# [ncl-talk] hovmoller diagrams for vectors and swap x/y axes

LI Qi liqi123sh at qq.com
Thu Jul 23 21:29:05 MDT 2015

```Hi Dave,
It works like a charm! Thank you very much!

Sorry for my misleading expression...what I really want is to swap the X/Y axes, i.e., to make the Time-latitude plot to a Latitude-time plot.

Then I reorder the variable's dimensions, like:

; variable's original order (time, lat, lon)
qu  = in->quz(:,:,0)
; reorder (lat, time)
qu_new = qu(lat | :, time | :)

But the figure's coordinate doesn't show latitudes and timeline (shown below). What do I do? Or is there any other way to swap the axis?

Thanks again!
Qi

------------------ Original ------------------
Date:  Fri, Jul 24, 2015 02:28 AM
To:  "David Brown"<dbrown at ucar.edu>;
Cc:  "LI Qi"<liqi123sh at qq.com>; "ncl-talk"<ncl-talk at ucar.edu>;
Subject:  Re: [ncl-talk] hovmoller diagrams for vectors

Hi Qi,

Adding to Dave's email: If you want to reverse your X/Y axes you can set trYReverse / trXReverse:
www.ncl.ucar.edu/Document/Graphics/Resources/tr.shtml#trXReverse
www.ncl.ucar.edu/Document/Graphics/Resources/tr.shtml#trYReverse

On Thu, Jul 23, 2015 at 11:58 AM, David Brown <dbrown at ucar.edu> wrote:
Hi Qi,I am guessing you need to set vcMapDirection to False. This needs to be set when you plot vectors with axes with coordinates that are not geographic.
-dave

On Thu, Jul 23, 2015 at 4:01 AM, LI Qi <liqi123sh at qq.com> wrote:

Thank you very much! The example is very helpful! I use the function "overlay" to superimpose vectors over contours.

However, the vectors seem different with the one I plot using GrADS (see below), and I don't know why. Could you help me look at my script? One more question is, how to reverse the X-Y coordinates?
Attached is the data if it is needed.

Much appreciated and best regards,
Qi

ncl plot:

my script:
;************************************************
begin
;************************************************
; variable and file handling
;************************************************
qu  = in->quz(:,:,0)
qv  = in->qvz(:,:,0)
qdiv  = in->qflxdiv(:,:,0)
time  = in->time
lat = in->lat

;************************************************
; plotting
;************************************************
wks  = gsn_open_wks("eps","eri-qhov")                ; Opens a eps file
;gsn_define_colormap(wks,"WhiteBlueGreenYellowRed")             ; choose colormap

res           = True
res at gsnDraw   = False
res at gsnFrame  = False
;
; Set up some contour resources.
;
; Turn on contour fill, and turn other things off.
;
res at cnFillOn             = True
res at cnLinesOn            = False
res at cnInfoLabelOn        = False

;
; Define contour levels and their colors.
;
;cnres at cnLevelSelectionMode = "ManualLevels"
;cnres at cnMinLevelValF       = 980.0
;cnres at cnMaxLevelValF       = 1040.0
;cnres at cnLevelSpacingF      = 5.0
;cnres at cnFillPalette        = "StepSeq25"   ; assign color map to contours

res at trYReverse           = True ; time from top to bottom, small to big
; Set special resources for the time axis
resTick                = True
resTick at ttmFormat      = "%d %c" ; form like "1 Jun", %d means day, %c means calendar
resTick at ttmAxis        = "YL" ; Y axis, Left

; Set resources necessary to customize Y axis labels
time_axis_labels( time,  res, resTick )

vecres                  = True            ; vector only resources
vecres at gsnDraw   = False
vecres at gsnFrame  = False
vecres at vcRefMagnitudeF  = 600000              ; define vector ref mag
vecres at vcRefAnnoOrthogonalPosF = -.535    ; move ref vector into plot

cnid = gsn_csm_contour(wks,qdiv,res)
vcid = gsn_csm_vector(wks,qu,qv,vecres)
overlay(cnid,vcid)
maximize_output(wks,True)
end

------------------ Original ------------------
Date:  Tue, Jul 21, 2015 04:02 AM
To:  "LI Qi"<liqi123sh at qq.com>;
Cc:  "ncl-talk"<ncl-talk at ucar.edu>;
Subject:  Re: [ncl-talk] hovmoller diagrams for vectors

Hi Qi,

I believe you will want to use the gsn_csm_vector_scalar plotting function. For an example showing how this function is used see example #6 here:
http://www.ncl.ucar.edu/Applications/overlay.shtml#ex6

(see the overlay_6_new.ncl script)

This example does not show a latitude/time plot but gsn_csm_vector_scalar should still work for your needs.

Hope that helps. If not or if you have further questions please respond to ncl-talk.

On Sat, Jul 18, 2015 at 7:29 PM, LI Qi <liqi123sh at qq.com> wrote:
Dear NCL community,

I would like to create latitude vs. time plot for moisture flux in vectors.
But the function gsn_csm_lat_time seems to be used for scalar fieids.

The data I have contains (qu,qv) over a limited area.
Below is a figure I plotted using GrADS for reference. How could I plot it using NCL?

Any suggestion would be much appreciated!

Best,
Qi

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--

Associate Scientist,  Climate and Global Dynamics Laboratory, NCAR

www.cgd.ucar.edu/staff/asphilli/   303-497-1726

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--

Associate Scientist,  Climate and Global Dynamics Laboratory, NCAR

www.cgd.ucar.edu/staff/asphilli/   303-497-1726
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