<p>It is reasonable to assume that air (atmosphere) acting as as a solution could become supersaturated with water vapor.  Supersaturation condition is where the air literally contains more water vapor than is needed to cause saturation. How common these conditions might be, I do not know.</p>

CC BY-SA 3.0
2016-08-16T20:36:04.533Z
2016-08-18T23:36:08.783Z
2016-08-18T23:36:08.783Z
Earth Science Expatriate
<p>The relative humidity is the ratio of the partial vapour pressure of air, to the equilibrium vapour pressure over pure water, at the same pressure - yes, it's slightly pressure dependent.But I would put an emphasis upon '<em>Equilibrium</em>'. In both physics and chemistry one can get all kinds of bizarre results under non-equilibrium conditions, and >100% RH is one of them. It is just a transient feature caused by rapid changes in temperature, pressure, or absolute vapour pressure, and as such it is not really a genuine meteorological observation. </p>

<p>Also, I advise caution when interpreting RH results. There is often a strong diurnal variation in RH, so if there is a met site taking only one reading a day, it could be unrepresentative of true average conditions. This is not so much a problem in advanced countries, where the measurements are (usually) reliably taken at set times. But it is often wildly misleading in developing countries where the observer may take a reading when/if he/she gets around to it, or maybe fakes the data altogether!</p>

CC BY-SA 3.0
2016-08-18T14:23:25.247Z
2016-08-18T14:23:25.247Z
Gordon Stanger
<p>I am processing a big meteorological data set, which is a global forcings dataset derived by other datasets and observations, and calculating relative humidity from qair,temperature, and pressure according to these formulas <a href="https://earthscience.stackexchange.com/questions/2360/how-do-i-convert-specific-humidity-to-relative-humidity">How do I convert specific humidity to relative humidity?</a></p>

<p>I am noticing that I have a lot of occurrences where RH is slightly higher than 100% and I am wondering if this makes sense or not considering this is air temp from 2m, I would expect that near surface RH over 100% is some errors in the data set.</p>

<p>*I am not a climatologist nor a meteorologist, I use this data to study plants, so I hope for a not too technical answer, thank you.</p>

CC BY-SA 3.0
2016-08-16T17:11:13.017Z
Is it higher like 100.4% or higher like 400%? Also, please provide more specific information about the dataset.
milancurcic
CC BY-SA 3.0
2016-08-16T17:41:18.977Z
@milancurcic no they are just a few 1-2% higher but it shows the bias of the dataset compared to other data set where RH is never over 100%
Herman Toothrot
CC BY-SA 3.0
2016-08-16T18:56:32.010Z
@user4050 please do edit that additional information into the question
410 gone
<meteorology><humidity>
Can relative humidity be over 100% near (within 30-60m) the surface?
Herman Toothrot
# Can relative humidity be over 100% near (within 30-60m) the surface?

(Asked by: username_0 on 2016-08-16)

I am processing a big meteorological data set, which is a global forcings dataset derived by other datasets and observations, and calculating relative humidity from qair,temperature, and pressure according to these formulas [How do I convert specific humidity to relative humidity?](https://earthscience.stackexchange.com/questions/2360/how-do-i-convert-specific-humidity-to-relative-humidity)

I am noticing that I have a lot of occurrences where RH is slightly higher than 100% and I am wondering if this makes sense or not considering this is air temp from 2m, I would expect that near surface RH over 100% is some errors in the data set.

\*I am not a climatologist nor a meteorologist, I use this data to study plants, so I hope for a not too technical answer, thank you.

**Tags:** meteorology, humidity

> **Comments:**
> **username_1**: Is it higher like 100.4% or higher like 400%? Also, please provide more specific information about the dataset.  
> **username_0**: @username_1 no they are just a few 1-2% higher but it shows the bias of the dataset compared to other data set where RH is never over 100%  
> **username_2**: @user4050 please do edit that additional information into the question  

---

## 2 answers

### Answer by username_3 on 2016-08-16. Score: 2

It is reasonable to assume that air (atmosphere) acting as as a solution could become supersaturated with water vapor. Supersaturation condition is where the air literally contains more water vapor than is needed to cause saturation. How common these conditions might be, I do not know.


---

### Answer by username_4 on 2016-08-18. Score: 1

The relative humidity is the ratio of the partial vapour pressure of air, to the equilibrium vapour pressure over pure water, at the same pressure - yes, it's slightly pressure dependent.But I would put an emphasis upon '*Equilibrium*'. In both physics and chemistry one can get all kinds of bizarre results under non-equilibrium conditions, and >100% RH is one of them. It is just a transient feature caused by rapid changes in temperature, pressure, or absolute vapour pressure, and as such it is not really a genuine meteorological observation.

Also, I advise caution when interpreting RH results. There is often a strong diurnal variation in RH, so if there is a met site taking only one reading a day, it could be unrepresentative of true average conditions. This is not so much a problem in advanced countries, where the measurements are (usually) reliably taken at set times. But it is often wildly misleading in developing countries where the observer may take a reading when/if he/she gets around to it, or maybe fakes the data altogether!


---

