  The Sun's corona is millions of degrees hotter than its 5,000 K photosphere.
This heating enigma is typically addressed by invoking the deposition at
coronal heights of non-thermal energy generated by the interplay between
convection and magnetic field near the photosphere. However, it remains unclear
how and where coronal heating occurs and how the corona is filled with hot
plasma. We show that energy deposition at coronal heights cannot be the only
source of coronal heating, by revealing a significant coronal mass supply
mechanism that is driven from below, in the chromosphere. We quantify the
asymmetry of spectral lines observed with Hinode and SOHO and identify faint
but ubiquitous upflows with velocities that are similar (50-100 km/s) across a
wide range of magnetic field configurations and for temperatures from 100,000
to several million degrees. These upflows are spatio-temporally correlated with
and have similar upward velocities as recently discovered, cool (10,000 K)
chromospheric jets or (type II) spicules. We find these upflows to be pervasive
and universal. Order of magnitude estimates constrained by conservation of mass
and observed emission measures indicate that the mass supplied by these
spicules can play a significant role in supplying the corona with hot plasma.
The properties of these events are incompatible with coronal loop models that
only include nanoflares at coronal heights. Our results suggest that a
significant part of the heating and energizing of the corona occurs at
chromospheric heights, in association with chromospheric jets.

Solar and Stellar Astrophysics