Preamble to Chapter 05. Hydrologic Cycle Intro. Ocean and Freshwater Distribution. Chapter 5: Atmospheric Water and Weather

Transcription

1 Chapter 5: Atmospheric Water and Weather Preamble to Chapter 05 Hydrologic Cycle Intro Quantity Equilibrium: Water at a relative balance over the last 2 billion years Diagram of the hydrologic cycle Ocean and Freshwater Distribution Note: this chapter s concepts are primarily concerned with the tiny fraction of water that is in the atmosphere Older Figure 5.3 1

2 Three States of Water Good Concepts: Phase Changes Sublimation/Deposition Melting/Freezing Vaporization/Condensation Figure 5.2 Phase Changes: Solid, Liquid, Vapor Figure 5.4 Relative Humidity: Daily Flux Figure 5.6 Unsaturated Saturated 2

3 Exhaust from the stack enters cold air below the dewpoint, and immediately condenses Dewpoint Water Vapor in the Atmosphere Invisible to the naked eye, water vapor can be sensed using devices that monitor infrared wavelengths A useful piece of information for weather forecasters Figure 5.9 (old textbook) Typical Daily Humidity and Temperature Patterns Premise: specific humidity does not change, but relative humidity does shift in response to diurnal cooling and heating of planetary surface Graph of hypothetical temperature and humidity pattern throughout a particular solar day Figure 5.8 3

4 Vapor Pressure of Water The fraction of the atmosphere s total pressure that is from water vapor As the atmosphere approaches saturation at any particular temperature, the relative humidity will increase until the air simply cannot contain more water vapor... condensation must then occur If condensation nuclei are present Figure 5.9 Maximum Specific Humidity As temperature increases, the capacity of an air parcel or air mass to contain water vapor also increases Figure 5.10 Buoyancy and Gravity Older Figure

5 Adiabatic Cooling: Air Parcel Rises and Expands Adiabatic Cooling Figure 5.12 Adiabatic Heating: Air Parcel Descends and Compresses Adiabatic Heating: Air Parcel Descends and Compresses Figure 5.12 Adiabatic Process Rates Dry adiabatic rate (for unsaturated air) 10 C / 1000 m 5.5 F / 1000 ft Moist adiabatic rate (for saturated air) 6 C / 1000 m 3.3 F / 1000 ft 5

6 Unstable Conditions 1 Unstable: air is warmer than environmental air, less dense, so rise occurs ELR is lower than the air parcel at all altitudes in the diagram, allowing the air parcel to rise up until it finally cools to the environmental temperature Figure 5.13 Unstable Conditions 2 Russell, Kansas: Summer 2003 Stable Conditions 1 Stable: air is cooler and denser than environmental air, tendency to descend ELR is higher than the air parcel s, meaning that the parcel has no physical motive for ascent into the atmosphere Figure

7 Stable Conditions 2 Lewiston, Idaho: Spring 2004 Stable and Unstable Atmospheric Conditions Absolutely Stable: ELR < MAR Absolutely Unstable: ELR > DAR Conditionally Unstable: MAR < ELR < DAR Older Figure 5.13 Condensation Nuclei: Dust Smoke Salt Pollen Bacteria Skin cells Microscopic particles Condensation Nuclei 7

8 Precipitatio n Formation Collision and coalescence process: Tropical pattern Ice crystal process: Extratropical pattern Snow Rain Sleet Freezing Rain Basic Types of Precipitation The type of precipitation experienced in any location depends on the vertical profile of atmospheric temperatures Cloud Types and Identification Figure

9 Nomenclature Roots Cloud Roots: combinations provide basic cloud meanings cirraltonimbcumulus stratus high-level clouds middle-level clouds clouds actively precipitating puffy-shaped clouds layered clouds Cirrus Figure 5.15 Can signal that bad weather is on the way Cirrocumulus Figure 5.15 A good sign that precipitation is coming, not necessarily severe rain 9

10 Cirrostratus Figure 5.15 When these thicken, they often signal rain/snow in hours Altocumulus Figure 5.15 Appearing in the morning of a hot, humid day may bring afternoon storms Altostratus Figure 5.15 These often arrive ahead of widespread rain/snow, such as regional storms 10

11 Stratus Figure 5.15 Gray skies from horizon to horizon that may bring mist, but not rainfall Nimbostratus Figure 5.15 Sun not visible through clouds and fog; active precipitation Lenticular Lenticular 1 Figure

12 Mountain Wave Clouds Lenticular a.k.a. Wave cloud formation Lenticular cloud & Mt. Shuksan, Washington Cascades Lenticular 2 Complex cloud structures, Mount Shasta Complex Orographic Clouds 12

13 Cumulus Figure 5.15 Generally fair weather unless vertical development continues Cumulonimbus Figure 5.15 Often preceded by a Cirrus deck, potentially severe rain/hail storm Advection Fog Cool coastal waters near San Francisco chill the air to the dewpoint Fog then moves horizontally onshore Figure

14 Evaporation Fog Figure 5.18 Figure 5.25 Valley Fog: Dense, cooler air pooling in low-lying areas Valley Fog Radiation Fog Figure

15 Fog Redux Fog is just a low-flying cloud a cloud at the Earth s surface Foggy Forest Air Masses Colder air invades from arctic and polar zones in winter season Warmer air intrudes from subtropics during summer season Figure

16 North American Air Masses 1 Figure 5.20 North American Air Masses 2 Figure 5.20 Global Air Masses Global distribution of air mass source regions c = continental m = maritime E = equatorial T = tropical P = polar A = Arctic AA = Antarctic 16

17 Convergent Lifting Zone of low pressure within an air mass, such as the process of intertropical convergence The bottoms of clouds are found at the altitude of the dewpoint temperature, or what is known as the lifting condensation level Figure 5.22 Convectional Lifting Air parcel or air mass lift due to localized or regionalized surface heating trends Figure 5.22 Orographic Lifting Air parcel or air mass lift due to the mere presence of a mountain (single or chain) in the path of winds Figure

18 Frontal Lifting Air parcel or air mass lift that occurs as different air mass systems collide Figure 5.22 Orographic Lifting Western side of the Cascades: Eastern slopes of the Cascades: - windward side of the range - leeward side of the range - orographic enhancement - rainshadow effect Figure 5.24 Oregon s Mountain Barriers 18

19 Frontal Lifting Cold Fronts Cold air forces warm air aloft 400 km wide (250 mi) Warm Fronts Warm air moves up and over cold air 1000 km wide (600 mi) Cold Front Figure 5.26 A cold front is composed of cool, stable air that stays close to the surface and forms a wedge-shape that forces its way into the zone of warmer air. The colder air moves in relatively quickly and can generate thunderstorms as it creates frontal uplift, cloud formation, and possibly precipitation close to the location of the frontal boundary. Warm Front Warm fronts form as relatively warm air advances into a zone occupied by relatively cold air; the warm air gradually replaces the cold air across the area. Ahead of the frontal boundary, clouds form in a predictable pattern and precipitation occurs ahead of the frontal activity; the warm air overruns and forces out the cold air slowly. Figure

20 Frontal Variation Fronts can vary in size, depth, and velocity, which is partly why storm systems vary Life Cycle of a Midlatitude Cyclone Stationary stage Cyclogenesis Open wave stage Occluded stage Dissipating stage Life Cycle and Fronts 1: Stationary 2: Cyclogenesis 3: Open Wave 3: Open Wave 4: Occluded 5: Dissipating 20

21 Cyclone Weather Map GIA 5: pp Older Figure 5.29 Thunderstorm Occurrences Figure 5.30 Typical thunderstorm activity and generalized internal winds Thunderstorm Internal Winds 21

22 Thunderstorm-derived Hail Thunderstorm Stages Cumulus stage: no active precipitation leaves the storm system Mature & Dissipating: active precipitation; cumulonimbus clouds Thunderbolts Positive ions collect in & the crown Lightning of the storm Negative ions collect in the base of the storm When enough charge builds up, a bolt of lightning occurs 50,000 degrees Fahrenheit 1.5 million volts 0.2 seconds 22

23 Squall Line & Derechos Squall line: multiple thunderstorm cells Storm Tracks Figure 5.34 (old textbook) Tropical Cyclones Tropical Cyclones, Global Map Figure

24 View of Tropical Cyclone Hurricane Isabel Tropical Cyclones, Structure Figure 5.37 Tropical Cyclone Complex Eye of the hurricane is essentially surrounded by bands of thunderstorms 24

25 NE Side: storm track + wind vector higher winds; storm surge; more damage Tropical Cyclone Spatial Link SW Side: storm track wind vector slower winds; less damage Variations on a Cyclone Fuel source Cyclonic movement Forms of precipitation Spatial area of influence Spatial impacts Tornado Map & Seasonal Timing Spatial and temporal patterns of tornadic activity in the U.S. Figure

26 Tornado Formation Tornado Formation 1 Stronger upper-level winds overrun slower friction-level winds, creating a form of uplift results in the formation of a mesocyclone, which has the potential to shoot tornado funnels down to the surface Figure 5.33 (from Geosystems and Elemental Geosystems) Tornado Formation 2 Tornado Spatial Link Quite dangerous, but damage tends to be focused on smaller spatial areas 26