Warm up 9/16/15 How do old school (analog) thermometers (temperature measurer) and barometers (pressure measurer) REALLY work?

Brought to you by… Pressure in the atmosphere caused by the sun!

Now… What is Weather?

Weather Weather: the condition of the atmosphere at a specific time and place Weather is brought to you by – The atmosphere – The sun!

Up first… a review of the water cycle

Crazy fact…. Remember, the atmosphere is 99% oxygen and nitrogen. 1% is everything else. Within that 1% is water. Water makes up less than 1% of our atmosphere yet it is the water cycle = weather = Life =  happy face

The Water Cycle Don’t go crazy with this one... It’s just a review

Terms to be familiar with… Condensation = gas  liquid Evaporation = liquid  gas Run-off = way water gets back to earth’s surface Precipitation = way water is transported on earth’s surface

Vocab Time Time for Vocab overload – Temperature – Atmospheric Pressure – Humidity – Relative Humidity – Dew Point There is no better way to do this just go for it. But you need these to understand other stuff

Temperature (again) Temperature: the actual speed that particles are moving. We measure the speed that they are moving with a thermometer.

Isotherms ISOTHERMS: on temperature maps, these are lines drawn to connect points of equal temperature. Because it is so useful to us, we make maps showing us the temperature of different locations. These maps look like topo maps because they have familiar looking curving lines.

RULES FOR DRAWING ISOTHERMS: Must be pretty - smooth flowing lines, no corners or sharp angles No touching and no crossing No dead ends

Adding pretty colors to isotherms

Atmospheric Pressure (again) Atmospheric Pressure: the weight of the atmosphere or force of air on something. We measure with a barometer.

What is Standard Pressure? “Base” pressure is mb Approximately everything more than mb is HIGH pressure Approximately everything less than mb is LOW pressure This value is taken at sea level so it “mean sea level pressure” must be differentiated from “actual pressure”

Isobars ISOBARS: lines that connect points with equal pressure. Isobars work in the exact same way as isotherms, and contour lines, so at this point we should be able to construct an isobar map easily. Because air pressure can tell us so much about how the weather is likely to change, meteorologists track air pressure data closely.

Isobar map example

Humidity Humidity: The amount of water vapor in the air

Humidity and Temperature Humidity changes with the temperature of the air When the air is hot, it has a higher CAPACITY meaning it can hold more moisture because the faster molecules are more likely to be in the gas phase When the air is cold, it has a lower CAPACITY meaning it holds less moisture.

Amount of water air can hold at certain temperatures

Relative Humidity Relative humidity: the ratio of the amount of water in the air (the humidity) to the amount it can hold (read from a table) as a percent Relative humidity measures how FULL of water the air is.

If you don’t calculate Relative Humidity with the formula then you can measure it with a tool and table Relative humidity is measured using a PSYCHROMETER. (the tool) + chart Inside the there are 2 thermometers. 1 thermometer has a cloth (wet bulb) and the other doesn’t (dry bulb). You read both thermometers and the difference between the temperature helps give you the calculation (just look at a table). The larger the difference between the 2 readings, the lower the humidity.

Psychrometer calculating Relative Humidity

Putting Temperature and Relative humidity together we get the heat index or “feels like” temperature

Dew Point Dew Point is temperature at which condensation begins. As soon as the air temperature reaches the dew point water vapor will begin to condense

Dew point measuring Tool: We measure the dew point temperature with a psychrometer + chart in the exact same way as we measure relative humidity. The only difference is we use a different chart.

Dew Point Chart

Relationships between vocab terms All of these measurements are important to track because they allow for predictions about the probability of different types of weather we compare them to one another Ex: dew point and relative humidity

Relationships Example: Temperature and Dew Point When the air temperature and dew point are close together that means: – Relative Humidity is High – Condensation is occurring – It is likely to rain When the air temperature and dew point are far apart that means: – Relative Humidity is Low – Evaporation is occurring – It is likely clear and sunny

It’s raining here… lines are close No rain… far apart

Confused yet? Me too… Hopefully this helps (some of it anyway…) 9JGe5yU-Us 9JGe5yU-Us (youtube search: “humidity 101”)

Clouds!!! Clouds are classified based on height and shape. There are lots… Here’s how they form

Precipitation There are 4 main types of precipitation… – Rain- warm – Sleet- cold – Snow- coldest – Hail - forms in a cloud

Precipitation

Weather Stations You can summarize all these things with one picture we call station symbols Each station symbol gives the – Temperature – Dew point – Cloud cover – Wind direction – Wind speed – Air pressure – Current weather (if it is precipitating and type) 1010

Example: What are…. – Temperature: ___________ – Dew point: ____________ – Cloud cover : _________ – Wind direction: _________ – Wind speed:_________ – Air pressure: _________ – Current weather: _________ 1021

Dew pt calculation

Relative humidity calculation

FYI: how to measure relative humidity The tool for relative humidity is called a psychrometer Inside the psychrometer are 2 thermometers. 1 thermometer has a cloth (wet bulb) and the other doesn’t (dry bulb). You read both thermometers and the difference between the temperature helps give you the calculation (just look at a table). The larger the difference between the 2 readings, the lower the humidity.

Saturated (full of water) Air Water vapor is added to the atmosphere through evaporation. At some point, however the air becomes SATURATED or full of water. At this point, the relative humidity is 100%, the wet bulb and dry bulb are the same, evaporation stops, and water vapor must come out of the air. Under these conditions CONDENSATION occurs

A psychrometer is a device made from 2 different thermometers. One of these thermometers is completely normal, and simply measures the air temperature. This one is called the DRY BULB. The other thermometer has a damp cloth tied around it. This one is called the Wet Bulb. Because evaporation occurs on the wet bulb, the wet bulb value is always lower than the dry bulb