Complex turbulent motions of magnetized gas are ubiquitous in the interstellar medium .
The source of this turbulence , however , is still poorly understood .
Previous work suggests that compression caused by supernova shockwaves , gravity , or cloud collisions , may drive the turbulence to some extent .
In this work , we present three-dimensional ( 3D ) magnetohydrodynamic ( MHD ) simulations of contraction in turbulent , magnetized clouds from the warm neutral medium ( WNM ) of the ISM to the formation of cold dense molecular clouds , including radiative heating and cooling .
We test different contraction rates and find that observed molecular cloud properties , such as the temperature , density , Mach number , and magnetic field strength , and their respective scaling relations , are best reproduced when the contraction rate equals the turbulent turnover rate .
In contrast , if the contraction rate is significantly larger ( smaller ) than the turnover rate , the compression drives too much ( too little ) turbulence , producing unrealistic cloud properties .
The relation \sigma _ { s } ^ { 2 } = \text { ln } ( 1 + b ^ { 2 } \mathcal { M } ^ { 2 } ) between logarithmic density fluctuations ( \sigma _ { s } ) and turbulent Mach number ( \mathcal { M } ) is found to be consistent with previous theoretical models that were based on artificially-driven isothermal turbulence .
Here we find that the effective turbulence driving parameter of contraction-driven MHD turbulence subject to heating and cooling grows from solenoidal ( b \sim 1 / 3 ) to compressive ( b \sim 1 ) during the contraction .
Overall , the physical properties of the simulated clouds that contract at a rate equal to the turbulent turnover rate , indicate that large-scale contraction induced by processes such as supernova shockwaves , gravity , spiral-arm compression , or cloud collisions , may explain the origin and evolution of turbulence in the ISM .