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We investigate, through 2D MHD numerical simulations, the interaction of auniform magnetic field oblique to a moving interstellar cloud. In particular weexplore the transformation of cloud kinetic energy into magnetic energy as aresult of field line stretching. Some previous simulations have emphasized thepossible dynamical importance of a ``magnetic shield'' formed around cloudswhen the magnetic field is perpendicular to the cloud motion (Jones et al.1996, Miniati et al. 1998). It was not clear, however, how dependent thosefindings were to the assumed field configuration and cloud properties. Toexpand our understanding of this effect, we examine several new cases by varingthe magnetic field orientation angle with respect to the cloud motion (\theta),the cloud-background density contrast, and the cloud Mach number.  We show that in 2D and with \theta large enough, the magnetic field tensioncan become dominant in the dynamics of the motion of high density contrast, lowMach number clouds. In such cases a significant fraction of cloud kineticenergy can be transformed into magnetic energy with the magnetic pressure atthe cloud nose exceeding the ram pressure of the impinging flow. We derive acharacteristic timescale for this process of energy ``conversion''. We findalso that unless the cloud motion is highly aligned to the magnetic field,reconnection through tearing mode instabilities in the cloud wake limit theformation of a strong flux rope feature following the cloud. Finally we attemptto interpret some observational properties of the magnetic field in view of ourresults.Comment: 24 pages in aaspp4 Latex and 7 figures. Accepted for publication in  The Astrophysical Journa

On the Exchange of Kinetic and Magnetic Energy between Clouds and the Interstellar Medium