The files in this directory contain the data presented in 

Brecht, S. H. and S. A. Ledvina, An explanation of the nightside 
     ionospheric structure of Venus, JGR, 2020

The data is stored in ASCII (text) format for easy reading.  Units
for the results are in the cgs system, densities (cm^-3), magnetic 
field (Gauss) and lengths (cm).  The magnetic field can be found 
in the B-GradPe.dat.gz.  The O+ density is designated by 2s in the 
file name.  The O2+ density is designated by 3s in the file  name.  
There are 2 types of data files, *.dat.gz and *.sdat.gz.  The *.dat 
files contain the data stored on the Cartesian grid, while the *.sdat 
contains the data stored on the spherical mesh.  See the above paper 
for details.  All the files have been compressed with gzip to reduce 
space and download times.  

The Cartesian coordinate system is set up so the x direction points
to the Sun, the y-direction points in the direction opposite to the
planets orbital motion and z completes the right handed system.  The 
Cartesian grid for the densities are (501x505x505), while for the 
magnetic fields it is (500x504x504).

The dimensions of the simulation domain are:

xlen = 3.026e9 cm = 5 Rv  
ylen = 3.026e9 cm = 5 Rv
zlen = 3.026e9 cm = 5 Rv

Venus is located at:

xx0 = 1.8156e9 cm = 3.0 Rv
yy0 = 1.5130e9 cm = 2.5 Rv
zz0 = 1.8156e9 cm = 3.0 Rv

Where Rv = 1 Venus radius = 6052 km

So to generate the grid locations with respect to the planet center
and to read the data:

The number of grid points (density):

nx = 501
ny = 505
nz = 505

Cell size

dx = xlen / (nx-1)
dy = ylen / (ny-1)
dz = zlen / (nz-1)

So to generate the planet centered locations:

do k = 1,nz
   zp = (i-1)*dz - zz0
   do j = 1,ny
      yp = (j-1)*dy - yy0
      do i = 1,nx
         xp = (i-1)*dx - xx0

         x(i,j,k) = xp
         y(i,j,k) = yp
         z(i,j,k) = zp

      enddo
   enddo
enddo

To read the Cartesian O+ density for example:

open(10,file='Den2s-GradPe.dat',status='old')

do k = 1,nz
   do j = 1,ny
      do i = 1,nx
         read(10,*) den_Op(i,j,k)
      enddo
   enddo
enddo

The procedure is the same for the B-fields but nx, ny and nz are
reduced by 1.  The read statement becomes:

open(10,file='B-GradPe.dat',status='old')

do k = 1,nz
   do j = 1,ny
      do i = 1,nx
         read(10,*)bx(i,j,k),by(i,j,k),bz(i,j,k)
      enddo
   enddo
enddo





Density and magnetic field data on the spherical (r, theta, phi) grids 
are designated as file name.sdat.  There are 72 points along the r-axis 
spanning an altitude range of 100-450 km.  Density values at 140 and 450 
km are not reliable and should not be used.  

Theta is the polar axis, running 0-pi, with 0 at the north pole of Venus,
along the planetary axis of rotation.  There are  410 theta points.

Phi is the azimuthal angle (or longitude), 0-2pi, with 0 located at the 
meridian running through zero degrees solar zenith angle.  There are 820 
phi points with 0 and 2pi being co-located.

You will have to generate the location of the grid points.

The number of grid points

nr  =  72
nth = 410
npi = 820

The lengths of the simulation box

rlen = 710 km
thlen = pi
phlen = 2*pi

Cell size
dr = rlen / (nr-1)
dth = thlen / (nth-1)
dph = phlen / (nph-1)

So to generate the locations:

do k = 1,nr
   alt = (i-1)*dr + 100.0
   do j = 1,nth
      angle_th = (j-1)*dth
      do i = 1,nph
         angle_ph = (k-1)*dph

         r(i,j,k)  = alt
         th(i,j,k) = angle_th
         ph(i,j,k) = angle_ph

      enddo
   enddo
enddo


The data has been written using the same nested loop structure used 
above:

do k = 1,nr
   do j = 1,nth
      do i = 1,nph
         write(20,*)data1(i,j,k),data2(i,j,k),data3(i,j,k)
      enddo
   enddo
enddo

Where data1,data2 and data3 correspond to H+, O+ and O2+ for the 
densities and Br, Bth and Bphi for the magnetic fields. The magnetic 
fields have units of Gauss, to convert to nT divide by 1e5, densities 
are 1/cm^3. 

Note that the indicies spin over phi, then theta and finally r.

Please send any questions to Ledvina@berkeley.edu