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Constructing derived parameters from the initial analysed EISCAT data.

As you have seen, the six directly measured parameters from incoherent scatter (Ne, Te, Ti, Vi, vin and composition) provide the basis for the derivation of many other parameters. While the derivation of many of these is a matter for the individual user, RAL does support some software to calculate a few of these "value added" products.

Velocity Combination

Combination of measured line-of-sight flows into vector velocities can be carried out using the velcom program. On the clustered machines, type

velcom -h

This will show you the syntax. By default the combination is done using a "least squares" method, so that in principle more than three velocity estimates can be combined into a single vector. An example might be the combination of velocities derived from alternating code and long pulse algorithms at each site (six estimates in total) into a single velocity.

In addition to tristatic velocities, the program can also be used to calculate velocities from multiple pointing measurements made at a single site, by the so-called "beam swinging" technique. Note that this involves gross assumptions about the spatial and temporal uniformity of the velocity field!

On the older machines, tristatic velocity combination can also be carried out using the command

ncar velcom

The syntax is

ncar velcom {var file} {output file} {input file1} {input file2} {input file3}

The inclusion of the var file above is optional. A standard var file is picked up by default.

Note that for both velcom and ncar velcom, the input and output files are in "RAL NCAR" (rslt) format.

Ionospheric Conductivities and Conductances

Introduction

Electrodynamic parameters such as conductivities, conductances, current densities and Joule heating rates can be calculated from EISCAT electron density profiles and velocities, on the basis of assumed collision models - and implicit assumptions about the parameters of the neutral atmosphere. A number of programs have been developed at RAL to calculate these quantities. Those that compute the conductivities and conductances are described here.

There are two such programs:-

The two programs are discussed in Sections 13.2.2 and 13.2.3, respectively. The provision of suitable plotting programs is currently being explored.

The programs can be found on the directory /home/user1/ken/customers/eldynam_new. They have been set up to run on the cluster computers (not the older ones), and should be copied to the user's working directory before use. One should also copy from this directory the appropriate steering file and the file ncar.var. (An explanation of the meaning and purpose of these files can be found in Section 13.2.2.) The directory also contains a number of files with the suffix "mdl". These hold the models of coefficients used by the magnetic field routines contained with condncar, and should also be copied into the user's working directory.

condncar

This program computes the Hall, Pedersen, and Longitudinal conductivities from EISCAT electron density and electron temperature profiles. To do this it employs the Alcaydé neutral atmosphere model and the IGRF 2000 model of the terrestrial magnetic field. The first of these is built into the program. The data files for the second must be provided and are in the above directory.

The plasma parameters required by condncar are obtained from a file of analysed EISCAT data in NCAR format (i.e. a rslt file). If the analysis was carried using GUISDAP, the output must first be converted into NCAR format using g2n. The output from condncar is written onto another NCAR format file.

To run the program, one must first issue the command:

export LD_LIBRARY_PATH=/soft/eiscat/lib

This provides a link to a library of NCAR routines. The command for condncar proper then follows. This is:

condncar ncar.var {data file} {steering file} {output file}

where:

The program usually runs very quickly and does not as a rule present any problems. If a difficulty is found in locating the data file and the file was kept on a stager directory and has not been used for some time, then it may have been deleted. In this case, the analysis will need to be repeated. The message:

"Fatal Error: Cannot map library libncar.so"

means that the above export command has not been given.

Conductivities can be calculated for any EISCAT experiment, although those for which the transmitter beam is aligned with the magnetic field are usually most appropriate. One should note that there is negligible conductivity above 250 km, while there may be significant Hall conductivity below 100 km. An experiment should therefore be chosen which makes measurements between the heights of 90 km and 270 km. If measurements have been made beyond these limits, it may well be advisable to restrict the analysis to the region between these two heights.

htintcnd

The function of this program is to integrate the Hall and Pedersen conductivities obtained from condncar over a range of heights. (The Longitudinal conductivity tends to infinity with increasing height so that integrating it over height is not particularly meaningful.) The result is the Hall and Pedersen conductances. The program also computes the ratio of Hall to the Pedersen conductance, which can provide a measure of the energy deposited in the ionosphere during active periods.

To run the program, type:

htintcnd {conductivity file} {conductance file}

where:- {conductivity file} is an NCAR format output file from condncar. {conductance file} is the output from htintcnd. It is also an NCAR format, but does not contain any parameters from the original analysis or even the conductivities produced by condncar. The parameters in the file are all ones which do not dependent on height.

This program also runs very quickly, and does not usually present any problems. The comments in Section 13.2.2 about the choice of an appropriate height interval apply here also. In particular, the omission of measurements below 100 km can result in the calculated Hall conductance being too small.

Steering Files

The parameters in the Steering File are as follows: Line 1: RFILE . Line 2: EFILE. Line 3: SNC, ENC. Line 4: CMIRM, CMI, CINCF. Line 5: FITAC, SLMPC, MINHC, MAXHC, HMIN, HMAX. Line 6: TEXO, TZBAZ, TM, TS. Line 7: ZBAZ, ZREF, ZM, ZS. Line 8: MMD, MLRI, MMRI.

Line 1 & 2

RFILE and EFILE are the names of the output and error files employed by an earlier version of the program. They are not used by the current version.

Line 3

Line 4

These relate to the composition and ion-neutral collision frequency models employed by the program. CMIRM is the Ion Mass Constants Code for RAL Composition Model. CMIRM = 0 to use:-

CMIRM = 1 to use:-

(CMIRM = 0 is normally used.)

CMI is the Ion Mass Calculation Code that should be set to 1. (With this, the program will use the RAL Composition Model.)

CINCF is the Ion-Neutral Collision Frequency Calculation Code where:-

(CINCF = 4 is recommended.)

Line 5

FITAC is a Fit Acceptance Code that is not used in the current program, and should be set to zero.

SLMPC selects the type of data, but is not used in the current program.

MINHC is a Minimum Height Code for which:-

MAXHC is a Maximum Height Code for which:-

HMIN is the Minimum Height for the above test in km.

HMAX is the Maximum Height for the above test in km.

(If MINHC and MAXHC are set to zero, the program computes conductivities for the entire range of heights over which the data was originally analysed. This is the option normally chosen.)

Lines 6 & 7

The parameters of Lines 6 and 7 are those required by the Alcaydé neutral atmosphere model.

Line 8

These are the molecular masses required by the parameter CMIRM in Line 4.