How to calculate sensible heat flux

Written by charles alex miller
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How to calculate sensible heat flux
Sensible heat flux allows energy to transferred between the atmosphere and water. (ocean image by Yulia Volodina from Fotolia.com)

The sensible heat flux is a phenomenon that allows the Earth to exchange heat between a body of water, most often the ocean, and the adjacent atmosphere. Sensible heat flux can be calculated using an atmospheric model or by using a heat flux formula. The heat flux formula is fairly simple and can be solved using basic algebra. It is calculated using a number of variables including air density, transfer coefficients, heat capacity, air and water temperatures and wind speed.

Skill level:
Easy

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Things you need

  • Access to atmospheric data from government agencies such as NOAA

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Instructions

  1. 1

    Obtain data from a government or university lab or agency. Agencies such as the National Oceanic and Atmospheric Administration, or NOAA, use satellites to obtain sea surface temperatures. This process is incredibly difficult and expensive, so more often than not, data is obtained using models. Other variables are often obtained using these methods, measuring onsite from a boat or using averages.

  2. 2

    Write down the following formula:

    Q_s = ρ *C_h * C_p * (T_w -- T_a) * U

    This is the basic formula to calculate heat flux. As you can see, there are many unique variables in this equation. Each is equally important in solving this equation. "ρ," also known as the Greek letter rho, represents atmospheric density. In atmospheric science, rho is always in kilograms per cubic square meter. If you have data in another unit, you will have to convert it. "C_h" is a variable for the transfer coefficients of the given area. This number typically ranges between 1.1E-3 and 0.8E-3. There is no unit for this number, because it is merely a coefficient. Atmospheres with higher levels of vertical mixing typically have higher transfer coefficients, while less active atmospheres have lower transfer coefficient values. "C_p" is a representation of the specific heat or heat capacity of the air sample. This variable is in Joules/kilogramKelvin. On average, the specific heat of air is around 1,006 J/kgK. "T_w" and "T_a" are variables for temperature. They are the temperatures of the sample water and air respectively. To achieve consistency with other variables, these values need to be in Kelvin. If you have measurements in Celsius, merely add 273 to your Celsius value to convert it to Kelvin. Finally, "U" is a representation for speed of wind above the water. Average wind speeds over Earth oceans are around 7.4 meters per second.

  3. 3

    Solve for "Q_s" using basic algebra and the proper order of operations. The resulting value is a representation of the amount of energy given over a two-dimensional surface. It will be in watts per square meter, designated W/m^2. Properly calculated formulas that use data from sophisticated and accurate instruments have an error of up to +/- 15 W/m^2.

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