Introduction

What is Precipitable Water?

Precipitable water is the amount of condensed water vapor to be found in a vertical column of air, with a base of 1 meter-squared, that extends from the surface of the Earth to the top of the atmosphere.


Figure 1: Schematic illustrating the concept of precipitable water. The left column contains air and water vapour, the right column contains dry air and condensed water vapour on the bottom of the column [1].

Precipitable water is important because:

• Energy is transferred from the surface to the atmosphere via water vapor, and is released as latent heat. Precipitable water helps us determine the amount of energy in the atmosphere.
• Weather forecasting models can use precipitable water data to determine the likelihood of storms, hail, and other major meteorological events.
• The relationship between air temperature and the amount of water vapor is linear. Therefore, precipitable water measurements can be used to determine temperature increases at higher altitudes.

Goal

The goal of this project is to determine the correlation between zenith sky temperature and precipitable water. This experiment is based off of a similar study conducted by Mims et al [2]. We endeavor to develop a methodology and data source that is more rigorous, more accessible, and more easily repeatable across a variety of climate zones.

Intstrumentation

This experiment used three infrared sensors (from left to right):

1. 1610 TE
2. FLIR i3
3. AMES

The purpose of these sensors is to measure the thermal energy of a given area in the atmosphere. The area is determined by the Distance to Spot ratio.

When using the model for your analysis, take the time to fully complete the _pmat.yml file with the appropriate information. This will assure that the data properly corresponds to the labels of the sensors. If there is an entry that you are unable to fill, please use NA as a filler. More information regarding the different columns of the _pmat.yml will be discussed in the Working with data and PMAT section of the Official PMAT Documentation.

What is PMAT?

The Precipitable-water Model Analysis Tool (PMAT) is a computational utility that is used to analyze the data collected from this project to understand the relationship between the zenith sky temperature and precipitable water in the atmosphere. For more information regarding PMAT, visit the Official Documentation Page.

Methodology

Setting Guidelines

1	Determine the scope of project and reporting frequency
2	Identify the closest MesoWest and wyoming sites to your area.
3	Determine daily measurement site and time, to ensure consistent measurements happen.
4	Decide on different infrared thermometers to take measurements with

Experimental Procedure

1	At the same location and time take both ground and zenith sky temperature readings with the thermometers (Ensure that the sun is not directly above when taking your readings)
2	Record the ground and zenith sky temperature for each thermometer (If the zenith sky reading is obstructed by cloud cover, record the condition as overcast. Otherwise record the condition as clear sky) (Do not leave blanks in your dataset. Any value that is not available needs to be marked as -Inf or NaN)
3	Retrieve precipitable water readings and add them to your dataset

Data Analysis

To complete the data analysis look at the procedures for PMAT deployment and follow the steps that best fit your needs.

Contributing to the Research

If you would like to contribute to this project, visit our contribution page.

Next Steps

The future development of this project with regards to the data collection include a machine learning approach to determining weather condition (Clear sky/Overcast). We are also in the process of developing a method of automating the temperature measurement process using an Arduino-Raspberry Pi network.

Resources

• University of Wyoming Sounding Data
• University of Utah MesoWest

References

[1] Mária, P. (n.d.). Product Tutorial on TPW Content Products.

[2] Forrest M. Mims, Lin Hardtung Chambers, and David R. Brooks. Measuring total column water vapor by pointing an infrared thermometer at the sky.Bulletin of the American Meteorological Society, 92(10):1311-1320, 2011.