[gradsusr] Get direction of max wind in hourly time serie of a point

[Eric Altshuler]

Hello Claudio, 


To calculate the prevailing wind direction for a day, you should average the hourly u and v components, then find the direction of this average wind vector. It's not a good idea to average the hourly wind directions because very weak winds would get the same weighting as stronger winds. On the other hand, for daily average wind speed, you should average the hourly wind speeds. 


Best regards, 



Eric L. Altshuler 
Research Scientist 
Center for Ocean-Land-Atmosphere Studies 
4041 Powder Mill Road, Suite 302 
Calverton, MD 20705-3106 
USA 

E-mail: ela at cola.iges.org 
Phone: (301) 902-1257 
Fax: (301) 595-9793 

----- Original Message -----
From: "claudiomet" <claudiomet at gmail.com> 
To: "GrADS Users Forum" <gradsusr at gradsusr.org> 
Sent: Thursday, May 30, 2013 9:47:50 PM 
Subject: Re: [gradsusr] Get direction of max wind in hourly time serie of a point 





Thanks Martin ! 

I will try the method ! 
Concening with the direction no problem, the dataset includes speed in degrees 

(It's a WRF output post-processed with ARWpost specifying the wind as u,v vectors and speed and direction) 
Thanks again ! 




2013/5/30 Martin V. Mathew < vmartinmathew at gmail.com > 




Hi 
I think you can try following two steps to obtain the direction of maximum wind. 


First you have to find the hour of the day in which have maximum wind speed (use mag and maxloc commands). http://www.iges.org/grads/gadoc/gadocindex.html 



After identifying the particular hour use trigonometric function atan2() to obtain the angle. 
http://www.iges.org/grads/gadoc/functionsatt.html 


Regards 
Martin 





On 29 May 2013 21:42, claudiomet < claudiomet at gmail.com > wrote: 

<blockquote>


Greetings users. 

I'm writing a script to extract data of a single point in ascii file 
(my data set is hourly and I'm extracting daily vaues of max temp, min 
temp, max wind, max rel hum, etc... solved). 

But my problem is that I need to obtain the direction of the wind at 
the hour of the max wind intensity and the prevailing wind of the day 
¿How can I do this? 

Thanks in advance ! 

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-- 
Martin V. Mathew 
Research scholar 
Centre for Oceans, Rivers, Atmosphere and Land Sciences (CORAL) 
IIT Kharagpur 
India. 

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</blockquote>



-- 

Claudio Cortes N. 
Project Engineer R&D 
Environmental Area 
MICOMO S.A. 
Tel: +56 (2) 22400516 
Cel: +56 (9) 65871064 
ccortes at micomo.cl 
www.micomo.cl 
Antonio Rabat Sur 6165, Vitacura 

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