MADISON’S CURRENT WEATHER Madison Weather at 1000 AM CDT 10 JUL 2002 Updated twice an hour at :05 and :25 Sky/Weather: CLOUDY Temperature: 70 F (21 C) Dew Point: 62 F (16 C) Relative Humidity: 76% Wind: E10 MPH Barometer: 30.20R (1022.7 mb) http://www.ssec.wisc.edu/localweather/

                                                                                                                                                                                                                                                                                                                                          Last 24 hrs in Madison http://weather.uwyo.edu/cities/

http://www.ssec.wisc.edu/data/east/latest_eastvis.jpg CURRENT VISIBLE

http://www.ssec.wisc.edu/data/east/latest_eastir.jpg CURRENT IR

http://www.ssec.wisc.edu/data/east/latest_eastwv.jpg CURRENT WATER VAPOR

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

Current Surface Winds with Streamlines & Isotachs (“iso” = equal & “tach” = speed) http://image.weather.com/images/maps/boat-n-beach/us_wind_cur_720x486.jpg H

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

Current Temperatures (oF) – 24 Hrs Ago Cold Advection + Drier Air http://maps.weather.com/images/maps/special/24h_temp_chg_720x486.jpg

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

Current Apparent Temperatures (oF) http://maps.weather.com/images/maps/current/actheat_720x486.jpg

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

Announcements Please pick up Exams and homeworks! If you have ??, please see me.

ATM OCN 100 - Summer 2002 LECTURE 10 (con’t.) WATER & THE HYDROLOGIC CYCLE Introduction Importance of the Hydrologic Cycle Assessing the Hydrologic Cycle Water: A Wonder

C. ASSESSING THE HYDROLOGIC CYCLE Mass Budgets Total Water Budget of Planet Earth Measurement Techniques Precipitation = Evaporation + Storage (change in water level)

“Rain Sensor” for NWS Automatic Weather Station

Evaporation Pan From J.M. Moran & WES Project of AMS http://www.ametsoc.org/amsedu/WES/WESSlides/WESThumbnailHyperlinks/ch10/s041evaporation_pan.htm

Evapotranspiration Combination of: Transpiration Evaporation

D. WATER - A WONDER Background Molecular Structure of Water (H2O) A “dipole”

Molecular Structure of H2O Chemical Properties of H2O D. WATER - A WONDER Molecular Structure of H2O Chemical Properties of H2O Physical Properties of H2O

D. WATER - A WONDER (con’t) Physical Properties of H2O Three Phases & High Latent heats High Specific heat Anomalous Density & temperature relationship Heat conductivity An excellent absorber/emitter of IR radiation where...

PHYSICAL PHASES of H2O Solid (Ice) – “Low Energy” -- Note Hexagonal (6 sided) Structure

PHYSICAL PHASES of H2O Liquid “Medium Energy”

PHYSICAL PHASES of H2O Vapor “High Energy”

Physical Phase Changes of H2O See Fig 4.2 Moran & Morgan (1997)

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

Implications Large amounts of latent heat are utilized to transfer surplus energy from earth’s surface to the atmosphere. Maritime vs. Continental Climate

At Southern Lake Michigan Buoy

                                                                                                                                                                                                                                                                                                                                          Last 24 hrs in Madison http://weather.uwyo.edu/cities/

SPECIFIC HEAT Recall Sensible Heat Specific Heat Quantity of heat required to change temperature of a unit mass of substance by 1 Celsius degree.

SPECIFIC HEATS Water has a high specific heat [Table 3. 2, pg SPECIFIC HEATS Water has a high specific heat [Table 3.2, pg. 76 Moran & Morgan, 1997]

TEMPERATURE RESPONSE for substances with differing specific heats See Table 3.2, Moran & Morgan (1997)

Implications For the same amount of heat energy added, Water takes longer to heat. Maritime vs. Continental Climate

DENSITY OF LIQUID WATER

Implications Ice expands when water freezes; Ice floats; Lakes freeze from top down.

Freezing cycle of lakes

Madison skyline from frozen Lake Monona

HEAT CONDUCTIVITY [Table 3.1, pg. 74 Moran & Morgan, 1997]

Implications Water is efficient at conducting heat. Humans can suffer hypothermia when immersed in cold water: Survival time in 32.5° F water is 15 to 45 minutes!

IR Absorption/Emission Properties of H2O Water molecules are great absorbers (& emitters) of IR radiation Consequences Water vapor is the most dominant “Greenhouse Gas” Clouds (liquid & ice) elevate nighttime temperatures Snow surfaces are great emitters

Humidity (Atmospheric vapor) Considerations E. WATER VAPOR Properties A colorless gas Found in many locations Humidity (Atmospheric vapor) Considerations

E. WATER VAPOR Concept of Saturation A dynamic equilibrium between Evaporation & Condensation; Depends upon temperature of system.

E. WATER VAPOR (con’t.) SPECIFICATION OF WATER VAPOR @ SATURATION Consider Saturation vapor pressure. Recall concept of Dalton’s Law of Partial Pressure: PTotal = p(N2) + p(O2) + p(Ar) + e + … where e = (partial water) vapor pressure. Now consider values of e at saturation conditions, defined as es(T)

SATURATION VAPOR PRESSURE as FUNCTION OF TEMPERATURE Fig. 6. 3, pg SATURATION VAPOR PRESSURE as FUNCTION OF TEMPERATURE Fig. 6.3, pg. 133 - Moran & Morgan, 1997

E. WATER VAPOR (con’t.) What is Boiling? Boiling point depends on air pressure; Variation of boiling point with altitude; Pressure cookers Vacuum evaporators

SATURATION VAPOR PRESSURE as FUNCTION OF TEMPERATURE Fig. 6. 3, pg SATURATION VAPOR PRESSURE as FUNCTION OF TEMPERATURE Fig. 6.3, pg. 133 - Moran & Morgan, 1997 Sea Level: Tbp = 100°C = 212°F 5000 ft: Tbp = 95°C = 203°F 10,000 ft: Tbp = 90°C = 194°F From p6 Reifsnyder (1980) See bp-z.xls

E. WATER VAPOR (con’t.) Humidity Measurement & Instruments hair hygrometer dewpoint hygrometer sling psychrometer hygristor where...

HUMIDITY INSTRUMENTS HAIR HYGROMETER Measure how length of hair varies with relative humidity changes.

HUMIDITY INSTRUMENTS (con’t.) DEWPOINT HYGROMETER Cool surface and measure temperature at which water vapor condenses (i.e., forms dew).

Hygrometer & Thermal Sensor at ASOS

HUMIDITY INSTRUMENTS (con’t.) SLING PSYCHROMETER Measure temperature when evaporation causes cooling of a moist surface by ventilation to point where no additional evaporation takes place.

Sling Psychrometer (con’t.)

Sling Psychrometer (con’t.)

Inside an Instrument Shelter

HUMIDITY INSTRUMENTS (con’t.) HYGRISTOR Measure electrical resistance of a substance which varies with relative humidity.

Hygristor on a Radiosonde

WATER VAPOR (con’t.) Water Vapor Variables vapor pressure mixing ratio dewpoint (& frostpoint) wet-bulb temperature relative humidity apparent temperature/heat index defined as....

WATER VAPOR (con’t.) (Water) Vapor Pressure Partial pressure exerted by water vapor molecules; Range: 0 mb to 40 mb under normal conditions; Determined indirectly.

WATER VAPOR (con’t.) Dewpoint temperature Temperature to which air is cooled at constant pressure & without change in vapor content to reach saturation; Obtained from dewpoint hygrometer; Typically less than air temperature, except for saturation or supersaturation; When Tdew > 65oF, human discomfort increases.

WATER VAPOR (con’t.) Frostpoint temperature Saturation point at temperatures below freezing point (T < 0oC) when “frost” could be formed. Frost forms directly through deposition.

WATER VAPOR (con’t.) Wet-bulb temperature Temperature resulting when air is cooled to saturation by evaporation of water; Cooling produced by latent heat of evaporation; Measured by a sling psychrometer; Lower atmospheric vapor content produces lower Twet-bulb.

WATER VAPOR (con’t.) Wet-bulb temperature Used to obtained other moisture variables such as dewpoint & relative humidity; Requires dry bulb, wet-bulb readings & determination of wet-bulb depression; Read Tdew or RH from psychometric tables.

Psychrometric Tables Table A: Relative Humidity [%] Inside cover, Moran and Morgan (1997)

Psychrometric Tables Table B: Dewpoint Temperature (C) Inside cover, Moran and Morgan (1997)

WATER VAPOR (con’t.) Water Vapor Variables vapor pressure mixing ratio dewpoint (& frostpoint) wet-bulb temperature relative humidity apparent temperature/heat index defined as....

WATER VAPOR (con’t.) Relative Humidity A measure of the relative closeness to saturation conditions; Requires specification of air temperature; RH = 100% at saturation (i.e., dewpoint).

SATURATION VAPOR PRESSURE as FUNCTION OF TEMPERATURE Fig. 6. 3, pg SATURATION VAPOR PRESSURE as FUNCTION OF TEMPERATURE Fig. 6.3, pg. 133 - Moran & Morgan, 1997

WATER VAPOR (con’t.)

WATER VAPOR (con’t.)

Diurnal Variation in Relative Humidity See Fig. 6 Diurnal Variation in Relative Humidity See Fig. 6.5 Moran & Morgan (1997) NOTE: Dewpoint ranged between 8° to 9° C during day

WATER VAPOR (con’t.) Apparent Temperature/Heat Index An index based upon heat loss from human body; Incorporates role of evaporative cooling by perspiration (sweating); Used for high temperatures & high relative humidities; Human comfort/safety: Heat Stress.

Apparent Temperature (°F) – Heat Index From NWS

Late Sunday Afternoon Temperatures (oF) http://maps.weather.com/images/maps/current/acttemp_720x486.jpg

Late Sunday Afternoon Dewpoints (oF) http://maps.weather.com/images/maps/current/actdew_720x486.jpg

Late Sunday Afternoon Apparent Temperatures/Heat Indices (oF) http://maps.weather.com/images/maps/current/actheat_720x486.jpg

Announcements Homework #3 is returned today Answer Key is posted at http://www.aos.wisc.edu/~hopkins/aos100/homework Homework #4 is due Thurs. 2nd Hour Exam is scheduled for Thurs. Study sheet is posted at: http://www.aos.wisc.edu/~hopkins/aos100/exams If you have ??, please see me.

WATER VAPOR (con’t.) Climatology of Atmospheric Humidity tropical vs. polar maritime vs. continental

Rule of thumb When: Air temperature falls to within 2 to 3 Fahrenheit degrees of dewpoint and Winds are light Then: Fog often forms.