Radiative Nonideal MHD Simulations of Inner Protoplanetary Disks: Temperature Structures, Asymmetric Winds, and Episodic Surface Accretion

TL;DR

This paper advances the understanding of inner protoplanetary disks by performing global 2D MHD simulations that include all major nonideal MHD effects and a tractable radiative transfer scheme. The authors demonstrate that irradiation heating, amplified by magnetically launched winds, largely controls the disk temperature, while accretion heating via Joule dissipation is comparatively inefficient, especially near the midplane. The Hall effect introduces polarity-dependent wind asymmetries and episodic surface accretion, with the positive polarity producing strong, asymmetric winds and cyclic clump-driven accretion near the surface. These results have tangible implications for observable disk winds, shadowing, snowline locations, and molecular survival in XUV-irradiated winds, offering testable predictions for JWST and other facilities.

Abstract

We perform two-dimensional global magnetohydrodynamic (MHD) simulations including the full nonideal MHD effects (Ohmic diffusion, Hall effect, and ambipolar diffusion) and approximate radiation transport to understand the dynamics and thermal structure of the inner protoplanetary disks (PPDs). We have developed a simple radiative transfer model for PPDs that reasonably treats stellar non-thermal (XUV), stellar thermal (optical/infrared), and re-emitted radiations, reproducing the temperature structures from Monte Carlo radiative transfer. Our simulations show fast one-sided surface accretion ($\sim 10\%$ of Keplerian velocity) and asymmetric disk winds when the vertical magnetic field is aligned with the disk angular momentum. The asymmetry is due to the failure of the wind on the side with the accretion layer. On the accreting surface, clumps are repeatedly generated and accrete, driven by radiative feedback. For the anti-aligned fields, surface accretion becomes more moderate and time-variable, while the winds remain largely symmetric. For the thermal structure, accretion heating does not affect the disk temperature in any of our runs. This is because (1) the accretion energy dissipates via Joule heating at 2--3 gas scale heights, where low optical depth enables efficient radiative cooling, and (2) the winds remove $\gtrsim 10\%$ of the accretion energy. In contrast, the winds enhance radiative heating by elevating the irradiation front. These results highlight the importance of coupling between gas dynamics and radiation transport in PPDs, and provide observable magnetic activities such as fast episodic accretion, wind asymmetry, and molecular survival in XUV-irradiated winds.

Figures (21)

• Figure 1: Two-dimensional dynamical structures of the inner region at $t = 365$ yr, in FidNoH run. (a): gas density normalized by the initial midplane density with the surfaces of $\tau_{r, \rm xuv} = 1$ (purple dotted line), $\tau_{ r, \rm irr} = 1$ (blue dotted-dashed), $\tau_{\theta, \rm disk} = 1$ (red dashed), and the disk region $z = 5 H_{\rm mid}$ (white dashed). Thin lines threading to the disk show the poloidal magnetic field. (b): Mach number of the radial gas velocity, with the poloidal field line. The white solid line represents the location where the poloidal speed $|\bm{v}_{\rm pol}|$ reaches the poloidal Alfvén velocity (Alfvén surface). The arrows show the poloidal velocity direction (black: subsonic, white: supersonic). (c): toroidal magnetic field normalized by the initial magnetic field strength at the midplane, with the poloidal field line. Green contour lines correspond to the plasma beta $\beta$ = 1 (thin), and 10 (thick). (d): ambipolar Elsasser number ${\rm Am}$, with the poloidal field line. The white contours show the level of 0.1 (dashed), 1 (solid), and 10 (dotted). (e): gas temperature, with the same optical depth and height lines as in panel (a). The snow surface ($T = 170$ K) is shown in the cyan line. (f): Joule heating rate, with the poloidal field lines.
• Figure 2: Radial distributions of the time-averaged mass-accretion rate ($\left\langle\dot{M}_{\rm acc}\right\rangle\!$; black thick) and cumulative mass-loss rate ($\dot{M}_{\rm loss}$; gray thin) for the runs of FidNoH (left), FidH+ (middle), and FidH- (right). The accretion rates predicted from the wind stress $T_{\phi \theta}$ only (orange dash-dotted) and from both $T_{r \phi}$ and $T_{\phi \theta}$ (red dashed; see Equation (\ref{['eq:mdot-pred']})) are shown. The local mass loss rates (${\rm d} \dot{M}_{\rm loss} / {\rm d} \ln r$; Equation (\ref{['eq:mloss-loc']})) of the top and bottom surfaces are, respectively, shown with blue and yellow lines, with negative values indicated by dotted lines. The accretion rate and local mass-loss rate are smoothed. The shaded represents the buffer zone (see Section \ref{['ssec:simulation-setup']}).
• Figure 3: Radial distributions of the time-averaged energy change rates normalized by the energy gain in the total energy equation ($\Gamma_{\rm acc} + \Gamma_{\rm rad}$; Equations (\ref{['eq:tot-energy']})) with smoothing: the loss of the total energy ($\Lambda_{\rm wind} + \Lambda_{\rm rad}$; gray thick; Equation (\ref{['eq:tot-energy']}))), loss of mechanical energy ($\Lambda_{\rm wind, mech} + \Gamma_{\rm Joule}$; dashed light blue; Equation (\ref{['eq:mech-ene-bal']})), gain of mechanical energy ($\Gamma_{\rm acc} - Q_{\rm comp}$; red; Equation (\ref{['eq:mech-ene-bal']})), release by the disk accretion ($\Gamma_{\rm acc}$; yellow; Equation (\ref{['eq:eprod-acc']})), loss by the disk wind ($\Lambda_{\rm wind}$; dashed dark blue; Equation (\ref{['eq:Lwind']})), dissipation by Joule heating ($\Gamma_{\rm Joule}$; black; Equation (\ref{['eq:Gjoule']})), and net radiative cooling ($\Lambda_{\rm rad} - \Gamma_{\rm rad}$; gray thin; Equation (\ref{['eq:GLrad']})).
• Figure 4: Radial distributions of the but for the time-averaged midplane temperature: the simulation temperature (black), expected temperature solely due to the Joule heating rate that is calculated from the simulation ($T_{\rm Joule}$; purple dashed), the viscous disk model ($T_{\rm vis}$; Equation (\ref{['eq:Tvis']}); orange dashed), and the Static model (gray solid; see Section \ref{['sssec:static-model']}).
• Figure 5: Vertical profiles of the temperature (left), heating rate per unit volume (middle), and current density (right) at $r = 1$ au and $t = 365$ yr, for the FidNoH (top panels) and FidH+ (bottom panels). Left: simulation gas temperature (black solid; among which the contribution from re-emission is shown by blue dash-dotted), and expected temperatures due to Joule heating only (purple dashed), due to irradiation only under the Static model (gray solid), and under the simulation density and heating rate profiles (red dashed). Middle: Joule heating rate ($q_{\rm Joule}$; blue) and irradiation heating rate ($q_{\rm irr}$; orange) are shown. Gray shaded region is optically thick for disk radiation. Vertical yellow lines indicate the location of $\tau_{ r, \rm irr} = 1$. Right: magnitude of the current density (black) and the components due to global field structure (colored; see Section \ref{['sssec:current']}), where negative values are shown by dotted lines.