RH is 100% Relative Humidity DECREASES as Temperature INCREASES 4

5 WHICH IS HEAVIER? Which is heavier: dry air or wet air? Would a baseball travel further on a night where the air is saturated or dry? (ignoring wind speed) When water vapor replaces other air molecules (oxygen, nitrogen) that are heavier, the humid air actually weighs LESS! Therefore, a baseball can travel further on a night when the air is saturated. DEW POINT Dew point temperature at which air is saturated (filled with water) If air temp = dew point, relative humidity = 100% If air temp drops below dew point: water vapor condenses to liquid water If air temp = dew point, relative humidity = 100% DEW POINT TEMPERATURE The temperature that the air is saturated (filled with water vapor) Relative Humidity is 100% Air Temperature = Dew Point Temperature, CONDENSATION begins Dew Point Temperature is a measure of how much water vapor in the air Dew Point Temperature will rise as water vapor content of the air increases 5

6 MEASURING MOISTURE Sling Psychrometer instrument used to measure relative humidity and dew point Dry bulb temp ordinary thermometer (aka: air temp.) Wet bulb temp thermometer with wet wick around it DPT & RELATIVE HUMIDITY CHARTS Earth Science Reference Tables Page 12 THE DRY BULB Don t let it fool you. It is just a thermometer. It measures the air temperature. 20 C THE WET BULB A DRY DAY Has a little wet booty tied to the bottom. Gets cool when water evaporates. 12 C A lot of moisture will evaporate. The wet bulb will be a lot cooler than the dry bulb. 20 C 8 C 20-8=12; Difference between wet bulb & dry bulb is 12 C. Wet Booty 6

7 A HUMID DAY A little bit of moisture will evaporate. The wet bulb will not be much cooler than the dry bulb. 20 C 20-14= 6 Difference between wet bulb & dry bulb is 6 C. 14 C PAGE 12 OF YOUR EARTH SCIENCE REFERENCE TABLES Warning #1: Be sure to READ the correct chart: DPT or RH Warning #2: Dew Point Temperature IS NOT Difference between wet bulb and dry bulb. Warning #3: The wet bulb temp IS NOT the DPT. TO CONVERT RELATIVE HUMIDITY AND DEW POINT Dry-bulb temperature is your air temperature. 20 C You must use page 12 of ref. table 1. Subtract: dry bulb temp wet bulb 2. Locate dry bulb on left side 3. Locate answer to step 1 on top of chart 4. See where those two numbers meet ****Make sure you are using the correct chart: dew point or relative humidity**** Subtract (the difference) between the dry bulb and wet bulb Put it all together Wet bulb = 8 C 20 C 8 C 20-8=12 Relative Humidity = 11% 7

8 INGREDIENTS FOR CLOUD FORMATION 1. Evaporation and Transpiration (puts water vapor in air) 2. Air rises and cools due to expansion 3. Cools to dew point temperature 4. Condensation begins on condensation surface (aerosols dust, salt crystals) 5. Cloud forms 6. Precipitation occurs if cloud droplets get too big RISING AIR EXPANDS & COOLS 8

9 Which graph best represents the relationship between water droplet size and precipitation? 9

10 CONVECTION DUE TO UNEQUAL HEATING 1. Evaporation 2. Rising and Cooling to dew point temperature 3. Condensation begins on condensation surface (aerosols, dust) 4. Cloud forms 5. Drops get big enough precipitation begins WINDWARD / LEEWARD Humid air is forced to rise over mountains. Air rises, cools & condenses on the windward side and is warm & dry on the leeward side (rain shadow). Called the orographic effect. YOU MUST KNOW THIS! 10

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