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# Introduction to weather

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### Introduction to weather

1. 1. Earth Science Weather I. Introduction to weather a. Weather i. Is the short term condition of the atmosphere at any location ii. It is made up of the connection and relationship of 1. Temperature 2. Humidity 3. Air pressure 4. Wind II. Temperature Introduction a. at any given place temperature is connected to the heat energy present in the atmosphere at that location b. Solar radiation is the amount and how long the sun is on a particular location and how strong it is. c. Therefore anything that changes solar radiation will also change the air temperature d. What are factors that can effects solar radiation? i. The following are factors that can change the amount of solar radiation a place has 1. The angle that solar radiation hits the Earth 2. this changes throughout the day because of the Earth rotation 3. Solar radiation is only present during the day 4. similar changes also happen when the Earth moves around the sun a. we call these slower changes seasons 5. number of hours of solar radiation during the day 6. the reflection 1
2. 2. Earth Science Weather 7. refraction 8. absorption of solar radiation a. for example clouds block and absorb the amount and intensity of the sun 9. and the type of surface (ex: water and land) e. How do we measure air temperature? i. Temperature is measured with thermometers 1. Works on a simple principle 2. Matter expands when heated and contracts as it cools. ii. There are many scales of measuring temperature that are named after the people who made them up 1. Celsius 2. Fahrenheit 3. Kelvin iii. Here in America we use Fahrenheit the rest of the world uses Celsius iv. Meteorologist ( people who study weather ) use a thermograph as a thermometer 2
3. 3. Earth Science Weather III. Air Pressure a. Introduction i. Air is a mixture of different gases ii. Gas consists (made up of) many different tiny molecules that move around rapidly and are far apart from each other. 1. They are kept contained either by a container or in the case of the atmospheres by the Earth’s Gravity iii. Gases put pressure on the surfaces that they are in contact with. iv. In the case of air pressure this pressure is due to the gas particles bumping into the surface v. Since they move rapidly in all direction they balance out this pressure in all directions b. How does air pressure help us forecast weather i. You cant sense air pressure like you can with temperature ii. Nor can you forecast the weather based on the air pressure in a location iii. BUT since we have isoclines of the air pressure, we can study the changes of the air pressure and the different masses and temperatures that come with it. 1. Rising pressure usually means fair weather 2. Low Pressure usually means an approach of a storm c. How is air pressure measured? i. We use a barometer to measure air pressure. 3
4. 4. Earth Science Weather d. there are two common barometers used 1. Mercury Barometer 2. Aneroid Barometer •air pressure forces liquid mercury •aneroid means no liquid up a tube •it is a can with a spring scale on it •the more pressure the higher the •the amount of pressure on the sides mercury level will be of the can will either push down or •we usually name the number with loosen the spring scale inches or millimeters attached to the number e. air pressure is measured based on units of force per a unit area 1. atmosphere (atm) is the average air pressure at sea level Homework 4
5. 5. Earth Science Weather Based on the Lesson on Temperature and air pressure Please identify the following terms 1. weather- __________________________________________________________ _________________________________________________________________ _ 2. Temperature - ______________________________________________________ _________________________________________________________________ _ 3. Solar radiation - ___________________________________________________ _________________________________________________________________ 4. thermometer - ______________________________________________________ _________________________________________________________________ _ 5. Seasons -_________________________________________________________ _________________________________________________________________ 6. Air pressure - ______________________________________________________ _________________________________________________________________ _ 7. Barometer- ________________________________________________________ 5
6. 6. Earth Science Weather _________________________________________________________________ _ Please answer the following questions. 1. How does solar radiation affect temperature? a. __________________________________________________________ __________________________________________________________ _______________________________________________________ 2. Name 5 things that can affect solar radiation? a. __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ ____________________________________________________ 3. How do we measure temperature? How do scientist measures air temperature? a. ________________________________________________________ 4. What are the three scales of measuring temperature? Which one do we use? a. __________________________________________________________ __________________________________________________________ _______________________________________________________ 5. How does gravity help air pressure? a. __________________________________________________________ ________________________________________________________ 6. How does Air pressure help us forecast the weather? 6
7. 7. Earth Science Weather a. __________________________________________________________ __________________________________________________________ _______________________________________________________ 7. What are the differences between the aneroid and mercury barometers? IV. Air Movements a. The reason why air circulates is because of density differences b. Air Currents i. Air currents are the rising and sinking vertical movements of the air ii. When these air currents sink and they reach the earth’s surface it does spread out horizontally. When the rising air expands it also spreads out horizontally. c. Wind i. When these air currents expand horizontally it forms wind. 1. Wind is described by a. Speed b. Direction ii. Speed 1. is measured by an instrument called an Anemometer. a. An Anemometer is 3-4 cups mounted on an axis that is attached to a compass. b. The wind moves the cups causing the axis to spin. 7
8. 8. Earth Science Weather c. The speed of the axis’s movements depends on the speed of the wind. d. Wind Speed is measured by knots i. 1 knot= 1.15 miles an hour iii. Wind Direction 1. Measured by a wind vane a. A wind vane is a pointer on an axis that is also attached to a compass b. The tail of the pointer is larger than the tip i. This makes sure more pressure is put on the tail ii. Therefore it will point to the direction that the wind is coming. 8
9. 9. Earth Science Weather V. Humidity a. Humidity i. Is the amount of Moisture in the air ii. IT IS NOT a liquid water in the air but rather it is water vapor (gas) 1. water vapor is a colorless, odorless gas that enters the atmosphere when liquid water evaporates or ice sublimes ( changes straight from solid to gas) iii. Humidity is a very important weather factor because the water vapor in the air is what condenses to form 1. cloud 2. fogs 3. precipitation b. The changing of water i. Water molecules are always changing from the three forms of matter 1. solid 2. liquid 3. gas ii. So therefore it looks like this 9
10. 10. Earth Science Weather Ice Water Water Vapor c. How does water enter the atmosphere i. Most water enters the atmosphere from the form of liquid to gas 1. called evaporation ii. or ice to gas 1. called sublimation d. How does water leave the atmosphere? i. Condensation 1. Water forming and leaving the atmosphere (We will talk later why water falls) ii. Deposition 1. Is when the vapor form into solid crystal without turning into water first e. This constant flow of water molecules throughout these phrases results in the change of humidity f. The greatest amount of change in water molecules occurs between the atmosphere and hydrosphere (water) i. The molecule of water from the hydrosphere gain energy from sunlight and surroundings may become energetic enough to escape the liquid phase and turn into water vapor ii. When water vapor molecule come in contact with the hydrosphere they sometimes get attached and stay there 10
11. 11. Earth Science Weather iii. it is a two way street. g. Evaporation i. Is when the molecules get enough energy and form into water vapor in the atmosphere 1. at higher temperatures molecules have more energy so more molecules will have the energy to escape and form into vapor HIGHER TEMP MORE EVAPORATE h. Condensation i. Is when the water vapor molecules form a liquid and attach themselves onto the surface ii. This depends on how densely populated the molecules are. The more populated in a small area the more will attach themselves onto the surface 1. like being squeezed out of an elevator i. Net Evaporation and Net Condensation i. Net evaporation 1. is when there is more molecules leaving the surface than there are attaching to the surface ii. Net condensation 1. is when there is more molecules leaving the atmosphere and attaching to the surface than those leaving the surface iii. They go in a circle though 1. if there is a net evaporation the more water vapor there is in the air which means the denser it will get and more vapor gets pushed out and stuck to the surface 11
12. 12. Earth Science Weather 2. eventually a point is reached where their is an equilibrium 3. If the temperature drops suddenly then the water vapor will be more then the equilibrium j. Relative Humidity /Absolute humidity i. The amount of water vapor in the air is usually referred to absolute or relative humidity ii. Absolute Humidity – is the amount of vapor found 1 cubic meter of the air. 1. since it is very hard to isolate the water vapor in the air in order to measure it absolute humidity is very rarely measured iii. Relative humidity 1. is the ratio of water vapor bow present in the atmosphere to the water vapor present when evaporation and condensation are equal at that temperature X 100 Water vapor in atmosphere Relative humidity = ------------------------------------------------------ X100 Water vapor in atmosphere at equilibrium 2. relative humidity is a way to of comparing the flows of water molecules leaving and arriving at a surface. 12
13. 13. Earth Science Weather 3. it is useful in predicting how the air will feel to a person AND whether evaporation or condensation would more likely occur. Point of information 1. Relative humidity 20% means that the air only has 20% of the water vapor it would have during equilibrium 2. relative humidity of 100% means that the air contains 100% of the water vapor it has during equilibrium 4. The higher the relative humidity the (stickier) the air will feel. 5. If the relative humidity is 100% it does not mean that the air is 100% water vapor it still has oxygen and nitrogen etc…….. 6. High relative humidity a. Means that the WV in the air is close to it’s equilibrium amount b. A decrease in temperature (will also decrease the temperature amount needed for condensation) will decrease equilibrium amount needed for condensation which makes fog, clouds, or precipitation 7. Dew Point a. This leads us to dew point b. Dew point is the temperature at which water vapor in the air will begin to condense into liquid water 13
14. 14. Earth Science Weather c. THIS IS THE TEMPRATURE AT WHICH THE AMOUNT OF WATE VAPOR IN THE AIR EQUALS THE AMOUNT OF EQUALIBRUIM FOR THAT TEMP. 8. How is Humidity measured? a. There are two different tools used to measure humidity i. Hygrometer ii. Psychrometer b. Hygrometer i. Consists of strands of human hair attached to a pointer ii. Human hair grows slightly as humidity increases 1. and shrinks when it decreases iii. The pointer changes position based on the length of the hair c. Psychrometer i. Is made of two thermometers 1. Dry bulb a. The bulb is kept dry 2. Wet bulb – the bulb is kept wet by a covered cloth wick soaked in water a. Evaporation from the wet wick causes cooling because the fastest 14
15. 15. Earth Science Weather molecules in liquid water are the ones that have enough energy to escape b. The slower molecules have a lower average energy. c. Therefore the liquid temperature decreases due to the loss of energy. 3. This cooling effect is KEY to measuring relative humidity 4. The lower the relative humidity the more water can evaporate from the wet bulb and the more the thermometer is cooled. 5. The Dry Bulb Temp. remains unchanged. 6. Therefore the difference between the dry bulb and wet bulb temperature is directly related to the relative humidity of the air. d. How do we figure out the relative humidity? 15
16. 16. Earth Science Weather i. You subtract the dry bulb e from the wet bulb temp ii. Find in the table where the dry bulb temp (right side) and the difference temp # meet iii. That number is your relative humidity percent e. How do I figure out the dew point in the air? i. The difference between the wet and dry bulb is also directly related to dew point. ii. The higher the relative humidity the closer the air is being filled to capacity. iii. Cooling air decreases the capacity to hold water iv. So we will use a different table 1. you will figure out the difference between Wet and dry 2. You will then see where it meets with the dry bulb temperature 3. That number at the intersection is the dew point in degrees of C. 16
17. 17. Earth Science Weather 17