[ncl-talk] Wind barb orientation in python plots

[Zilore Mumba]

Just to illustrate my point I attach the output

On Thu, Aug 26, 2021 at 10:04 AM Zilore Mumba <zmumba at gmail.com> wrote:

> I am wondering if python does not recognise that wind barbs are directed
> to the right in the southern hemisphere and to the left in the northern
> hemisphere. This is the same problem in ncl which seems to be carried over
> to python.
> If it is possible to change this I would appreciate assistance. I
> reproduce below a script to plot 850 winds, if it is possible to indicate
> where to make any change.
>
> from netCDF4 import Dataset
> import cartopy.io.shapereader as shpreader
> import numpy as np
> import matplotlib.pyplot as plt
> from mpl_toolkits.axes_grid1 import make_axes_locatable
> from matplotlib.cm import get_cmap
> import cartopy.crs as crs
> from cartopy.feature import NaturalEarthFeature
>
> from wrf import (getvar, interplevel, to_np, latlon_coords, get_cartopy,
>  cartopy_xlim, cartopy_ylim)
>
> #Open the NetCDF file
> #--------------------
> ncfile = Dataset("wrfout_d01_2021-08-19_06:00:00")
>
> #Extract the pressure, geopotential height, and wind variables
> #-------------------------------------------------------------
> p = getvar(ncfile, "pressure")
> z = getvar(ncfile, "z", units="dm")
> ua = getvar(ncfile, "ua", units="kt")
> va = getvar(ncfile, "va", units="kt")
> wspd = getvar(ncfile, "wspd_wdir", units="kts")[0,:]
>
> #Interpolate geopotential height, u, and v winds to 850 hPa
> #-----------------------------------------------------------
> ht_850 = interplevel(z, p, 850)
> u_850 = interplevel(ua, p, 850)
> v_850 = interplevel(va, p, 850)
> wspd_850 = interplevel(wspd, p, 850)
>
> #Get the lat/lon coordinates
> #---------------------------
> lats, lons = latlon_coords(ht_850)
>
> #Get the map projection information
> #----------------------------------
> cart_proj = get_cartopy(ht_850)
>
> #Create the figure
> #-----------------
> fig = plt.figure(figsize=(12,9))
> ax = plt.axes(projection=cart_proj)
>
> #Download and add the states and coastlines
> #-----------------------------------------
> #states = NaturalEarthFeature(category="cultural", scale="50m",
> # facecolor="none",
> # name="admin_1_states_provinces_shp")
> #ax.add_feature(states, linewidth=0.5, edgecolor="black")
> #ax.coastlines('50m', linewidth=0.8)
>
> fname = './ZMB_ADM1.shp'
> adm1_shapes = list(shpreader.Reader(fname).geometries())
>
> #Add the 850 hPa geopotential height contours
> #--------------------------------------------
> levels = np.arange(150., 155., 1.)
> contours = plt.contour(to_np(lons), to_np(lats), to_np(ht_850),
>    levels=levels, colors="blue",
>    transform=crs.PlateCarree())
> plt.clabel(contours, inline=1, fontsize=10, fmt="%i")
>
> #Add the wind speed contours
> #---------------------------
> levels = [0, 5, 10, 15, 20, 25, 30]
> wspd_contours = plt.contourf(to_np(lons), to_np(lats), to_np(wspd_850),
>  levels=levels,
>  cmap=get_cmap("rainbow"),
>  transform=crs.PlateCarree())
> plt.colorbar(wspd_contours, ax=ax, orientation="vertical", pad=.05)
>
> #divider = make_axes_locatable(ax)
> #ax_cb = divider.new_horizontal(size="5%", pad=0.1, axes_class=plt.Axes)
>
> #plt.add_axes(ax_cb)
> #plt.colorbar(wspd_contours, cax=ax_cb, pad=.05)
>
> #Add the 850 hPa wind barbs, only plotting every 5th data point.
> #-----------------------------------------------------------------
> plt.barbs(to_np(lons[::10,::10]), to_np(lats[::10,::10]),
>   to_np(u_850[::10, ::10]), to_np(v_850[::10, ::10]),
>   transform=crs.PlateCarree(), length=6)
>
>
> ax.add_geometries(adm1_shapes, crs.PlateCarree(),
>                   edgecolor='black', facecolor='gray', alpha=0.5)
>
> #Set the map bounds
> #------------------
> ax.set_xlim(cartopy_xlim(ht_850))
> ax.set_ylim(cartopy_ylim(ht_850))
>
> ax.gridlines()
>
> plt.title("850 MB Height (dm), Wind Speed (kt), Barbs (kt)")
>
> plt.show()
>
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