Anisotropic scattering tutorial (April 2021 )

Lecture slides can be found here: http://www.astro.gla.ac.uk/~eduard/lectures/scattering/Radio_wave_scattering_kontar_lecture.pdf

Prepared by E. Kontar  

This tutorial requires SSW installation (SSW webpage: https://www.lmsal.com/solarsoft/ssw_install_howto.html).

Enable LOFAR software:

https://www.issibern.ch/teams/lofar/index.php/ssw-and-lofar-idl-software/

Also available to download from:

https://sohowww.nascom.nasa.gov/solarsoft/radio/lofar/

 If you have SSW, but not LOFAR package, add the package:

IDL> setssw_windows, /lofar

* Following instruments selected:

radio/lofar

* Mission level setup files

* Instrument level setup files

Processing:   C:\ssw\radio\lofar\setup\setup.lofar_env

* Instrument level startup files

Executing:    C:\ssw\radio\lofar\setup\IDL_STARTUP

* Personal startup files

Executing:    C:\ssw\site\setup\PERSONAL_STARTUP_WINDOWS.pro

This tutorial requires SSW installation.

Compile ray_new.pro

It is recommended to have radio and nrh packages as well (see tutorial):

IDL> .r ray_new

% Compiled module: RAY_NEW.

% Compiled module: NU_SCAT.

% Compiled module: NU_SCAT_KRUPAR.

% Compiled module: NU_SCAT_KRUPAR2.

% Compiled module: NU_SCAT_CHEN.

% Compiled module: NU_SCAT_SPANGLER.

% Compiled module: OMEGA_PE.

% Compiled module: DOMEGA_DR.

% Compiled module: DENSITY_R.

% Compiled module: RAYS_HISTOGRAM_WEIGHT.

Typing ray_new in IDL command line

IDL> ray_new

will start the code with default parameters:

IF (N_Elements(eps) NE 1 ) THEN eps=0.1

IF (N_Elements(R_init) NE 1 ) THEN R_init=1.75

IF (N_Elements(anis) NE 1 ) THEN anis=0.3

IF (N_Elements(f_ratio) NE 1 ) THEN F_ratio=1.1

IF (N_Elements(asym) NE 1 ) THEN asym=1.

E.g. one can see:

IDL> ray_new

INIT: Source located at R_source=    1.75 R_sun, Angle =    0.0 degrees

f_pe=  32.038 MHz for emission frequency=  35.241 MHz

KEY PARMETERS: eps= 0.10, Anisotropy=  0.30, Asymmetry=  1.00

% Compiled module: LINECOLORS.

% Compiled module: CHECKVAR.

% Compiled module: INT_TABULATED.

Scatterint radius =       2.0374644

scattering time=     0.053909501 sec  DT save =     0.090322976

Stopping distance for calculations=       6.9660356 R_sun

% Compiled module: DERIV.

% Compiled module: INTERPOL.

% Compiled module: AVERAGE.

% Compiled module: WHERE_NOT_MISSING.

t =        1.2129646<r> =       2.0205836 N_phot=         999 <weight>=      0.62439640

% Compiled module: MINMAX.

F =       1.0000000       1.0000000       1.0000000

t =        2.4309650<r> =       2.4365318 N_phot=         999 <weight>=      0.58994623

F =       1.0000000       1.0000000       1.0000000

t =        3.6537840<r> =       2.9122192 N_phot=         999 <weight>=      0.58606300

F =       1.0000000       1.0000000       1.0000000

t =        4.8494293<r> =       3.3971518 N_phot=         999 <weight>=      0.58544811

F =       1.0000000       1.0000000       1.0000000

t =        6.0722484<r> =       3.9030572 N_phot=         999 <weight>=      0.58530315

F =       1.0000000       1.0000000       1.0000000

t =        7.2678937<r> =       4.4032125 N_phot=         999 <weight>=      0.58525987

F =       1.0000000       1.0000000       1.0000000

t =        8.4907128<r> =       4.9182439 N_phot=         999 <weight>=      0.58524279

F =       1.0000000       1.0000000       1.0000000

t =        9.7135319<r> =       5.4356874 N_phot=         999 <weight>=      0.58523502

F =       1.0000000       1.0000000       1.0000000

t =        10.909177<r> =       5.9433014 N_phot=         999 <weight>=      0.58523105

F =       1.0000000       1.0000000       1.0000000

t =        12.131996<r> =       6.4637193 N_phot=         999 <weight>=      0.58522870

F =       1.0000000       1.0000000       1.0000000

t =        13.327642<r> =       6.8621997 N_phot=         413 <weight>=      0.56725781

F =       1.0000000      0.99999999       1.0000000

Delta t=       0.47713812

X/Y angle sizes [degrees]      0.10674991     0.095727543

direction =       89.999997 degrees and FWHM angle =       7.8364111degrees

mu_HW =       0.84499998  Theta_HW =        32.328065

Tmax=      0.75346643 Delay =      0.75346643  HM before =      0.70351285   =      0.87835037

With absorption :

X-shift [R_s]=   0.00045259320+/-    0.0072972137  Y-shift [R_s]=   -0.0087097626+/-    0.0071121223

Xsize [R_s] =      0.38079280+/-     0.024303173 Ysize [R_s]=      0.37113411+/-     0.023686731

Without absorption :

X-shift [R_s]=   0.00042476030  Y-shift [R_s]=   -0.0085844973

Xsize [R_s]=      0.38190358 Ysize [R_s]=      0.37248213

% Compiled module: ERRPLOT.

FWHM Source sizes  (x & y) [degrees] =      0.10231097     0.099715884

Source Area (ellipse) [arcmin^2]=       28.415118

Predicted FWHM source sizes [arcmin] =     0.019661552

data saved to file: fpe0032037kHz_FE0035241anis0.30eps0.100asym1.00fr1.10.sav

All completed .............................................................. OK

% Program caused arithmetic error: Floating underflow

IDL>

One can change any parameter by typing the input parameters explicitly.

Simple examples to investigate:

Harmonic emission (double plasma frequency):

IDL> ray_new, eps=0.1, anis=0.1, r_init=1.75, asym=1., f_ratio=2.0

Isotropic scattering and harmonic emission:

IDL> ray_new, eps=0.1, anis=1.0, r_init=1.75, asym=1., f_ratio=2.0

Stronger/weaker scattering changing eps=0.1-1 and harmonic emission:

IDL> ray_new, eps=0.1, anis=1.0, r_init=1.75, asym=1., f_ratio=2.0

Change the position/frequency of the source:

IDL> ray_new, eps=0.1, anis=1.0, r_init=1.75, asym=1., f_ratio=2.0

More complex examples to investigate editing the code to change e.g. density model, initial conditions, plasma temperature, number of photons, etc