GEOG 1114 1st Edition Lecture 11 Outline of Last Lecture Characteristics of Pressure Agents of Atmospheric Motion Patterns Speed of Surface Winds General circulation of the Atmosphere Outline of Current Lecture Continuation of Pressure and Atmospheric motion Atmospheric Moisture Transfer of Water to the Atmosphere Measuring moisture in the Atmosphere Current Lecture Seven Surface Components of the General Circulation Model Subtropical Highs Persistent zones of high pressure 30 degree latitude in both hemispheres Trade Winds Diverge from subtropical highs Exist between 25 degrees N and 25 degrees S latitude Easterly winds southeasterly in Southern Hemisphere northeasterly in Northern Hemisphere Most reliable winds These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Winds of Commerce Heavily laden with Moisture Do not produce rain unless forced to rise If they rise they produce tremendous precipitation and storm conditions Hadley Cell Convection cell Vertical movement of wind from low at the equator to subtropical high Trade complete the cell Intertropical Convergence Zone ITZ Semi permanent band of low pressure Rising air Region of convergence of the trade winds Low pressure Belt near the equator Constant rising motion and storminess in this region Position seasonally shifts more over land than water Doldrums You get a polar front where easterlies and westerlies meet Westerlies coming out of the west Wind system of the midlatitudes Form on pole ward sides of subtropical highs Two cores of high winds aloft Polar Front Jet Stream Subtropical Jet Stream Rosby Waves path takes N S direction take a dip then it becomes a Rosby wave brings cold air down Polar Highs High pressure cells that develop over the poles build up very cold temperatures produce a thermal high Polar Easterlies Subpolar Lows Low pressure area between polar high and westerlies Air masses conflict between warm westerlies and cold polar easterlies Rising motion and precipitation Contains polar front Modifications of the General Atmospheric Model Latitudinal Shift with Seasons Seven general circulation components shift seasonally Components shift during Northern Hemisphere summer Components shift southward during Southern Hemisphere summer Monsoons Seasonal wind shift Winds onshore during summer Winds offshore during winter Develop due to shifts in the position of the ITCZ Local Winds Continentally Atmospheric Moisture Hydrologic Cycle 1 Water enters atmosphere through evaporation of water from oceans and evapotranspiration from continents 2 Transported as water vapor through the atmosphere by prevailing winds where it condenses into clouds 3 Then when energy and moisture conditions are tight it falls to the earth surface by precipitation 4 Overland stream flow from continents completes this cycle Transfer of water to the Atmosphere Evaporation 1 Transformation of water from a liquid to a gas 2 Rates of Evaporation are a function of Amount of water already in atmosphere Air temperature warm masses hold more moisture because as air temperatures rise the heightened molecular activity of warmer air fosters higher vaporization Water temperatures warmer water has more agitated molecular activity and heightens waters ability to vaporize Winds stirs up saturated zone dispersing water vapor allowing for more evaporation to take place Cloudiness decreased rate absorb EMR required for evaporation 3 Limits to Evaporation Vapor Pressure The pressure exerted by water vapor in the air When there are enough water vapor molecules in air to exert max vapor pressure at any given temp the air is saturated Evapotranspiration The transformation of water from a liquid to a gas by the combined processes of 1 Evaporation of water from the continents soil 2 Transpiration of water form plant leaves The Process Plants absorb water form the soil through their roots Photosynthesis CO2 H2O Carbohydrates O2 Excess water taken in is released or transpired through plant leaves Rates higher during sunlight hours Measuring Moisture in the Atmosphere The moisture held in the atmosphere in the form of water vapor is referred to as humidity and measured in the following ways Absolute Humidity Amount of water vapor in a given volume of air Expressed in grams of vapor per cubic meter of air As volume of air changes so does humidity Affected by temperature warm air capable of higher absolute humidity Direct indication of potential precipitation Specific Humidity Mass of water vapor in a given mass of air Expressed in grams of vapor per kilogram of air Changes only as quantity of water vapor changes not affected by volume Useful in studying air masses Relative Humidity Ratio between the water vapor in the air and the amount the air could hold if it were saturated Expressed as a percentage Relative humidity water vapor capacity Example if a parcel of air at 40 degrees C has a relative humidity of 50 it has 50 of the moisture it could hold if it were saturated A change in temperature will bring about a change in relative humidity Dew Point The temperature at which saturation occurs 100 humidity and condensation begins Sensible Temperature Temperature sensed by a person s body The temperature at which saturation occurs 100 humidity and condensation begins Varies with the moisture content of air High Dew point indicate high moisture content in the air