Atmospheric Heat and Humidity Atmospheric heating Heat is always transferred from warmer to cooler objects Mechanisms of heat transfer Conduction Convection Radiation electromagnetic radiation Mechanisms of heat transfer Figure 16 16 The electromagnetic spectrum Figure 16 17 Average distribution of incoming solar radiation Figure 16 19 The heating of the atmosphere Figure 16 21 Temperature measurement Daily maximum and minimum Other measurements calculated from these Daily mean temperature Daily range Monthly mean Annual mean Annual temperature range Weather instrument shelter North America isotherms Controls of Temperature Day length Sun angle Land water relationship Geographic position relative to general circulation of the atmosphere and ocean Altitude Cloudiness Land water relationship Water moderates the temperature Warmer winters and cooler summers near large bodies of water Temperature comparison Seattle Spokane Temperature comparison Vancouver Winnepeg Temperature comparison Eureka NYC Changes in temperature with change in elevation Two different mechanisms Earth s atmosphere is heated from below Gases cool as they expand Earth s atmosphere is heated from below It is warmer closer to the sea level It is cooler at higher altitudes Environmental lapse rate About 6 5o C 1000 m About 3 5o F 1000 ft Temperature comparison Quito Guayaquil General circulation of the atmosphere Geographic position Western sides of ocean basins get equatorial heat from ocean currents More moderate winter temperatures on east coasts of continents Eastern sides of ocean basins have cold polar currents Cooler year round temperatures on west coasts of continents Cloudiness Daytime clouds shade surface reflect energy away from area Nighttime clouds blanket area reflect heat energy back toward Earth s surface Cloudy day Cloudy night January temperature July temperature Jan and July temps Latent Heat of Water Heat energy that water releases or absorbs when it changes phase Gains it from environment as it melts or evaporates So it cools the environment Loses it when it freezes or condenses So it warms the environment Latent heat of water Frost on window Humidity Description of how much water air contains Relative Humidity compares how much moisture is in the air to how much moisture the air could hold The amount of water that air can hold is a function of temperature Relative humidity lowering temperature Humidity temperature daily trend Dew on spiderweb Changes of humidity Can warm or cool air and not change water content Will result in different relative humidity Can increase or decrease water content of air without change in temperature Relative humidity constant temperature Sling psychrometer Changes in temperature with change in elevation Two different mechanisms Earth s atmosphere is heated from below Gases cool as they expand Gases cool as they expand Still have same heat energy Take up larger volume Increase in volume at lower pressure Atmospheric pressure declines with altitude Temperature change due to change in volume called Adiabatic lapse rate Adiabatic lapse rate Temperature declines with lowering pressure as air moves to higher altitude Temperature increases with increasing pressure as air moves to lower altitude Adiabatic lapse rate Rate of temperature change depends on saturation Saturated air has condensation of water which releases heat warms environment 10o C 1000 m if not saturated 6o C 1000 m if condensation is occurring Cooling by lifting adiabatics Orographic lifting Rain shadow Warm front lifting Convergent lifting Convective lifting Hot air balloons Stable conditions Conditional stability
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