# Presentation: 559441

## Relative Humidity Protocol

## Goals for the Training Session

- Provide an inquiry context for the data collection and science content
- Provide accurate science content
- Review procedures for data collection
- Review data entry and analysis
- Discuss classroom implementation ideas
- Collect feedback from participants

**Notes:**
These are the goals for the Relative Humidity Protocol training session.

Photo shows a GLOBE Trainer reading the wet bulb thermometer of a sling psychrometer (Fort Collins, Colorado, May 2004).

## Inquiry Context

- Are relative humidity and cloud measurements related?
- At what time of the day will relative humidity normally be at a maximum? At a minimum?
- How is dew point temperature related to relative humidity?

- © National Center for Atmospheric Research

**Notes:**
Picture shows fog. Photo taken by the National Center for Atmospheric Research.

## Local Inquiry Example

**Notes:**
Students can generate local inquiry questions to create a context for data collection to answer the question. Local inquiry topics can be connected or scaled to provide a local to global perspective on environmental research.

Please generate a local example that teachers and students can relate to.
Examples:
-How are your relative humidity observations related to air temperature?
-Can you find other GLOBE sites at your latitude which are closer to or further from large bodies of water?  Do you see any systematic differences in relative humidity between your location and the others?
-Does relative humidity affect any non-atmospheric parts of your local environment?  How?
-Are your relative humidity and phenology measurements related?

## Why do GLOBE scientists research relative humidity?

- Provide a denser network of observations than is available using only official weather stations
- For investigating the relationship between relative humidity and land cover
- Augment data needed for regional forecasts and climate records

- Photo taken by Caspar Amman
- © University Corporation for Atmospheric Research

**Notes:**
Student-collected measurements in the Precipitation Protocols are helpful to scientists in the following ways.
To provide a denser network of observations than is available using only official weather stations
For investigating the relationship between relative humidity and land cover (e.g., urban heat islands, microclimates)
To augment data needed for regional forecasts and climate records in areas of the world where there are few official weather stations

Photo shows the Atacama Desert of northern Chile.  Photo taken by Caspar Amman.  Copyright University Corporation for Atmospheric Research.

## Science Content: What is Relative Humidity?

- amount of water vapor in the air
- amount of water vapor in the air
- at saturation

- RH =

**When Air is Saturated:**
- It contains the maximum amount of water vapor at the current air temperature and pressure.
- Water droplets or ice particles begin to form.
- RH = 100%

**Notes:**
Humidity is the amount of water vapor present in the atmosphere.
Relative humidity is a measure of the amount of water vapor in an air sample relative to its value if the air were saturated.
For example, at 20 degrees C 16 gm water vapor/kg air is required for 100% relative humidity. Thus, if there are 8 grams of water vapor for each kilogram of air, the relative humidity would be 50%.
Air is said to be saturated when it reaches the maximum amount of water vapor possible at its current temperature and air pressure (more water vapor is present in warm air than cool air).

## Science Content

- Relative humidity is important because it...

- Influences rates of evaporation and evapotranspiration
- Influences the height of cumulus clouds
- Determines how cool it will get before dew forms (and the temperature at which dew forms is often the minimum temperature)
- Is a key element of local climate.

**Notes:**
Evaporation is more rapid in dry air (and at warmer temperatures).
Evapotranspiration is the release of water vapor from photosynthesizing plants.  Relative humidity tends to be higher over actively photosynthesizing plants than over dormant plants.

The base of cumulus clouds tends to be lower when the relative humidity is higher.  When there is fog, the relative humidity is close to 100%.  In dry climates, cumulus clouds have higher bases.  

Once the temperature cools enough, dew forms.  As the ground and air continue to loose heat, it is compensated for by the latent heat released when water condenses.  (We experience the opposite effect when we get out of a shower or swimming pool – the water evaporates and cools our skin).  Thus, on humid nights, it doesn’t cool much, but it can cool a lot when it is dry.  That is why the temperature at night drops much more in continental climates than in marine climates (close to the ocean).

Rain is more likely when the relative humidity is higher in the middle of the day.
Since relative humidity influences so many things – night time cooling, cloud formation, etc., it clearly affects the local climate.

## Instruments: Digital Hygrometer

- Ceramic and metallic compounds measure electrical resistance
- Directly reads relative humidity
- Works below freezing
- Needs 30 minutes                        outside before reading
- Must be kept indoors and/or                                   in a dry container
- Ruined by condensation

**Notes:**
Digital hygrometers use ceramic and metallic compounds to measure electrical resistance
Directly reads relative humidity
Works below freezing
Needs at least 30 minutes to adjust to outside conditions
Can be ruined by condensation (it is not weatherproof)
Must be kept indoors and/or in a dry container (e.g., a can with rice and a tight lid) if indoors is not climate controlled

Photo shows a digital hygrometer in an instrument shelter. (Fort Collins, Colorado, May 2004)

## Instruments: Sling Psychrometer

- Relative humidity is calculated using the temperatures of the wet bulb and dry bulb thermometers.

- Dry bulb thermometer measures air temperature

- Wet bulb thermometer has a wet wick that measures air cooled by evaporation

**Notes:**
Use two thermometers that are whirled by hand. Each thermometer should also be calibrated against the calibration thermometer before use and once every three months.

The wet bulb thermometer has a wet wick attached that is cooled by evaporation when the device is whirled.  
The amount of evaporation depends on the relative humidity and the air temperature 
Relative humidity is calculated using the temperatures of the wet bulb and dry bulb thermometers

**The sling psychrometer doesn’t work well at temperatures below freezing.

## The Measurements

**Digital Hygrometer**
- Relative humidity reading
- Current air temperature
**Sling Psychrometer**
- Dry bulb temperature
- Wet bulb temperature
- Current air temperature

**Notes:**
You can use either the digital hygrometer or the sling psychrometer to take the relative humidity readings.  In both cases, you will also need to take the current air temperature reading.  However, it is recommended to use the digital hygrometer in locations where the temperature frequently goes below freezing.

## Collecting Data: Field/Lab Guides & Data Sheets

**Field/Lab Guides:**
- Use _**one**_ of the following:
- Digital Hygrometer Field Guide
- Sling Psychrometer Field Guide
- And _**one**_ of the following:
- Digital Multi-Day Max/Min/Current Temperature Protocol Field Guide
- Maximum, Minimum, and Current Temperature Protocol Field Guide
**Data Sheets:**
- Use _**one**_ of the following:
- Integrated 1-Day Data Sheet
- Integrated 7-Day Data Sheet
- Ozone Data Sheet

**Notes:**
Field/Lab Guides: All Field Guides are located in the Atmosphere Investigation of the Teacher’s Guide.  The respective chapter and pages numbers are included below:
Use one of the following:
-Digital Hygrometer Field Guide (Relative Humidity Protocol – 6)
-Sling Psychrometer Field Guide (Relative Humidity Protocol – 7)
And one of the following:
-Digital Multi-Day Max/Min/Current Temperature Protocol Field Guide (Multi-Day Maximum, Minimum, and Current Air and Soil Temperature Protocol – 10)
-Maximum, Minimum, and Current Temperature Protocol Field Guide (Maximum, Minimum, and Current Temperature Protocol – 7)
Data sheets: The data sheets are located in the Appendix of the Atmosphere Investigation of the print Teacher’s Guide or they can be downloaded from the Teacher’s Guide link on the GLOBE Web site at any time.
-Integrated 1-Day Data Sheet (Appendix – 7,8)
-Integrated 7-Day Data Sheet (Appendix – 9,10,11)
-Ozone Data Sheet (Appendix - 23)

## Collecting Data: Protocol

**Digital Hydrometer**
- Place outside in instrument shelter for 30 minutes
- Take relative humidity reading
- When there is rain or fog 100% is reported without taking measurement

**Sling Psychrometer**
- Stand in shade near instrument shelter
- Keep away from body
- Wait 3 minutes, take dry bulb reading
- Whirl sling psychrometer for 3 minutes, take wet bulb reading

**Notes:**
**At this point give the participants the field guides and data collection sheets, go outside, and let them practice the measurements. 

It is actually possible to have relative humidities of less than 100 per cent when big, cool, raindrops are falling.  However, it is extremely difficult to measure relative humidity when it is raining, and 100% is a close estimate. Trying to measure relative humidity when it is raining will damage the instrument.  

## Enter Data on the GLOBE Web Site

- Step 1: Confirm that the atmospheric 	  	      study site definition is completed
- Step 2: Select “Integrated 1-Day, 7-Day, or Surface Ozone” from the atmosphere data entry menu
- Step 3: Enter date/UT time/select site
- Step 4: Enter collected data
- Step 5: Confirm data entries on verification page

**Notes:**
**At this point, direct the participants to the GLOBE training data entry site and have them enter the data from their data collection sheets. Note: You will need to have a site definition already established or complete the Instrument Construction, Site Selection, and Set-Up training and define an atmosphere study site prior to entering the Relative Humidity data.
STEP 1: Be sure that you have completed an atmospheric study site definition.
STEP 2: Select one of the three data entry pages from the choices listed in the menu to enter relative humidity data.
STEP 3: A valid date and UT time and select the site in order to enter the data. 
STEP 4: Enter the data collected from the data sheet.
STEP 5: Confirm that the data entries are correct on the verification page.
You may click the enter more data button or return to the data entry home page or the main GLOBE home page when finished.

Email data entry is also available.  Directions can be found on the GLOBE Web site under Data Entry.

## Looking at the Data

**Notes:**
***Data Analysis suggestion and explanation by Matt Rogers (rogers@atmos.colostate.edu)***
Something interesting to look at is the relationship between relative humidity and maximum temperature.  Usually, days that are more humid don’t get as hot (although they feel hotter) as days that are not humid.  Water vapor plays a large role in air temperature – moister air tends to be more temperate, while drier air can experience more extreme swings in temperature.  In this plot, there’s a cooler day around the 15th with higher relative humidity (although this could be due to passage of a cold front, as well.)  Another way to show this would be to compare schools from different cities at the same latitude (say, Santa Fe, NM and Little Rock, AR) – the drier school in NM would have higher max temps than the more humid school in Arkansas. 

Refer to the “Looking at Data” section of this protocol in the Teacher’s Guide for a data analysis activity.

## Classroom Implementation

- Inquiry
- Curriculum/Standards Alignment
- Assessment
- Classroom Management

**Notes:**
Have participants break into groups and discuss one or more of the above bullet items, as time allows.

## Getting Started

- The GLOBE Web site has information
- _[http://www.globe.gov](http://www.globe.gov/)_
- GLOBE Help Desk or your Country Coordinator can support you as you get started.
- Get your students involved doing real science!