ATM OCN 100 – Summer 2002 LECTURE 6 (con’t.) ATMOSPHERIC ENERGETICS: HEAT, ENERGY & ENERGY TRANSPORT A. Introduction B. Energy & Power Definitions Energy in atmosphere C. Energy Exchange Processes D. Heat Energy E. Practical Example – Wind-Chill

MADISON’S CURRENT WEATHER Madison Weather at 1000 AM CDT WED 26 JUN 2002 Updated twice an hour at :05 and :25 Temperature: 68F ( 20C) Dewpoint: 63F ( 17C) Relative Humidity: 84% Winds from the W (270 degs) at 6 mph. Pressure: 1012.1 millibars. Altimeter:29.90 inches of mercury. http://www.ssec.wisc.edu/localweather/

Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts and Radar http://maps.weather.com/images/maps/current/curwx_720x486.jpg

Current Temperatures (°F) & Isotherms (“iso” = equal +”therm” = temperature) http://maps.weather.com/images/maps/current/acttemp_720x486.jpg

Current Dewpoints (oF) http://maps.weather.com/images/maps/current/actdew_720x486.jpg

Tomorrow AM Forecast Map http://maps.weather.com/images/maps/forecast/amfcst_720x486.jpg

This morning’s low temperatures (oF) http://maps.weather.com/images/maps/current/actual_los_720x486.jpg

Yesterday’s high temperatures (oF) http://maps.weather.com/images/maps/current/curtemps_720x486.jpg

Yesterday’s High Temperatures (oF) – (1961-90) Average High Temperatures http://maps.weather.com/images/maps/special/norm_dep_hi_720x486.jpg

This morning’s low temperatures (oF)

Yesterday’s high temperatures (oF)

Yesterday’s High Temperatures (oF) – (1961-90) Average High Temperatures

ATM OCN 100 - Summer 2002 LECTURE 6 ATMOSPHERIC ENERGETICS: HEAT, ENERGY & ENERGY TRANSPORT A. INTRODUCTION What maintains the operation of our planetary system?

B. ENERGY & POWER Definitions Energy: Ability of a system to do work. Power: Time rate of energy production or consumption. Importance

B. ENERGY & POWER (con’t.) Types of Energy (In the Atmosphere) Kinetic Potential Radiant Internal or “heat” energy Chemical Physical phase Transformation Electrical

B. ENERGY & POWER (con’t.) Energy Units British Thermal Units (BTU) Calories Joules Power Units Watts

C. ENERGY EXCHANGE PROCESSES (Specification by Thermodynamics Laws) Conservation of energy (1st Law) Energy cannot be created or destroyed; Energy can change forms; Energy can be transported. Energy transport Requirements (2nd Law) From high energy (hot) to low energy (cold).

C. ENERGY EXCHANGE PROCESSES (con’t.) Types of energy exchange or transport modes Conduction Convection Radiation where...

ENERGY TRANSPORT: CONDUCTION Energy transfer by molecular vibrational motion. Requires molecular contact: Transport medium is typically a solid. In general: Metals are good heat energy conductors; Air is a poor heat conductor.

Thermal Conductivity Example: Change in Snow Cover See Figure 3 Thermal Conductivity Example: Change in Snow Cover See Figure 3.6, Moran & Morgan (1997) Old snow and Ice Fresh snow

ENERGY TRANSPORT: CONVECTION Energy Transport by molecular motion through bulk transport. Requires movement of medium: Transport medium is a fluid only. In general: Fluid density differences drive convection; Convection works well in air & water.

ENERGY TRANSPORT: CONVECTION (con’t.)

ENERGY TRANSPORT: RADIATION Energy Transport is by radiating disturbances in electrical & magnetic fields. Does not requires a medium: Transport most efficient in vacuum. Radiation is important for maintenance of planetary climate.

D. HEAT (or HEAT ENERGY) Definition A form of energy; Proportional to total amount of thermal energy found in object. Important considerations Heat Flow Requires a temperature difference; Flow from hot to cold.

Adding heat to a substance can… Increase the temperature (by increasing internal energy) Cause a phase change of H2O (melting or evaporating) Change the volume of the gas

D. HEAT ENERGY (con’t.) Sensible heat “Feelable Heat” Measurement of heat & thermal energy: Change in heat = constant x temperature change Where constant = specific heat of a substance; If 1 calorie is heat needed to raise 1 gm of H20 by 1 Celsius degree, then Specific heat of H2O = 1 cal per gram.

D. HEAT ENERGY (con’t.) Latent heat “Hidden Heat” Involves Physical Phase Transformation of H2O ; No temperature change.

Distinguishing Sensible & Latent Heats See Fig 4 Distinguishing Sensible & Latent Heats See Fig 4.3 Moran & Morgan (1997)

E. A PRACTICAL EXAMPLE WIND-CHILL & WIND-CHILL EQUIVALENT TEMPERATURE What do these terms mean? Human significance.

WIND-CHILL & WIND CHILL EQUIV. TEMP. BACKGROUND HEAT LOSS FROM HUMANS Radiation; Convective Heat Loss; Latent Heat Loss. CONVECTIVE HEAT LOSS depends upon: Difference between skin & air temperature; Wind speed.

THE DEFINITIONS (con’t.) WIND-CHILL EQUIVALENT TEMPERATURE (WET) A temperature-based index Units degrees Fahrenheit (or Celsius). Air temperature for calm conditions that produces same convective heat loss as actual combination of ambient air temperature & wind speed; So, if Air T = 30°F & wind speed = 20 mph, then using Table 3.3B (Moran & Morgan), WET = 4°F when we assume calm conditions (since heat loss is same for both actual case & calm conditions)!!

Wind Chill Equivalent Temperatures See also Tables 3. 3A& 3 Wind Chill Equivalent Temperatures See also Tables 3.3A& 3.3B Moran & Morgan (1997)

New NWS Wind Chill Equivalent Temperatures Compare with Tables 3.3A& 3.3B Moran & Morgan (1997) http://www.crh.noaa.gov/mkx/winter_page.htm

Current Temperatures (oF) & Isotherms

Current Wind-Chill Equivalent Temperatures (oF)