On the minimum temperature of the quiet solar chromosphere

¹ Sterrekundig Instituut, Utrecht University, Postbus 80 000, 3508 TA Utrecht, The Netherlands
e-mail: j.leenaarts@uu.nl
² Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029, Blindern, 0315 Oslo, Norway
³ Center of Mathematics for Applications, University of Oslo, PO Box 1053, Blindern, 0316 Oslo, Norway

Received: 22 December 2010
Accepted: 20 April 2011

Abstract

Aims. We aim to provide an estimate of the minimum temperature of the quiet solar chromosphere.

Methods. We perform a 2D radiation-MHD simulation spanning the upper convection zone to the lower corona. The simulation includes non-LTE radiative transfer and an equation-of-state that includes non-equilibrium ionization of hydrogen and non-equilibrium H₂ molecule formation. We analyze the reliability of the various assumptions made in our model in order to assess the realism of the simulation.

Results. Our simulation contains pockets of cool gas with down to 1660 K from 1 Mm up to 3.2 Mm height. It overestimates the radiative heating, and contains non-physical heating below 1660 K. Therefore we conclude that cool pockets in the quiet solar chromosphere might have even lower temperatures than in the simulation, provided that there exist areas in the chromosphere without significant magnetic heating. We suggest off-limb molecular spectroscopy to look for such cool pockets and 3D simulations including a local dynamo and a magnetic carpet to investigate Joule heating in the quiet chromosphere.