Aim : What is relative humidity? Do Now : Answer the following in your notebooks;

Aim: What is relative humidity? Do Now: Answer the following in your notebooks; • What do you think of when you hear it is humid out? • Explain what type of pressure is outside and how you know. • Since it is windy here, what does that tell you about the pressure around RVC?

What do you think of when you hear it is humid out? • Explain what type of pressure is outside and how you know. • Since it is windy here, what does that tell you about the pressure around RVC? it’s wet, its hot, it’s uncomfortable There is low pressure outside because it is lousy weather (wet, windy, cloudy) The surrounding areas must have different (higher) pressures; wind blows from High --> Low pressure

I. Vocabulary a) Humidity – is a measure of how much water vapor is in the air. b) Parcel– a section or part of something. A parcel of air is a section of the atmosphere we are discussing.

Which temperature air can hold the most water vapor? - Warmer air can hold more water vapor than cooler air. WHY? Warm air - Warm air expands and has more space to hold water vapor Cold air

II.Relative Humidity (RH) : describes “how full” the air is with water vapor (expressed as a percent (%)). - compares the size of the air to the amount of water in the air.

What caused this parcel of air to change it’s size (expand)? What happens to the RH as the air temperature changes? - heat causes air to expand and allows it hold more water vapor.

When saturated, which temperature air will hold more water vapor? - Saturationthe air is 100% filled with water vapor. Warm air Cold air WHY? Warm air is more spread out and can hold more water vapor They have the same RH = 100% Which parcel of air has a higher relative humidity?

- When the Relative humidity = 100%, the air is Saturatedand Condensation can occur (makes clouds and rain)

Take the worksheet from the back top bin and work on the side the says What is Humidity? only

III. Changing the Relative Humidity a. Water vapor enters or leaves the air. (evaporation or condensation) b. The temperature changes. (changes the size of the air) How can you change the Relative Humidity of the air? (Think, what is the definition of RH?)

IV. Dew Point Temperature - always lower than the air temperature - indicates when the air will be saturated with water vapor. (RH = 100%) Example: Below the parcel of air has a dew point temperature of 750F. What will this dew point temperature do to the air? RH = 50% Air Temp. = 870F RH = 100% Air Temp. = 750F

- As air temperature gets closer to the dew point temperature… • there is better chance for precipitation. 1) At what time is the RH the highest? 2) At what time is RH the lowest? 3) When is the greatest chance of rain? 6am 3pm 6am

V. Measuring DP and RH: - Sling Psychrometermeasure the RH and DP. • uses a dry bulb temperature and wet bulb temperature. • The wet bulb temperature is always lower. Why would the wet bulb thermometer always at a lower temperature? What is the water doing?

Calculate the difference between dry and wet bulb temps. This is called the wet bulb depression. • Use ESRT p.12 Example: A student measure the temperature of the air using a sling psychrometer and found that the Dry Bulb Temp. = 240C and the Wet Bulb Temp. = 200C. What is the wet bulb depression temperature? Relative humidity? Dew Point?

When trying to determine Relative Humidity and Dew Point, create a list of the information you need, and the information you have to make solving the problem easier. Example: Dry bulb = 240C Wet Bulb = 200C Depression = ? RH = ? DP = ? 40C 18 C 69% • Subtract the wet bulb from the dry bulb value. - Use the ESRT page 12 charts to look up the Dew Point Temperature and the Relative Humidity.

Work on the other side of the worksheet you already have

Aim : What is relative humidity? Do Now : Answer the following in your notebooks;