GEOG 1290 Section H F2024 Atmospheric Water and Precipitation PDF

Section H. Atmospheric Water and Precipitation Introduction to Physical Geography GEOG 1290 Department of Environment and Geography University of Manitoba Janna Wilson and Lisa Ford  Copyright Lecture slides, course notes, and ed...

Section H. Atmospheric Water and Precipitation Introduction to Physical Geography GEOG 1290 Department of Environment and Geography University of Manitoba Janna Wilson and Lisa Ford  Copyright Lecture slides, course notes, and educational resources are copyright-protected and made available to you for your personal educational use and private study only. Unless stated otherwise, further copying and distribution of these materials is strictly prohibited. © Janna Wilson & Lisa Ford, 2024. Further electronic or hard copy reproduction and or distribution of this content in part or in whole is strictly prohibited. Section H. Atmospheric Water and Precipitation H.1 The Hydrological Cycle H.2 Properties of Water H.3 Atmospheric Humidity H.4 Cloud Formation and Classification H.5 Precipitation  H.1 The Hydrologic Cycle Learning Objectives Explain what the hydrologic cycle is & why it is important. Explain the concept of the hydrosphere.  Hydrosphere Hydrosphere: global water system Key role in redistributing energy flows via atmospheric/oceanic circulation Powered by radiant energy from the sun Global Distribution 97.2% Saline 2.8% Freshwater Figure 9-1 Moisture inventory of Earth (Hess and Finch, 2022, p. 258)  The Hydrologic Cycle Movement of water between various storage locations (reservoirs) Amount of water is finite Total amount evaporated equals the total precipitated globally local and regional imbalances occur Figure 9-2 The hydrologic cycle (Hess and Finch, 2022, p. 258)  H.2 Properties of Water Learning Objectives Discuss the physical states & physical properties of water & the significance of latent heat to water’s phase changes.  Properties of Water - Hydrogen Bonding Hydrogen Bonding Bond between H2O molecules due to slightly -ve O charge & slightly +ve H charge Figure 4 Hydrogen and covalent bonds (https://bit.ly/3jFCSVK) Cohesion H2O molecules attracted to each other Adhesion H2O is attracted to another substances Figure H.2.a Cohesion/Adhesion (https://on.doi.gov/3f0U5oP)  Properties of Water – Thermal Characteristics As water (H 2O) cools: Contracts when cooling to 4 oC Expands by ~9% between 4 - 0 oC Ice floats on water - less dense compared to liquid water Expansion important in weathering of rock Specific Heat amount of energy required to raise the temperature of 1 g of a substance by 1 oC Table H.1.a Specific heat of select substances http://www.eoearth.org/article/Global_surface_temperature_distri bution  Properties of Water - Latent Heat Energy that is absorbed (stored) or released when a substance changes state (without a change in temperature) forms or breaks molecular bonds Energy Energy Absorbed Released Melting Freezing Evaporation Condensation Sublimation Deposition Figure 6-4 Phase changes of water accompanied by latent heat exchange (Hess and Finch, 2022, p. 146) Properties of Water - Latent Heat Figure 6-4 Energy input and temperature changes of water (Hess and Finch, 2022, p. 147)  H.3 Atmospheric Humidity Learning Objectives Describe how water vapour enters the atmosphere through the process of evapotranspiration. Compare & contrast the various was of expressing atmospheric humidity. Explain why dew-point temperature is an important variable in the hydrologic cycle.  Evapotranspiration Evaporation: transformation of liquid water into water vapour Transpiration: loss of water vapour directly from leaf pores (stomates) in plants into the atmosphere Evapotranspiration = Evaporation + Transpiration Figure H.3.a Evapotranspiration (Image Credit: Toews, M. W. , CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=2843655  Evapotranspiration Rates Evapotranspiration rates depend on Net radiation which increases heating Air temperature which influences maximum humidity Relative humidity and moisture capacity of air Wind speed Figure 7.13 Wind and Evaporation Vapour (Arbogast et al., 2018, p.156)  Humidity Humidity: amount of water vapour in the air Varies spatially & temporally (supply and demand) Measures of humidity 1. Vapour Pressure 2. Specific humidity 3. Relative humidity 4. Dew-point temperature Precipitable water measurement of how much moisture could theoretically precipitate given the Figure H.3.b Average total precipitable water in the right conditions atmosphere (https://www.nesdis.noaa.gov/content/atmospheric- moisture)  Water Vapour Pressure Gradient Water vapor moves along a vapour pressure gradient from high vapour pressure to low vapour pressure Higher vapour pressure is found close to a water surface, and air at higher altitudes has lower vapor pressure Wind can move moist air away from the source Figure 7.14 Water Vapour Gradient (Arbogast et al., 2018, p.156)  Humidity and Air Temperature Warm air can hold much more H2O than cold air Cold dry air can have close to 0% H 2O vapour Warm tropical air may have 4-5% H2O vapour Figure 7.5 Maximum humidity and air Figure H.3.c Mean water vapour density at sea level temperature (Arbogast et al., 2018, p. 149) https://www.atmoswater.com/map-of-the-water-from-air-resource.html  Measuring Water Vapour Specific Humidity (g/kg) Actual amount of water vapour in a given amount of air E.g. 10 grams of H2O vapor in a kg of air Maximum Specific Humidity (g/kg) Maximum amount of H2O vapor that a body of air can hold at its current temperature Figure 4.5 Specific humidity & temperature (Strahler & Merali, 2008, p. 102)  Humidity - The Saturation Curve Saturation curve describes the relationship between maximum humidity and temperature Maximum humidity rises with temperature Figure 6-8 Water vapor capacity increases as temperature increases (Hess and Finch, 2022, p. 150)  Relative Humidity (RH) Percentage of actual H2O vapour in the air compared to the maximum amount the air could hold at that temperature saturation depends on temperature describes how close the air is to saturation at its current temperature Relative humidly can change as: 1. Temperature changes changes the maximum specific humidity. 2. Water vapour changes (gains or losses) changes the specific humidity  Relative Humidity RH = specific humidity/maximum specific humidity x 100 At 100% relative humidity, air is saturated Actual water vapour shown in blue Maximum specific humidity shown in yellow 30°C 20°C RH: 28% RH: 52% 10°C RH: 100% Water Water Water Vapour Vapour Vapour 7.76 g/kg x 100 7.76 g/kg x 100 7.76 g/kg x 100 7.76 g/kg 14.85 g/kg 27.69 g/kg Modified from Figure 8c-1 Relative humidity (Pidwirny, 2016) http://www.physicalgeography.net/fundamentals/8c.html  A parcel of air has a specific humidity of 7.5 g/kg and its air temperature is 30°C. Calculate the relative humidity? A) 12% B) 29% C) 53% D) 34% Specific humidity (g/kg) RH = X 100 Maximum specific Humidity (g/kg) RH = 7.6 g/kg X 100 26 g /kg Figure 4.4 Maximum Specific Humidity (Strahler & Merali, 2008, p. 101)  A parcel of air has a specific humidity of 10.5 g/kg and its maximum specific humidity is 15g/kg. The air temperature is 20°C. Calculate the relative humidity. A) 12% B) 29% C) 53% RH = Specific humidity (g/kg) D) 70% Maximum specific X 100 Humidity (g/kg) RH = 10.5 g/kg X 100 15 g /kg  What is the maximum specific humidity at 0 oC? 4 g/ kg Figure 4.4 Maximum Specific Humidity (Strahler & Merali, 2008, p. 101) Temperature-Relative Humidity Inverse Relationship Temperature and humidity have an INVERSE relationship Heating: temperature increases, relative humidity decreases Cooling: temperature decreases, relative humidity increases Figure 6-4 Inverse relationship between temperature and humidity (Hess and Finch, 2022, p. 151)  Humidity - Global Patterns Lower latitudes: Specific humidity is high/Relative humidity is low Higher latitudes: Specific humidity is low/Relative humidity is high Water Vapour Figure H.3.d Average amount of water vapor in a column of atmosphere in a given month (https://earthobservatory.nasa.gov/global-maps/MYDAL2_M_SKY_WV)  H.4 Cloud Formation and Classification Learning Objectives Describe the properties & formation of cloud droplets. Identify & describe the major cloud types & explain why they occur.  Atmospheric Stability The stability of the atmosphere depends on: 1. Relative temperature 2. Density Temperature of a parcel of air compared with surrounding atmosphere Figure H.4.a Atmospheric stability https://www.weather.gov/jetstream/parcels  Cloud formation Clouds are visible masses of tiny suspended water droplets or ice crystals Two necessary conditions for cloud formation 1. Air must be saturated (100% RH) Either by cooling below the dew point or by adding water vapor to the air 2. There must be a substantial quantity of hygroscopic condensation nuclei (small aerosols) for water vapour to collect e.g. dust, sea-salts (significant source)  Cloud Classification 10 cloud types based on form and height (altitude) Forms 1. Cirro-form 2. Cumulo-form 3. Strato-form 4. Nimbo-form Height (altitude) 1. Low 2. Middle (alto) 3. High (cirrus) 4. Vertically Developed Figure 6-4 Typical shapes and altitudes of 10 major cloud types (Hess and Finch, 2022, p. 159)  Cloud Cumulus Cirrus Stratus Cirrostratus Altocumulus Nimbostratus Figure 6-22 Common types of clouds (Hess and Finch, 2022, p. 160)  Discover…Sun Dogs Caused by the refraction of sunlight by the hexagonal ice crystals in cirrus and cirrostratus clouds Typical when sun is close to the horizon and there are cirrus clouds (or fog) Rainbows caused by sunlight striking liquid drops rather than ice crystals Figure H.5.a Sun Dogs, Fargo North Dakota, Feb 18, 2019. (Photo Credit Gopherboy6956, Public Domain, https://commons.wikimedia.org/w/index.php?curid=5985196  H.5 Precipitation Learning Objectives Define & describe the different types of precipitation & explain how each form. Explain the mechanisms by which rain drops form & increase in size.  Precipitation Forms within clouds when cloud droplets or ice crystals grow large enough to overcome updrafts and fall to Earth Rain: liquid H20 droplets Snow: ice crystals Sleet: rain freezes before hitting the ground Freezing rain: rain freezes on impact with the ground Hail: ice crystals melt and refreeze before falling Virga: rain that evaporates before reaching the ground  Precipitation Water or ice drops must be large/heavy enough to fall through the cloud 1 million cloud droplets needed to from a rain drop heavy enough to fall to earth Raindrop shape is determined drop size air resistance Figure H.6.a Raindrop shapes https://www.usgs.gov/media/images/raindrop-shape-determined-drop-size- and-air-resistance  Lifting Mechanisms All precipitation originates from parcels of moist air that have been adiabatically cooled Condensation and cloud formation start at the lifting condensation level (LCL) Adiabatic cooling occurs through the lifting of air from the surface to higher levels in the atmosphere by: 1. Convective uplift 2. Orographic uplift 3. Convergent uplift 4. Frontal (cyclonic) uplift  Convective Uplift Spontaneous (no external force is applied) Unequal heating of surface causes air parcel to rise & expand Pressure of unstable air ⇣ as it rises (air cools adiabatically) Condensation occurs at LCL Figure 6-33 The four types of atmospheric lifting and precipitation: convective (Hess and Finch, 2022, p. 167)  Orographic Uplift Air forced to rise by a mountain Windward side Air cools at DAR to dew point Clouds Forms (LCL) and air Figure 7.22a Orographic Clouds continues to cool at SAR (Arbogast et al., 2018, p. 169) Leeward side Air descends, warming at DAR Creates rain shadow (dry conditions) Figure 6-33 The four types of atmospheric lifting and precipitation: orographic (Hess and Finch, 2022, p. 167)  Chinook (Foehn) Chinook Wind Occurs when a steep pressure gradient develops in mountainous regions, such as the Canadian Rocky Mountains high pressure on windward side low pressure on leeward side air is warmed adiabatically as it moves over the mountain and down leeward slope The leeward side tends to be very dry, which is known as a rain shadow Called a foehn when it occurs in Europe  Chinook (Foehn) Figure 5-32 Chinook winds (Hess and Finch, 2022, p. 132)  Convergent Uplift Collision of similar air masses moving horizontally associated with low pressure systems at the ITCZ warm moist tropical air rises in Hadley cells NE & SE trade winds converge towards the ITCZ uplift is initiated, energy released which augments the process produces cloud cover and rain Figure 6-33 The four types of atmospheric lifting and precipitation: convergent (Hess and Finch, 2022, p. 167)  Frontal Uplift Frontal Different air masses collide forming a front and uplift of air Figure 6-33 The four types of atmospheric lifting and precipitation: frontal (Hess and Finch, 2022, p. 167)  Assigned Readings: H.6 Acid Rain (Hess & Finch, 2022, p. 172-175) Learning Objectives Identify issues associated with acid precipitation and actions taken to reduce acid precipitation.  References Arbogast, A., Ford, L., and Dagesse, D. (2018). Discovering Physical Geography (Canadian ed.). Wiley. Hess, D., & Finch, R. (2022). McKnight’s Physical Geography, A Landscape Appreciation (13th edition). Pearson. Hess, D., & Tasa, D. (2014). McKnight’s Physical Geography, A Landscape Appreciation11 th edition. USA: Pearson. Pidwirny, M. (2006). "Atmospheric Humidity". Fundamentals of Physical Geography, 2nd Edition. Retrieved July 27, 2020, from http://www.physicalgeography.net/fundamentals/8c.html The NOAA National Environmental Satellite, Data, and Information Service (NESDIS). (2020). Retrieved from the Atmospheric webpage, July 25, 2020, from https://www.nesdis.noaa.gov/content/atmospheric-moisture. Strahler, A. & Merali, Z. (2008). Visualizing Physical Geography. Wiley Visualizing. Shiklomanov, I. (1993). "World fresh water resources" in Peter H. Gleick (ed.). Water in Crisis: A Guide to the World's Fresh Water Resources, Oxford University Press. Grenci, L., Nese, J, & Babb, D.(2006) A World of Weather: Fundamentals of Meteorology: A Text/Laboratory Manual (4 th ed), Kendall-Hunt Publishing Company.