  The dynamical coupling between the solar chromospheric plasma and magnetic
field is investigated by numerically solving a fully self-consistent,
two-dimensional initial-value problem for the nonlinear collisional MHD
equations including electric resistivity, thermal conduction, and, in some
cases, gas-dynamic viscosity. The processes in the contact zone between two
horizontal magnetic fields of opposite polarities are considered. The plasma is
assumed to be initially motionless and having a temperature of 50,000 K uniform
throughout the plasma volume; the characteristic magnetic field corresponds to
a plasma $\beta\gtrsim 1$. In a physical-time interval of 17~seconds typically
covered by a computational run, the plasma temperature gradually increases by a
factor of two to three. Against this background, an impulsive (in 0.1 seconds
or less) increase in the current-aligned plasma velocity occurs at the site of
the current-layer thinning (sausage-type deformation, or $m=0$ pinch
instability). Such a "velocity burst" can be interpreted physically as an event
of suprathemal-proton generation. Further development of the sausage
instability results in an increase in the kinetic temperature of the protons to
high values, even to those observed in flares. The form of our system of MHD
equations indicates that such increases are a property of the exact solution of
the system at an appropriate choice of the parameters. Magnetic reconnection
does not manifest itself in this solution: it would generate flows forbidden by
the chosen geometry. Therefore, the pinch-sausage effect can act as an
energiser of the upper chromosphere and be an alternative to the
magnetic-reconnection process as the producer of flares.
