chapter_06 - The Cryosphere The Chapter 6 Dr Emily Berndt...

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Unformatted text preview: The Cryosphere The Chapter 6 Dr. Emily Berndt Fundamentals of the Climate System EAS 253 I. Introduction I. a. Water in all forms (Oceans, clouds, polar ice) i. ii. Dominates the global energy balance Plays a role in shaping climate a. Cryospthere: all forms of frozen water at Cryospthere: Earth’s surface (except ice clouds) I. Introduction I. c. Primary components of the crysophere i. Continental ice sheets ii. Ice shelves iii. Mountain glaciers iv. Sea Ice v. River and lake ice vi. Snow cover vii. permafrost I. Introduction I. d. Interaction with the climate system i. Changes in the distribution of sea ice and snow cover 1. Change in albedo 2. Creates a feedback to regional and global temperature ii. Changes in the amount of glacier ice impact sea levels iii. Melting of permafrost releases greenhouse gases iv. Sea ice formation 1. Increases salinity 2. Bottom water formation 3. Produce thermohaline circulation v. Sea ice and permafrost impact ecosystems vi. Mountain snow cover and glaciers are a source of freshwater 1. 75% of Western USA water supply 2. acts as a large reservoir I. Introduction I. e. The major components (glaciers, ice e. sheets, and sea ice are constantly in motion motion f. The extent of the crysophere changes on f. time scales from days to millennia time II. River/Lake Ice, Seasonal Snow Cover, and Permafrost Cover, a. Freezing and thawing of rivers/lakes i. ii. Important role in local ecosystems Minor role on global scale processes II. River/Lake Ice, Seasonal Snow Cover, and Permafrost Permafrost b. Formation of Snow i. Snow forms as ice crystals in clouds ii. Freezing nuclei iii. Dominate process is deposition (vapor to solid) iv. When there are no freezing nuclei -Pure water won’t freeze until -40°C i. ii. When temperature drops to 0°C the cloud is a mixture of super When cooled droplets and ice crystals cooled As temperature drops; saturation vapor pressure (SVP) with respect As to ice decreases to 1. 2. 3. 4. Max difference in SVP between ice and water is at -12° to -16°C Air is supersaturated with respect to ice nut the air is unsaturated with Air respect to water respect Vapor deposits directly to ice Ice crystals flow at expense to super cooled droplets Tiny SVP Difference between Water & Ice Solid ice holds molecules better than liquid water Water molecules escape or evaporate easier from droplets than ice crystals Ice Crystals Grow at the Expense of Droplets Saturation vapor Saturation pressure of ice crystals < water droplets water Difference in vapor pressure causes vapor to move or “diffuse” towards the ice crystal towards The result is that the ice crystal grows at the expense of the water droplets droplets Further Growth of Ice Crystals… Further Ice crystals need to grow large enough to Ice overcome the updraft to fall out of the cloud overcome Accretion – growth by collision with supercooled water droplets supercooled Aggregation – ice crystals collide and stick together together Ice Crystal Habit (Shape) c. Northern Hemisphere Snow Cover i. ii. iii. iv. II. River/Lake Ice, Seasonal Snow Cover, and Permafrost and Snow over varies by season Albedo of 80-90% Ice crystals absorb and scatter all visible wave lengths equally Impact on regional energy balance 1. Little radiation absorbed to heat snow Snow persists 2. 3. 4. 5. 6. - Radiation is reflected away instead of heating the surface Regional temperature decreases Can cool air mass above Slows the temperature increase from winter to spring Low thermal conductivity Reduces heat loss from ground to the atmosphere 7. Old snow (density increases) 1. 2. Insulateing properties decreasing Albedo decreases II. River/Lake Ice, Seasonal Snow Cover, and Permafrost and d. Permafrost i. Permanently frozen ground ii. Ground is at or below 0°C for ~2 years iii. Pockets of unfrozen ground (Tallik) iv. Heated from below, cooled from surface v. Surface temperatures fluctuate seasonally 1. 2. Active layer freezes in winter and melts (thaws) in summer Base of permafrost lifts and lowers vi. Temperature profile gives an indication of the longer term Temperature temperature change temperature III. Glaciers and Ice Sheets III. ...
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