# Moisture potential vorticityΒΆ

The example to calcluate moisture potential vorticity.

```# Calculate moisture potential vorticity
# Set working directory
trajDir = 'D:/Temp/HYSPLIT'
meteoDir = r'U:\data\ARL\2015'

# Open meteorological data file
print 'Open meteorological data file...'
meteofn = os.path.join(meteoDir, 'gdas1.mar15.w5')
print 'Meteorological file: ' + meteofn

latlim = '10:60'
lonlim = '60:140'
rh = meteof['RELH'][:,:,latlim,lonlim]
nt,nz,ny,nx = rh.shape
lat = rh.dimvalue(2)
lev = rh.dimvalue(1)
t0 = meteof['TEMP'][:,:nz-1,latlim,lonlim]
uwnd = meteof['UWND'][:,:nz-1,latlim,lonlim]
vwnd = meteof['VWND'][:,:nz-1,latlim,lonlim]
vort = hcurl(uwnd, vwnd)
prs = zeros([nt,nz,ny,nx])
prs = dim_array(prs, rh.dims)
for i in range(nz):
prs[:,i,:,:] = lev[i]

# Calculate pseudo-equivalent potential temperature
print 'Clalulate pseudo-equivalent potential temperature...'
es = 6.1078*exp(17.2693882*(t0-273.16)/(t0-35.86))
qq = rh*(0.62197*es/(prs-0.378*es))/100.
e = prs*qq/(0.62197+qq)+1e-10
tlcl = 55.0+2840.0/(3.5*log(t0)-log(e)-4.805)
theta = t0*pow((1000/prs),(0.2854*(1.0-0.28*qq)))
eqt = theta*exp(((3376./tlcl)-2.54)*qq*(1.0+0.81*qq))
thse = eqt-273.15

# Calculate moisture potential vorticity
print 'Calculate moisture potential vorticity...'
mpv = zeros([nt,nz,ny,nx], dtype='double')
mpv = dim_array(mpv, rh.dims)
mpv.setdimvalue(1, lev[1:nz-1])
for t in range(nt):
tt = meteof.gettime(t)
print tt.strftime('%Y-%m-%d %H:00')
for z in range(1, nz-1):
#print '\tLevel: %i' % z
f = zeros([ny,nx])
f1 = 2*7.292*sin(lat*3.14159/180.0)*0.00001
for i in range(nx):
f[:,i] = f1
g = 9.8
dp = 100*(lev[z-1]-lev[z+1])
deqt = eqt[t,z-1,:,:]-eqt[t,z+1,:,:]
du = uwnd[t,z-1,:,:]-uwnd[t,z+1,:,:]
dv = vwnd[t,z-1,:,:]-vwnd[t,z+1,:,:]
dx1 = 2.0*6370949.0*cos(lat*3.14159/180.0)*3.14159/180.0
dx = zeros([ny,nx])
for i in range(nx):
dx[:,i] = dx1
dy = 2.0*6370949.0*3.14159/180.0
dtx = cdiff(eqt[t,z,:,:], 1)
dty = cdiff(eqt[t,z,:,:], 0)
pv1 = -g*(vort[t,z,:,:]+f)*deqt/dp
pv2 = g*((dv/dp)*(dtx/dx)-(du/dp)*(dty/dy))
pv = pv1+pv2
mpv[t,z-1,:,:] = pv.array

#Plot
axesm()
geoshow('country', edgecolor='k')
t = 0
tt = meteof.gettime(t)
z = 5
clevs = arange(-3,3.1,0.5)
layer = contourf(mpv[t,z,:,:]*1e6, clevs)
colorbar(layer)
title('Moisture potential vorticity (%i hPa)\n' % lev[z] + \
tt.strftime('%Y-%m-%d %H:00'))

print 'Finish...'
```