MADISONS CURRENT WEATHER Madison Weather at 1000 AM

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: E 10 MPH Barometer: 30. 20 R (1022. 7 mb)

Last 24 hrs in Madison ATM OCN 100 Summer 2002 7

ATM OCN 100 Summer 2002 CURRENT VISIBLE 8

CURRENT IR ATM OCN 100 Summer 2002 9

CURRENT WATER VAPOR ATM OCN 100 Summer 2002 10

Current Surface Weather Map with Isobars (“iso” = equal & “bar” = weight), Fronts and Radar ATM OCN 100 Summer 2002 11

Current Surface Winds with Streamlines & Isotachs (“iso” = equal & “tach” = speed) H L LL ATM OCN 100 Summer 2002 L H H H L L 12

Current Temperatures (°F) & Isotherms (“iso” = equal +”therm” = temperature) ATM OCN 100 Summer 2002 14

Current Temperatures (o. F) – 24 Hrs Ago Cold Advection + Drier Air ATM OCN 100 Summer 2002 15

Current Dewpoints (o. F) ATM OCN 100 Summer 2002 16

Current Apparent Temperatures (o. F) ATM OCN 100 Summer 2002 17

Tomorrow AM Forecast Map ATM OCN 100 Summer 2002 18

Announcements u Please pick up Exams and homeworks! u If you have ? ? , please see me. ATM OCN 100 Summer 2002 45

ATM OCN 100 - Summer 2002 LECTURE 10 (con’t. ) WATER & THE HYDROLOGIC CYCLE A. B. C. D. Introduction Importance of the Hydrologic Cycle Assessing the Hydrologic Cycle Water: A Wonder ATM OCN 100 Summer 2002 73

C. ASSESSING THE HYDROLOGIC CYCLE u Mass Budgets u Total Water Budget of Planet Earth u Measurement Techniques Precipitation = Evaporation + Storage (change in water level) ATM OCN 100 Summer 2002 74

“Rain Sensor” for NWS Automatic Weather Station ATM OCN 100 Summer 2002 75

Evaporation Pan From J. M. Moran & WES Project of AMS ATM OCN 100 Summer 2002 76

Evapotranspiration u Combination of: – Transpiration – Evaporation ATM OCN 100 Summer 2002 77

D. WATER - A WONDER u Background – Molecular Structure of Water (H 2 O) A “dipole” ATM OCN 100 Summer 2002 78

D. WATER - A WONDER u. Molecular Structure of H 2 O u. Chemical Properties of H 2 O u. Physical Properties of H 2 O ATM OCN 100 Summer 2002 81

D. WATER - A WONDER (con’t) u Physical – – – Properties of H 2 O Three Phases & High Latent heats High Specific heat Anomalous Density & temperature relationship Heat conductivity An excellent absorber/emitter of IR radiation where. . . ATM OCN 100 Summer 2002 82

PHYSICAL PHASES of H 2 O u. Solid (Ice) – “Low Energy” -- Note Hexagonal (6 sided) Structure ATM OCN 100 Summer 2002 83

PHYSICAL PHASES of H 2 O u. Liquid “Medium Energy” ATM OCN 100 Summer 2002 84

PHYSICAL PHASES of H 2 O u. Vapor “High Energy” ATM OCN 100 Summer 2002 85

Physical Phase Changes of H 2 O See Fig 4. 2 Moran & Morgan (1997) ATM OCN 100 Summer 2002 87

Distinguishing Sensible & Latent Heats See Fig 4. 3 Moran & Morgan (1997) ATM OCN 100 Summer 2002 88

Implications u Large amounts of latent heat are utilized to transfer surplus energy from earth’s surface to the atmosphere. u Maritime vs. Continental Climate ATM OCN 100 Summer 2002 90

ATM OCN 100 Summer 2002 91

At Southern Lake Michigan Buoy ATM OCN 100 Summer 2002 92

Last 24 hrs in Madison ATM OCN 100 Summer 2002 93

SPECIFIC HEAT u Recall – Sensible Heat Specific Heat Quantity of heat required to change temperature of a unit mass of substance by 1 Celsius degree. ATM OCN 100 Summer 2002 94

SPECIFIC HEATS Water has a high specific heat [Table 3. 2, pg. 76 Moran & Morgan, 1997] ATM OCN 100 Summer 2002 95

TEMPERATURE RESPONSE for substances with differing specific heats See Table 3. 2, Moran & Morgan (1997) ATM OCN 100 Summer 2002 96

Implications u For the same amount of heat energy added, Water takes longer to heat. u Maritime vs. Continental Climate ATM OCN 100 Summer 2002 97

DENSITY OF LIQUID WATER ATM OCN 100 Summer 2002 98

Implications u Ice expands when water freezes; u Ice floats; u Lakes freeze from top down. ATM OCN 100 Summer 2002 99

Freezing cycle of lakes ATM OCN 100 Summer 2002 100

Madison skyline from frozen Lake Monona ATM OCN 100 Summer 2002 101

HEAT CONDUCTIVITY [Table 3. 1, pg. 74 Moran & Morgan, 1997] ATM OCN 100 Summer 2002 102

Implications u Water is efficient at conducting heat. u Humans can suffer hypothermia when immersed in cold water: – Survival time in 32. 5° F water is 15 to 45 minutes! ATM OCN 100 Summer 2002 103

IR Absorption/Emission Properties of H 2 O u Water molecules are great absorbers (& emitters) of IR radiation u Consequences – Water vapor is the most dominant “Greenhouse Gas” – Clouds (liquid & ice) elevate nighttime temperatures – Snow surfaces are great emitters ATM OCN 100 Summer 2002 104

E. WATER VAPOR u Properties – A colorless gas – Found in many locations u Humidity (Atmospheric vapor) Considerations ATM OCN 100 Summer 2002 105

E. WATER VAPOR u Concept of Saturation – A dynamic equilibrium between Evaporation & Condensation; – Depends upon temperature of system. ATM OCN 100 Summer 2002 106

E. WATER VAPOR (con’t. ) SPECIFICATION OF WATER VAPOR @ SATURATION u Consider u Recall Saturation vapor pressure. concept of Dalton’s Law of Partial Pressure: PTotal = p(N 2) + p(O 2) + p(Ar) + e + … where e = (partial water) vapor pressure. u Now consider values of e at saturation conditions, defined as es(T) ATM OCN 100 Summer 2002 107

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

E. WATER VAPOR (con’t. ) u What is Boiling? – Boiling point depends on air pressure; – Variation of boiling point with altitude; – Pressure cookers – Vacuum evaporators ATM OCN 100 Summer 2002 109

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

E. WATER VAPOR (con’t. ) u Humidity Measurement & Instruments – hair hygrometer – dewpoint hygrometer – sling psychrometer – hygristor where. . . ATM OCN 100 Summer 2002 111

HUMIDITY INSTRUMENTS u HAIR HYGROMETER – Measure how length of hair varies with relative humidity changes. ATM OCN 100 Summer 2002 112

HUMIDITY INSTRUMENTS (con’t. ) u DEWPOINT HYGROMETER – Cool surface and measure temperature at which water vapor condenses (i. e. , forms dew). ATM OCN 100 Summer 2002 113

Hygrometer & Thermal Sensor at ASOS ATM OCN 100 Summer 2002 114

HUMIDITY INSTRUMENTS (con’t. ) u SLING PSYCHROMETER – Measure temperature when evaporation causes cooling of a moist surface by ventilation to point where no additional evaporation takes place. ATM OCN 100 Summer 2002 115

Sling Psychrometer (con’t. ) ATM OCN 100 Summer 2002 116

Sling Psychrometer (con’t. ) ATM OCN 100 Summer 2002 117

Inside an Instrument Shelter ATM OCN 100 Summer 2002 118

HUMIDITY INSTRUMENTS (con’t. ) u HYGRISTOR – Measure electrical resistance of a substance which varies with relative humidity. ATM OCN 100 Summer 2002 119

Hygristor on a Radiosonde ATM OCN 100 Summer 2002 120

WATER VAPOR (con’t. ) u Water – – – Vapor Variables vapor pressure mixing ratio dewpoint (& frostpoint) wet-bulb temperature relative humidity apparent temperature/heat index defined as. . ATM OCN 100 Summer 2002 121

WATER VAPOR (con’t. ) u (Water) Vapor Pressure – Partial pressure exerted by water vapor molecules; – Range: 0 mb to 40 mb under normal conditions; – Determined indirectly. ATM OCN 100 Summer 2002 122

WATER VAPOR (con’t. ) u 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 > 65 o. F, human discomfort increases. – ATM OCN 100 Summer 2002 123

WATER VAPOR (con’t. ) u Frostpoint temperature – Saturation point at temperatures below freezing point (T < 0 o. C) when “frost” could be formed. – Frost forms directly through deposition. ATM OCN 100 Summer 2002 124

WATER VAPOR (con’t. ) u 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. ATM OCN 100 Summer 2002 125

WATER VAPOR (con’t. ) u 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. ATM OCN 100 Summer 2002 126

Psychrometric Tables Table A: Relative Humidity [%] Inside cover, Moran and Morgan (1997) ATM OCN 100 Summer 2002 127

Psychrometric Tables Table B: Dewpoint Temperature (C) Inside cover, Moran and Morgan (1997) ATM OCN 100 Summer 2002 128

WATER VAPOR (con’t. ) u Water – – – Vapor Variables vapor pressure mixing ratio dewpoint (& frostpoint) wet-bulb temperature relative humidity apparent temperature/heat index defined as. . ATM OCN 100 Summer 2002 129

WATER VAPOR (con’t. ) u Relative – – – Humidity A measure of the relative closeness to saturation conditions; Requires specification of air temperature; RH = 100% at saturation (i. e. , dewpoint). ATM OCN 100 Summer 2002 130

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

WATER VAPOR (con’t. ) ATM OCN 100 Summer 2002 132

WATER VAPOR (con’t. ) ATM OCN 100 Summer 2002 133

Diurnal Variation in Relative Humidity See Fig. 6. 5 Moran & Morgan (1997) NOTE: Dewpoint ranged between 8° to 9° C during day ATM OCN 100 Summer 2002 134

WATER VAPOR (con’t. ) u 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. ATM OCN 100 Summer 2002 139

Apparent Temperature (°F) – Heat Index From NWS ATM OCN 100 Summer 2002 141

Late Sunday Afternoon Temperatures (o. F) ATM OCN 100 Summer 2002 143

Late Sunday Afternoon Dewpoints (o. F) ATM OCN 100 Summer 2002 144

Late Sunday Afternoon Apparent Temperatures/Heat Indices (o. F) ATM OCN 100 Summer 2002 145

Announcements u Homework #3 is returned today Answer Key is posted at http: //www. aos. wisc. edu/~hopkins/aos 100/homework u Homework #4 is due Thurs. u 2 nd Hour Exam is scheduled for Thurs. u Study sheet is posted at: http: //www. aos. wisc. edu/~hopkins/aos 100/exams u If you have ? ? , please see me. ATM OCN 100 Summer 2002 146

WATER VAPOR (con’t. ) u Climatology of Atmospheric Humidity – tropical vs. polar – maritime vs. continental ATM OCN 100 Summer 2002 148

Rule of thumb u When: – Air temperature falls to within 2 to 3 Fahrenheit degrees of dewpoint and – Winds are light u Then: – Fog often forms. ATM OCN 100 Summer 2002 153