Hercules A

Hercules A
Radio-Optical View of the Galaxy Hercules A - Many thanks to: NASA, ESA, S. Baum and C. O'Dea (RIT), R. Perley and W. Cotton (NRAO/AUI/NSF), and the Hubble Heritage Team (STScI/AURA)

Tuesday, September 6, 2011

ExPRES - exoplanetary and planetary radio emission simulator

I refer to:
Hess Petin Zarka Bonfond Cecconi 2010:
and its references:

This publication describes the use of the ExPRES code to model Jovian radiation arcs. The program computes the power of the radio emission  generated by the Cyclotron Maser Instability for specified electron velocities and angular parameters.
The computations are performed at several frequencies and times, to generate a theoretical dynamic spectrum that is compared to observations.
The multipole VIP4 magnetic field model (Connerney et al. 1998) is used.

Figure 3a. Sketch of the observation geometry. The delta lambda angle (lead angle) is a fundamental parameter in the fits.

As a first approximation, the times and frequencies are measured manually using Nancay Decametric Array data:

Using the initial approximation, the software finds the line of maximum spectral power and the arc width. For each arc, about 2000 runs of the code were executed with different values of electron velocity and lead angle. The quality of the model is determined  by computing the correlation of the observations with the simulations:

Fig. 6. Correlation coefficients of the 1-bitmask of the Io-C arc observed on 7 August 1999 with the 1-bitmask of the corresponding arc simulated by the ExPRES code, as a function of the emitting electrons velocity and lead angle of the radio emitting field line. The highest correlation coefficients align on a diagonal due to the geometrical balance of the lead angle and the beaming angle.

32 Io-B and 20 Io-D arcs between 1991 and 2007 were the main events analyzed in this study:

Some conclusions:

The loss cone driven Cyclotron Maser Instability models the southern hemisphere arcs with high correlation coefficients. Northern hemisphere arcs are not well modeled. The VIP4 magnetic field model does not reach a high enough value in the northern hemisphere for good fits with ExPRES.

The main ultra violet auroral spots do not have  radio arcs associated with them, as previously assumed !

In 6 spectra with multiple arcs, a regular decrease in the lead angle and electron velocity was measured.

The accuracy of the models will be improved with magnetic field models based on forthcoming Juno Observatory data.
I have not reviewed many very interesting discussions and conclusions. Please study this wonderful paper !