Presentation on theme: "Prof. John Toohey-Morales, CCM"— Presentation transcript:
1 Prof. John Toohey-Morales, CCM TemperatureProf. John Toohey-Morales, CCMSt. Thomas UniversityMiami Gardens, Florida
2 Daytime Warming Sun’s radiant energy heats the ground Ground warms the air by conductionAir rises (thermals) to warm the air above by convectionCalm days: Thermals are small so the air at the surface is much hotterWindy days: Mechanical stirring causes forced convection and warm air is mixed upwards
4 Lag in TemperatureNoon is when the Sun’s rays are the most intense, but NOT the peak of outgoing IREarth continues to absorb solar radiation past noonMaximum temperature occurs as outgoing IR energy and incoming solar energy balance
5 Hottest PlacesDeserts because of sand, low humidity, clear sky and lack of vegetation136°F (58°C) El Azizia, Libya134°F (57°C) Death Valley, CaliforniaPhoenix, AZ average July hi temp is 105°FAtlanta, GA is at the same latitude as Phoenix but July average hi temp is 87°FHumidity, haze, clouds make days cooler
6 Nighttime CoolingDuring radiational cooling ground cools faster than airAir in contact with ground gets colder before the air above: nocturnal inversionIdeal conditions include long, clear nights, calm winds and dry air
7 Coolest Time and Places IR radiation continues as sun rises and air may still cool further as sunlight is too dim / dew evaporatesDense, cold air drains into valleys, making them colder than surroundingsRecord cold temperaturesMinus 129°F (-89°C) in Vostok, AntarcticaMinus 80°F (-62°C) in Prospect Creek AK
8 Protecting Agriculture Crops can be severely damaged by coldWind Machines are fans used to mix cold ground air with warmer air aboveSprinklers can coat buds & fruit with water that can turn to ice. The latent heat from freezing keeps the ice temperature at 32°F, protecting the fruit at a higher temperature than the subfreezing air.
9 Temperature ControlsLatitude (sunshine), land & water distribution (specific heat), ocean currents, elevation
10 Temperature DataDiurnal Range: Difference between maximum & minimum daily temperatureHIGH: desertsLOW: humid regions, water, urban heat islandMean Daily Temperature: Average of the high and low temp for a 24-hour period“Normal” temperature is a 30-year averageAnnual Range: Difference between average temperature of the warmest and coldest monthsHIGH: mid-high latitudes LOW: near the equator
11 A Tale of Two CitiesMean Annual Temp: Average of the 12 monthly mean tempsSan Francisco, CA & Richmond, VA have the same mean annual temperature (57°F), but at 21°F Richmond’s average January low is much lower than the coldest ever recorded in San Francisco
12 Sensible Temperature Defined as the temperature we perceive Constant exchange of heat between the body’s skin and the environmentBody radiates, conducts and initiates convection so that a thin layer of warm air molecules forms close to the skin, protecting it from the surrounding cold airIn calm air, a cold day feels “warmer”
13 Wind Chill Index (WCI)When the wind blows, the insulating layer of air near the skin is swept away & heat is rapidly removed by cold airWCI: How cold the wind makes us feel
14 Moisture and The Way We Feel Cold, rainy, drizzly, foggy days feel colder than “dry” days because water on the skin conducts heat away better than airHot, humid days feel hotter than hot / dry days because perspiration can’t be readily evaporated due to near-saturation of the surrounding air (less evaporational cooling)
15 Measuring Temperature It is impossible to measure air temperature accurately in direct sunlight because the thermometer absorbs radiant energy from the sun in addition to energy from the air molecules (needs shelter)Liquid-in-glass (mercury or alcohol) & electrical thermometers are calibrated to insure uniform readings
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