PHYC40050-L03-Water

PHYC40050-L03-Water - Climate, Climate Change Nuclear Power...

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Unformatted text preview: Climate, Climate Change Nuclear Power and the Alternatives Climate, Climate Change Nuclear Power and the Alternatives PHYC 40050 Peter Lynch Meteorology & Climate Centre School of Mathematical Sciences University College Dublin PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics MOISTURE Lecture 3 Water in the Atmosphere • Water vapor constitutes only a small fraction of the atmosphere. • Varies from 0% to about 4% • Water is probably the most important gas in the atmosphere for understanding atmospheric processes. • The source of atmospheric water is evaporation PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Satellite picture of clouds over North America, 9 January, 1998 Crumpled steel electrical transmission towers – Canada, January, 1998 PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics p. 83 1 Sequence of events leading to saturation of water vapour in air OBSERVATIONS OF VAPOUR PRESSURE AS A FUNCTION OF TEMPERATURE PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics HUMIDITY Humidity describes the amount of water Humidity vapor in the air. Humidity is described quantitatively as Humidity vapour pressure, absolute humidity, pressure, mixing ratio and relative humidity. humidity. Saturation is achieved when the number of Saturation water vapor molecules leaving a water surface is equal to the number returning from the atmosphere to the water surface. PHYC 40050 Environmental Physics HUMIDITY Saturation vapour pressure is the pressure Saturation exerted by the water vapour at saturation. Absolute humidity is the mass of water per Absolute unit volume . Units are usually grams per cubic meter. Mixing ratio is the mass of water vapor in Mixing an unit mass of air. Usually in grams per kilogram. Relative humidity is the actual amount of Relative water vapour in the air over the amount of water vapour required for saturation. PHYC 40050 Environmental Physics Climatology of hourly temperature and relative humidity PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics 2 When the temperature of the air around this web cooled to the dew point temperature, dew formed, making the web more visible RELATIVE HUMIDITY Relative humidity changes as daily Relative temperature changes. It changes from one location to another. It It changes when air moves vertically in It the atmosphere. Daily variation of temperature and Daily relative humidity However the water vapour content of the However air can stay the same. Dew point is the temperature at which Dew water vapour will condense out of the atmosphere – frost point. PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Temperature (°C) Relative Humidity Mixing Ratio (g/kg) Vapor Pressure (mb) Sat. vapor pressure (mb) Dew point Temp. (°C) Dew point depression (°C) -10 25 -10 75 20 25 3.67 5.87 23.47 -0.5 20.5 20 75 11.1 5 17.6 0 23.4 7 15.6 4.4 PHYC 40050 Environmental Physics 0.45 1.35 0.72 2.16 2.88 2.88 -26.2 -13.5 16.2 3.5 Heat index table PHYC 40050 Environmental Physics CONDENSATION AND DEPOSITION Curvature effect – even if air is saturated Curvature over a flat surface, it may not be for a curved surface. Supersaturation – relative humidity can Supersaturation be above 100% without condensation Nucleation – droplets usually form around Nucleation particles – condensation nuclei. Condensation nuclei can be hydroscopic Condensation or hydrophobic. Ice nuclei. Ice PHYC 40050 Environmental Physics Fig. 4-7, p. 93 PHYC 40050 Environmental Physics 3 STEAM FOG ADVECTION FOG PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics FOG FORMATION Fog defined as a cloud with its base at Fog or near the ground. Fogs result when air is cooled or by Fogs the addition of water vapour to cause saturation. Radiation fog – cooling of surface by Radiation emission of thermal radiation. PHYC 40050 Environmental Physics FOG FORMATION Advection fog – warm and moist air Advection blown over a cool surface. Needs turbulence at the surface. Evaporation/steam fog – air picks up Evaporation/steam additional water over water surfaces. Upslope fog – air is cooled as it flows Upslope up a slope. PHYC 40050 Environmental Physics Lifting Mechanisms that form Clouds Air raised to the Lifting Condensation Level (LCL) becomes saturated. Four mechanisms that cause air to ascend Orographic lifting Orographic Frontal lifting Frontal Convection Convection Convergence Convergence PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics 4 “The Cloud” – Percy Bysshe Shelley I am the daughter of Earth and Water, And the nursling of the sky I pass through the pores of the ocean and shores; I change but I cannot die. For after the rain when with never a stain The pavilion of Heaven is bare, And the winds and sunbeams with their convex gleams Build up the blue dome of air, I silently laugh at my own cenotaph, And out of the caverns of rain, Like a child from the womb, like a ghost from the tomb, I arise and unbuild it again. PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Major cloud types arranged by altitude. Cirrostratus clouds showing halo around the sun Cirrus Clouds PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Cirrocumulus clouds HIGH CLOUDS Above 6000 meters Above Three main types Three Cirrus - detached clouds composed of Cirrus delicate icy filaments, have some vertical extent (mares’ tails) Cirrostratus - transparent cloud veil Cirrostratus produces a halo around the sun or moon. Cirrocumulus - very small cells or ripples Cirrocumulus mackerel sky High clouds can be a portend of stormy High weather Mackerel scales and mares' tails Mackerel make tall ships carry low sails PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics 5 Altocumulus clouds MIDDLE CLOUDS 2000 to 6000 meters. 2000 Composed of water droplets Composed Altocumulus - large patches Altocumulus composed of rounded masses or rolls. Altostratus - formless layer of grayish Altostratus clouds covering all or a large portion of the sky PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Cumulus clouds Cumulonimbus Towering Cumulus PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics SEPARATOR. PRECIP follows. PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics 6 PRECIPITATION GROWTH Cloud droplets are typically 10 microns in Cloud size. Small raindrops are typically 1000 microns (~almost one million droplets) Raindrops grow by two processes Raindrops (1) Collision-coalescence – warm clouds. (1) Collision(2) Bergeron process – cold clouds. (2) Collisioncoalescence process In the Bergeron process snow/ice In crystals are formed – mid-latitude clouds midRain at mid-latitudes is the result of the Rain midmelting of the snow/ice as it descends to temperatures above zero PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Bergeron walk Attraction of water vapour to ice versus water PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Saturation vapour pressure over ice and water PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics 7 Process of aggregation Steps in the formation of the precipitation types PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics WARM FRONT PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics FORMS OF PRECIPITATION Rain - droplets of water greater than 0.5 mm in Rain diameter. Droplets smaller than 0.5 mm called drizzle. drizzle. Much rain starts out aloft as ice crystals. Much Snow - ice crystals. If air is cold (low humidity), we get Snow light and fluffy snow (powder). If air is warm than about -5ºC, then we get wet snow (good for snowballs). ºC, Sleet - small particles of ice. Raindrops encounter Sleet freezing air on descent. If freezing not complete freezing rain. Hail - layers of ice form as the hailstorm travels up and Hail down in a strong convective cloud. Rime - formed by freezing of supercooled fog on objects. Rime PHYC 40050 Environmental Physics THE EFFECTS OF AIRFLOW OVER A MOUNTAIN PHYC 40050 Environmental Physics 8 Adiabatic Cooling and Warming Effects of Moisture PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Fig. 3-17, p. 72 PHYC 40050 Environmental Physics Fig. 2.7 Adiabatic Cooling and Warming A rising parcel of air always expands rising As the parcel expands it will cool As Adiabatic process - no heat energy is Adiabatic gained or lost by the parcel The rate of cooling with altitude due to The this process is called the dry adiabatic lapse rate PHYC 40050 Environmental Physics Adiabatic Cooling and Warming Usually the air contains water vapour. Usually vapour. As the parcel rises an altitude will be As reached when the water vapour condenses. But this releases latent heat of But condensation to the air parcel. • Thereafter, the temperaure of the parcel will not fall as much as for dry air. Moist adiabatic lapse rate. Moist PHYC 40050 Environmental Physics 9 Clouds and Precipitation near Mountains As air ascends mountain it cools adiabatically, As clouds form, and precipitation occurs. Above this altitude the relative humidity stays Above at 100% At the peak of the mountain the absolute At humidity is determined by the saturation vapour pressure at -12C. As the air descends its absolute humidity As remains the same as at the peak PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics Clouds and Precipitation near Mountains As the air descends it is compressed, so it As warms Hence the saturation vapour pressure will Hence increase, and the relative humidity will decrease The net effect of the air ascending and The descending the mountain is that the air becomes drier and warmer. warmer. On the island of Hawaii, the west side of On the coast (westerly winds) has rain forests, the eastern side has deserts. PHYC 40050 Environmental Physics THE EFFECTS OF AIRFLOW OVER A MOUNTAIN PHYC 40050 Environmental Physics PREVIEW End of Lecture 3 The EdGCM Climate Model PHYC 40050 Environmental Physics PHYC 40050 Environmental Physics 10 ...
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