Solar Cycle 24 Group H

From RHESSI Wiki

Jump to: navigation, search



Fletcher: chromosphere is important for flares; energy must come through the chromosphere, need focus on diagnostics & modelling.

20081209: Scott McIntosh

Phase travel time around spots show travel time varies with B, phi.

Bigger ring at 2 mHz around spot, smaller ring at 4 mHz closer to umbra.

Halpha spicules/dynamic fibrils show leaking p-modes around plage in inclined field.

x-t plots show parabolas: shocks are propelling mass up, verification through simulations.

Other option for wave propagation: radiative losses.

Original idea by Roberts to explain Giovanelli.

Internal gravity waves from Bob Stein's simulations.

IGWs are ubiquitous, see through k-f filtering, very energetic.

Alfvén waves are ubiquitous in the corona, but only 5-minute periods (COMP).


What do we need? Spatially resolved spectrometry.


Key objectives: energy and mass transport in the chromosphere.

20081209: Rebecca Centeno

Study wave propagation using He 10830.

Slit on plage, includes Si line in the photosphere.

5-minute p-modes in the photosphere.

He shows 3-minute oscillations in sunspot-like structures in the chromosphere, amplitude ~ B.

He shows 5-minute oscillations in plage.

In sunspots: Delta phi < 2 mHz no signal, < 4 mHz evanescent, < ... propagation

Use simple model: isothermal T, constant B // g, radiative losses.

Play with model parameters until it matches the observations.

In plage: taur = 10 s (short!), T = 9500 K (high!), Delta z = 1500 km

Discussion on field inclination: these results show theta = 0.

No resolution on correlation with SP that shows theta = 0 happens rarely.

20081209: Alfred de Wijn

Sorry, too boring, I fell asleep.

20081209: Lyndsay Fletcher

Question: can we diagnose flare inputs?

Optical radiation produced in flares is compact and intense.

We would really like to have an estimate of energy input.

How well can we estimate the total energy input?

Energy transport:

What happens when a strong Alfven pulse hits the chromosphere?

20081210: Phil Judge

Basic question: why does the sun produce the chromosphere etc. as it is?

All stars with surface convection have chromospheres.

Observationally driven research.

Some stars emit more in the corona than in the chromosphere, so cannot ignore the corona.

Spicules span 9 scale heights, spicules arise from the chromosphere, aren't part of it.

Heating: steady current systems are not dominant.

Chromosphere is partially ionized plasma, leads to frictional dissipation through ion-neutral coupling.

Dissipation of jperp tries to make field force free in the chromopshere.

Chromosphere is bright in network, so high p where high B (VAL/FAL).

But: magnetostatic models require low p where high B.

Twist naturally increases with height because of conservation of flux and current.

Claim has been made that the chromosphere and corona are not connected.

Cool loop explanation, but where does 106 erg/cm2/s conductive flux go?

TR radiates 106 erg/cm2/s, coincidence?

VAULT results show Ly alpha is from the base of hot coronal loops.

Neutral diffusion as a way to explain Ly alpha emission?

Critical question: what are the chromospheric conditions at the base of the corona?

Need B measurement in the chromosphere.

Way forward: integral field spectroscopy to get B in the chromosphere.

Discussion: interpretation of measurements (e.g., 10830) is difficult.

20081210: Thomas Straus

4 kW/m2 needed to heat the chromosphere.

<10% acoustic waves (Fossum & Carlsson 2005)

90% "magnetic"

Energy transport in 1D: acoustic waves above cut-off frequency.

Energy transport in 3D: acoustic waves above cut-off frequency + IGWs.

Study IGWs in observations and simulations.

Energy flux: rho <v2> vgr for observations, <p vz> for simulations.

In simulations: lots of energy in IGWs, some in f-mode, little in acoustic.

Acoustic flux is insufficient.

Above 300 km all flux is in IGWs.

Target flux is achieved.


What is the science case for the future? Open games:

20081210: Discussion

20081211: Mats Carlsson

Boundaries for simulations:

Energy balance:

Other complications: chromosphere is mostly neutral, may require multi-fluid approach.

Impossible to solve the full problem from a practical point of view, so make approximations and solve a suitable sub-problem.

RT post-processing OK in the photosphere, but not so good in the chromosphere because the simulation is not realistic there.

Discussion: simulated "observations" may be confusing because of differences in representation with real observations.

Discussion: current status of heating problems: corona is ok, not enough in the chromosphere.

20081211: Tony Arber

What's the minimum physics we need to make a realistic chromosphere?

Include neutrals results in "almost MHD".

Disregard ion-neutral slip in the chromosphere.

E + v x B = eta j turns into E + v x B = eta jpar + etacowling jperp

In the chromosphere etacowling dominates.

Results from including neutrals:

Cowling conductivity cannot be written as a diffusion equation.

Chromosphere cannot support equilibrium unless force-free.

Neutrals intensify current concentrations, so more reconnection.

20081211: Hiroaki Isobe

Poynting flux of THMF ~ 2*106 erg/cm2/s is approx. required to heat the chromosphere.

Conclusion from simulations: need multi-fluid with neutrals.

Chromospheric reconnection? Weakly ionized and fully collisional, is fast reconnection possible?

Ion-neutral collisions increase the reconnection rate, see Tony's talk.

20081211: Bill Abbett

Linking convection to the corona requires a chromosphere.

At large scales it is not possible to treat the physics properly in the chromosphere.

So what is the minimum requirement to get the connection from the photosphere to the corona right?

In this work, <j . B> is lowest in the photosphere where we measure B, i.e., possibly the worst place to measure!

20081211: Bart De Pontieu

Type II spicules explanation.

Look for upflow events (Hara) in EIS data: no correlation with intensity, occur at footpoints of loops.

Correlation between type II spicules and upflows, not great but not expected because of viewing angle issues.

So do type II spicules fill the corona with mass?

Coronal evaporation linked to type II spicules.

Personal tools