Hydrologic Cycle. Science Concepts. Surface-Atmosphere Exchange of Water. Evaporation Condensation Precipitation Runoff.

Transcription

1 Hydrologic Cycle 23-1 Surface-Atmosphere Exchange of Water Water Cycle Science Concepts Evaporation Condensation Precipitation Runoff

2 Hydrologic Cycle 23-2 Change in Annual Precipitation

3 Hydrologic Cycle 23-3 Modeled Environmental Water Scarcity Index Scarcity is where the amount of water removed from the system puts the ecosystem at risk by tapping into the environmental water demand, i.e., the amount of water needed to sustain the integrity of the ecosystem Areas above 0.4 are under ecosystem environmental stress Areas higher than 0.8 (orange and red) are highly-stressed environmentally

4 Hydrologic Cycle 23-4 The Water Cycle All streams flow into the sea, yet the sea is never full. To the place the streams come from, there they return again. Ecclesiastes 1:7 (New International Version)

5 Hydrologic Cycle 23-5 The Water Cycle m 3 per year

6 Hydrologic Cycle 23-6 GOES Water Vapor Image

7 Hydrologic Cycle 23-7 GOES Visible Image

8 Hydrologic Cycle 23-8 Mean Global Precipitable Water (cm) Annual Average

9 Hydrologic Cycle 23-9 Mean Global Precipitable Water (cm) (Con t) Seasonal variability S.W. Seemann, J. Li, W.P. Menzel Univ. Univ. Wisconsin, NOAA

10 Hydrologic Cycle Amazon Seasonal Variability Note seasonal rainfall variability Study/AmazonLAI/ Amazon and Tropical seasons revolve around wet/dry not hot/cold

11 Hydrologic Cycle Honolulu WSO Airport Ave. Max. Temp. = 84.0 F 21 20ʼ N, ʼ W Ave. Min. Temp. = 70.2 F Elevation = 10 ft Averages for 10/1/49-3/31/05 Ave. Annual Precipitation = in climain.pl?hihono

12 Hydrologic Cycle Mean January Moisture Dewpoint Temperature ( F) Relative Humidity (%) cgi-bin/climaps/climaps.pl

13 Hydrologic Cycle Mean July Moisture Dewpoint Temperature ( F) Relative Humidity (%) cgi-bin/climaps/climaps.pl

14 Hydrologic Cycle Average Dewpoint Temperature ( F) ( ) January July Annual cgi-bin/climaps/climaps.pl

15 Hydrologic Cycle July Dewpoint Temperature & Diurnal Temperature Range ( F) Dewpoint Temperature Diurnal Temperature Range cgi-bin/climaps/climaps.pl

16 Hydrologic Cycle Average Relative Humidity ( ) January July Annual cgi-bin/climaps/climaps.pl

17 Hydrologic Cycle Average Annual Precipitation ( ) Annual broadcastmet/watershed/media/ graphics/unit_6/nat_atlas_precip.jpg

18 Hydrologic Cycle Surface-Atmosphere Exchange of Water (Conʼt) Saturation Processes Increase Vapor Cooling Lifting Mixing Radiational Cooling Science Concepts Dry Adiabatic & Moist Adiabatic Process Condensation Types Dew/Frost Fog Haze Cloud Droplets

19 Clouds and Precipitation Atmospheric Saturation Processes Add moisture - Infrequent (Steam Fog) Cool to dewpoint temperature - Usual process - Lifting - Mixing - Radiation

20 Clouds and Precipitation Cloud Formation Condensation process - Condensation nuclei > What are they? Sea salt Combustion products - smoke Dust - Clay from plowed fields Science quotes of 5th and 6th graders - I am not sure how clouds get formed. But the clouds know how to do it, and that is the important thing. > What is their distribution? Decrease with height - For Example: 0.1 as many at 3,000 ft as at surface; 0.01 as many at 14,000 ft as at surface More over cities than country More over land than ocean - More giant nuclei over oceans - Hygroscopic nuclei - Begin to attract water vapor at RHs as low as 70% > What are they? Sea salt - Most common

21 Clouds and Precipitation Types of Condensate Dew - Caused by radiational cooling of a surface to the dewpoint temperature of the air - Typical conditions Science quotes of 5th and 6th graders - Dew is formed on leaves when the sun shines down on them and makes them perspire. > Clear skies > Calm winds (little mixing) > Nighttime - Dewpoint temperature above 32 F

22 Clouds and Precipitation Types of Condensate (Con t) Frost Quote - Caused by radiational cooling of a surface to the dewpoint temperature of the air - Typical conditions > Clear skies > Calm winds (little mixing) > Nighttime - Dewpoint temperature below 32 F Teg weather report on the car radio had predicted a low of 35 degrees, and Pittmen believed it, seeing frost come out of his mouth. David Morrell, "Desperate Measures" (p. 295) What is wrong with this statement?

23 Clouds and Precipitation Types of Condensate (Con t) Fog - Defined as a cloud on the ground - Caused by > Cooling of the air to its dewpoint temperature Most common cause Types of cooling fog Radiation fog Advection fog Upslope fog > Evaporation of enough water to saturate the atmosphere Least frequent cause Types of evaporation fog Steam fog Warm-rain fog - Dissipation ( burns-off ) by solar heating the surrounding ground; causes mixing at edges - Annual average days with fog In order to save the army during the Revolutionary War Washington retreated from Long Island overnight on Aug. 29, By sunrise on the 30th not all the troops had been ferried across the river to the NY side. However, a heavy fog had settled over the river so they could continue to cross without being observed by the British troops and war ships. Within an hour after the boats had carried the last of the 9,000 troops safely across, the wind shifted and the fog dispersed. Fog had helped save the army. 1776, David McCullough, pp

24 Clouds and Precipitation Radiation and Valley Fog Alabama Rivers Note contrails Bright yellow is fog Valley fog AVHRR Satellite - 4 November Color enhanced (Visible, near infrared (~1 micron), infrared (~3.7 micron)

25 Clouds and Precipitation Types of Condensate (Con t) Haze - Caused by particles ( large ) that scatter all wavelengths of light equally - Increases as RH becomes greater than 70% because of hygroscopic nuclei Cloud droplets - Cooling of the air aloft to its dewpoint temperature

26 Hydrologic Cycle Surface-Atmosphere Exchange of Water (Conʼt) Precipitation Physics (Conʼt) Cloud Growth Processes Droplet Multiplication Cascade Effect Science Concepts Surface Tension Solute Effect Curvature Effect

27 Clouds and Precipitation Cloud Droplet Growth Processes Solute effect - Solution of water and nuclei material - Helps droplet grow - Decreases as droplet becomes larger - Larger condensation nuclei, larger this effect. Thus, larger nuclei grow larger droplets Curvature effect - Caused by surface tension around droplet Science quotes of 5th and 6th graders - To most people solutions mean finding the answers. But to chemists solutions are things that are still all mixed up. - Hinders droplet grow - Decreases as droplet becomes larger Cloud Droplet Multiplication Process Cascade effect - Large drops break into several smaller drops

28 Hydrologic Cycle Surface-Atmosphere Exchange of Water (Conʼt) Precipitation Physics (Conʼt) Rain Drop Formation Collision and Coalescence Process Bergeron Process Precipitation Types Science Concepts Terminal Velocity Gravitational Force Drag Force Pressure Gradient Force Supercooled Water Saturation Over Water Ice

29 Clouds and Precipitation Forces on a Falling Object Terminal velocity ~120 mph

30 Clouds and Precipitation Forces on a Cloud or Rain Drop Drag Force => Depends on square of Velocity and Shape of Drop Pressure Gradient Force => Depends on Volume of Drop Gravitational Force => Depends on the Mass of the Drop D = C d ρ A V 2 / 2 D = Drag force C d =Drag coefficient (usually determined experimentally) ρ = Density of fluid (air) A = Reference area (includes shape, etc.) V = Velocity Drag Force Cloud or Rain Drop Pressure Gradient Force Gravitational Force

31 Clouds and Precipitation Atmospheric Particles Name Diameter (cm) # per cm 3 Large Ions 10-6 to to 10 4 Smoke and Dust 10-5 to 10-4 variable Large Condensation Nuclei 10-5 to Giant Condensation Nuclei 10-4 to Cloud Droplets 10-4 to 10-2 Rain Drops 10-2 to 1

32 Clouds and Precipitation Particle Terminal Velocities Particle Type Diameter (cm) m/s mph Condensation Nuclei 2 X X X 10-7 Small Cloud Droplets 1 X X 10-3 Typical Cloud Droplets 2 X X X 10-2 Large Cloud Droplets Small Rain Drops Typical Rain Drops Large Rain Drops

33 Clouds and Precipitation Raindrop Growth Process Raindrop 100 times larger diameter than cloud drop; 1,000,000 time larger volume How does this tremendous growth occur? - Coalescence process - Warm clouds > Terminal velocity Gravitational force Pressure gradient force Drag force > Large drops fall faster than smaller drops > Large drops collect smaller drops Did you know - Houses used to have thatched roofs - thick straw, piled high, with no wood underneath. Because it was the a place animals could get warm, cats and other small animals (mice, bugs) lived in the roof. When it rained, the thatch became slippery and sometimes the animals would slip off the roof. Hence, the saying "It's raining cats and dogs."

34 Clouds and Precipitation Raindrop Growth Process (Con t) Raindrop 100 times larger diameter than cloud drop; 1,000,000 time larger volume (Conʼt) How does this tremendous growth occur? (Conʼt) - Bergeron-Findeisen or ice process - Cold clouds > Freezing nuclei Not enough in the atmosphere Pure water may not turn to ice until -40 C > Between 0 C and -40 C, cloud is mixture of ice and liquid. At temperatures below (i.e., heights above) -40 C, cloud is all ice. > Ice crystals grow at expense of liquid drops

35 Clouds and Precipitation Comparison of Maritime and Continental Rain Clouds Maritime Continental Number of Nuclei 940 cm cm -3 Droplet Concentration 50 cm cm -3 Median Droplet Diameter 17 x 10-6 m 11 x 10-6 m

36 Clouds and Precipitation Precipitation Classification Drizzle - Small, numerous drops falling out of fog or low layer stratus clouds - Indicative of stable stratification with little vertical motion Intermittent or Continuous Precipitation - Rain or snow - Falling more or less evenly from altostratus or nimbostratus clouds - Caused by widespread and slow upward movement of large masses of air Showers (Squalls, Flurries) - Precipitation with short duration with fair intervals - Caused by cumulus or cumulonimbus clouds, i.e, convection - Indicative of unstable stratification with fairly strong upward vertical motion in localized regions

37 Clouds and Precipitation Types of Precipitation Virgae - Rain that evaporates below cloud base, but before reaching the ground Rain - Lower atmosphere above freezing - Drops large enough to fall relative to air motions /tstms.htm

38 Clouds and Precipitation Types of Precipitation Freezing Rain - Ground at 0 C or colder Very shallow layer of air near the ground at near 0 C or colder Layer of air above this shallow layer at temperatures above 0 C (Gh)/guides/mtr/cld/prcp/zr/frz.rxml

39 Clouds and Precipitation Types of Precipitation Sleet, Grauple, Ice Pellets - Clear ice drops - Precipitation is in the form of liquid drops at sometime as it falls - Deeper layer of air above the ground at 0 C or colder - Layer of air above this deeper layer at temperatures above 0 C (Gh)/guides/mtr/cld/prcp/slt.rxml

40 Clouds and Precipitation Types of Precipitation (Con t) Science quotes of 5th and 6th graders - A blizzard is when it snows sideways. Snow - Opaque ice crystals or flakes - Crystals form at temperatures below 0 C by the process of deposition - No liquid phase - Ground at or near 0 C or colder - Layer of air above the ground at temperatures below 0 C (Gh)/guides/mtr/cld/prcp/snow.rxml html

41 Clouds and Precipitation Types of Precipitation (Con t) Hail - Large balls or lumps of ice - Often formed of concentric rings of clear and opaque ice - Formed in clouds with strong updrafts, i.e., convective clouds hail.html Record Hail Stone - 7 diameter, 18.75ʼʼ circumference fell in Aurora, NE, 22 June html