1. Prof. John Toohey-Morales, CCM
Temperature
Prof. John Toohey-Morales, CCM
St. Thomas University
Miami Gardens, Florida

2. Daytime Warming Sun’s radiant energy heats the ground
Ground warms the air by conduction
Air rises (thermals) to warm the air above by convection
Calm days: Thermals are small so the air at the surface is much hotter
Windy days: Mechanical stirring causes forced convection and warm air is mixed upwards

3. Daytime Warming (continued)

4. Lag in Temperature
Noon is when the Sun’s rays are the most intense, but NOT the peak of outgoing IR
Earth continues to absorb solar radiation past noon
Maximum temperature occurs as outgoing IR energy and incoming solar energy balance

5. Hottest Places
Deserts because of sand, low humidity, clear sky and lack of vegetation
136°F (58°C) El Azizia, Libya
134°F (57°C) Death Valley, California
Phoenix, AZ average July hi temp is 105°F
Atlanta, GA is at the same latitude as Phoenix but July average hi temp is 87°F
Humidity, haze, clouds make days cooler

6. Nighttime Cooling
During radiational cooling ground cools faster than air
Air in contact with ground gets colder before the air above: nocturnal inversion
Ideal 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 evaporates
Dense, cold air drains into valleys, making them colder than surroundings
Record cold temperatures
Minus 129°F (-89°C) in Vostok, Antarctica
Minus 80°F (-62°C) in Prospect Creek AK

8. Protecting Agriculture
Crops can be severely damaged by cold
Wind Machines are fans used to mix cold ground air with warmer air above
Sprinklers 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 Controls
Latitude (sunshine), land & water distribution (specific heat), ocean currents, elevation

10. Temperature Data
Diurnal Range: Difference between maximum & minimum daily temperature
HIGH: deserts
LOW: humid regions, water, urban heat island
Mean Daily Temperature: Average of the high and low temp for a 24-hour period
“Normal” temperature is a 30-year average
Annual Range: Difference between average temperature of the warmest and coldest months
HIGH: mid-high latitudes LOW: near the equator

11. A Tale of Two Cities
Mean Annual Temp: Average of the 12 monthly mean temps
San 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 environment
Body 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 air
In 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 air
WCI: 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 air
Hot, 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