Relative humidity equation

[Din19]

@Ming Chen , I am sorry for disturbing you, but I saw your post about calculation of RH: relative humidity
I have a question , in your equation what is the difference between t and T? Does t represent T2 at 2 meters, and doesT represent 3D variable of temeprature?

 

[Ming Chen]

Indira,
I am sorry for the typo. Actually T and t are the same, which is temperature (3D variable).

 

[Din19]

Indira,
I am sorry for the typo. Actually T and t are the same, which is temperature (3D variable).

@Ming Chen Thank you very much for your reply.

 

[Din19]

Indira,
I am sorry for the typo. Actually T and t are the same, which is temperature (3D variable).

I am sorry, I have a question about QVAPOR, in this equation should all variables be 3D?

what about relative humidity at 2 meters ?Is it applicable to get relative humidity at 2 meters?

 

[Ming Chen]

This is a general equation for deriving RH from water mixing ratio and other variables. The input variable could be a single variable, could be an array of any dimension. The same formula can be used to derive RH at 2-m, too.

 

[Din19]

This is a general equation for deriving RH from water mixing ratio and other variables. The input variable could be a single variable, could be an array of any dimension. The same formula can be used to derive RH at 2-m, too.

@Ming Chen , Thank you very much for your reply.

 

[Din19]

@Ming Chen , I am sorry for disturbing you.

I extracted relative humidity at 2m using GrADS and applying the following equation: 1.E2 * (p*q2/(q2*(1.-0.622) + 0.622))/(611.2*exp(17.67*(t2-273.15)/(t2-29.65)))
Unfortunately, for one day (August 23,2018 from 06:00 till August 24,2018) I got negative relative humidity values. I checked q2 values, and they were positive.

What could be the possible reason behind the negative values of relative humidity?

I would appreciate it if you could help me.

Thank you

 

[Ming Chen]

What are the values of other variables at the site where you get negative RH?

 

[Din19]

Thank you for your reply @Ming Chen. The temeprature values t2 for this date are positive, and in the normal range. There are no problems.

However, the problem is p values. For some coordinates p value shows negative values, and most probably this is what affected the RH. I want to metion that these values are observed only for August 23,2018 from 06:00 till August 24,2018. I used ERA-Interim Reanalysis data. and ECMWF Vtable.

What could cause negative p values for some coordinates in the domain?
Thank you .

 

[Din19]

Thank you for your reply @Ming Chen. The temeprature values t2 for this date are positive, and in the normal range. There are no problems.

However, the problem is p values. For some coordinates p value shows negative values, and most probably this is what affected the RH. I want to metion that these values are observed only for August 23,2018 from 06:00 till August 24,2018. I used ERA-Interim Reanalysis data. and ECMWF Vtable.

What could cause negative p values for some coordinates in the domain?
Thank you .

Could it be related to the fact that P is 3 D variable, and t2 and q2 are 2d variables?

 

[Din19]

Thank you for your reply @Ming Chen. The temeprature values t2 for this date are positive, and in the normal range. There are no problems.

However, the problem is p values. For some coordinates p value shows negative values, and most probably this is what affected the RH. I want to metion that these values are observed only for August 23,2018 from 06:00 till August 24,2018. I used ERA-Interim Reanalysis data. and ECMWF Vtable.

What could cause negative p values for some coordinates in the domain?
Thank you .

I am sorry. If I want to get relative humidity at 2 m, should I use PSFC together with t2 and q2 in the formula(instead of p)?

 

[VladimirSobral]

This is a general equation for deriving RH from water mixing ratio and other variables. The input variable could be a single variable, could be an array of any dimension. The same formula can be used to derive RH at 2-m, too.

Hi @Ming Chen

Please could you explain again this equation below. I'm a new WRF user and would like to calculate RH (2m) in GIS software through wrfout files. I'm using NCEP GDAS/FNL 0.25 Degree Global Tropospheric Analyses and Forecast Grids as meteorological data.

Equation: 1.E2 * (p*q2/(q2*(1.-0.622) + 0.622))/(611.2*exp(17.67*(t2-273.15)/(t2-29.65)))

I understood the variables (p, q2 and t2) but what does "1.E2" mean?

Thanks.

 

[Ming Chen]

This is a typical fortran expression, 1.E2 = 100