Actual Vapour Pressure Given Evaporation Loss Per Month Calculator

Formula Used:

\[ v = V - \frac{E_m}{C \times \left(1 + \frac{u}{16}\right)} \]

Maximum Vapour Pressure:

cm Hg

Evaporation Loss per Month:

Meyer's Constant:

Mean Wind Velocity:

m/s

Actual Vapour Pressure:

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1. What is Actual Vapour Pressure?

Actual Vapour Pressure refers to the pressure exerted by the water vapour present in the air, reflecting the current humidity and temperature, typically measured in cm Hg or kPa. It represents the real amount of water vapor in the atmosphere at a given moment.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ v = V - \frac{E_m}{C \times \left(1 + \frac{u}{16}\right)} \]

Where:

\( v \) — Actual Vapour Pressure (cm Hg)
\( V \) — Maximum Vapour Pressure (cm Hg)
\( E_m \) — Evaporation Loss per Month (m)
\( C \) — Meyer's Constant (1.1 for deep water, 1.5 for shallow water)
\( u \) — Mean Wind Velocity (m/s)

Explanation: This formula calculates actual vapour pressure by subtracting the evaporation component from the maximum vapour pressure, accounting for wind velocity effects through Meyer's empirical relationship.

3. Importance of Actual Vapour Pressure Calculation

Details: Accurate vapour pressure calculation is crucial for meteorological studies, agricultural planning, evaporation rate estimation, and understanding atmospheric moisture content for various environmental and engineering applications.

4. Using the Calculator

Tips: Enter maximum vapour pressure in cm Hg, evaporation loss per month in meters, select appropriate Meyer's constant based on water depth, and mean wind velocity in m/s. All values must be valid positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the difference between actual and maximum vapour pressure?
A: Maximum vapour pressure is the saturation pressure at a given temperature, while actual vapour pressure represents the current water vapor content in the air, which is always less than or equal to the maximum.

Q2: How does wind velocity affect vapour pressure calculations?
A: Higher wind velocities increase evaporation rates, which affects the relationship between maximum and actual vapour pressure as accounted for in the formula.

Q3: When should I use different Meyer's constants?
A: Use 1.1 for deep water bodies (lakes, reservoirs) and 1.5 for shallow water (ponds, small water surfaces) as evaporation rates differ due to depth variations.

Q4: What are typical values for actual vapour pressure?
A: Actual vapour pressure typically ranges from 0-3 cm Hg depending on temperature and humidity, with higher values in warm, humid conditions and lower values in cold, dry conditions.

Q5: How accurate is this calculation method?
A: Meyer's formula provides a good empirical estimate for many practical applications, though for precise scientific measurements, more complex models incorporating additional atmospheric parameters may be required.