Electro-mechanical coupling between the photosphere and transition region

We study the response of the chromosphere and transition region to dynamic changes in the photospheric network magnetic fields. We present results fro m simultaneous measurements taken by TRACE in chromospheric and transition region (C iv) images, high-resolution magnetograms taken by MDI, and spectr a of chromospheric (C ii) and transition region lines (O vi) obtained with the SUMER instrument on SOHO. Enhanced emission in the C iv line is general ly co-spatial with the magnetic pattern in the photosphere. We propose a me chanism of electro-mechanical coupling between the photosphere and upper la yers of atmosphere based on hydrodynamic cumulation of energy produced by r econnecting flux tubes in the photosphere/chromosphere region (Tarbell et a l., 1999). We believe that a basic process causing energetic events is the cascade of shock waves produced by colliding and reconnecting flux tubes. T he continuous supply of flux tubes in the 'magnetic carpet' ensures the ubi quitous nature of this process and its imprint on the upper atmosphere. The appearance of bright transients often, but not always, correlates with can celing mixed polarity magnetic elements in the photosphere. In other cases, transients occur in regions of unipolar flux tubes, suggesting reconnectio n of oblique components. Transients are also seen in regions with no fields detected with the MDI sensitivity; these may be reconnections of tiny feat ures with diameters less than 100 km. Blinkers and other bright transients are often accompanied by two directional plasma jets. These may be generate d by cylindrical self-focusing of shock fronts or by collision of shocks pr oduced by neighboring reconnection processes. The observations suggest that stronger emissions correspond to lower velocity jets, and vice versa; this property is a natural consequence of the proposed mechanism. Plasma flows are always seen whenever the slit crosses strong magnetic flux tubes or ver tices of converging flows in the supergranular network. The overall energy distribution between heating and plasma flows is an intrinsic feature of ou r mechanism.