The files in the data collection 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
|