Context : Nearby edge-on galaxies showing a synchrotron halo are nearly ideal objects for studying the transport of cosmic rays ( CRs ) in galaxies .
Among them , the nearby starburst galaxy NGC 253 hosts a galactic wind indicated by various ISM phases in its halo .

Aims : The diffusive and convective CR transport from the disk into the halo is investigated using the local CR bulk speed .
The connection between the CR transport and the galactic wind is outlined .

Methods : We observed NGC 253 with the VLA at \lambda 6.2 { cm } in a mosaic with 15 pointings .
The missing zero-spacing flux density of the VLA mosaic was filled in using observations with the 100-m Effelsberg telescope .
We also obtained a new \lambda 3.6 { cm } map from Effelsberg observations and reproduced VLA maps at \lambda 20 { cm } and \lambda 90 { cm } .
The high dynamic range needed due to the strong nuclear point-like source was addressed with a special data calibration scheme for both the single-dish and the interferometric observations .

Results : We find a thin and a thick radio disk with exponential scaleheights of 0.3 { kpc } and 1.7 { kpc } at \lambda 6.2 { cm } .
The equipartition total magnetic field strength between 7 { \mu G } and 18 { \mu G } in the disk is remarkably high .
We use the spectral aging of the cosmic ray electrons ( CREs ) seen in the vertical profiles of the spectral index to determine a lower limit for the global CR bulk speed as 170 \pm 70 { km s ^ { -1 } } .
The linear correlation between the scaleheights and the CRE lifetimes , as evident from the dumbbell shaped halo , requires a vertical CR transport with a bulk speed of 300 \pm 30 { km s ^ { -1 } } in the northeastern halo , similar to the escape velocity of 280 km s ^ { -1 } .
This shows the presence of a “ disk wind ” in NGC 253 .
In the southwestern halo , the transport is mainly diffusive with a diffusion coefficient of 2.0 \pm 0.2 \times 10 ^ { 29 } cm ^ { 2 } s ^ { -1 } .

Conclusions : Measuring the radio synchrotron scaleheight and estimating the CRE lifetime allow us to determine the bulk speed of the CR transport into the halo .
The transport is convective and more efficient in the northeastern halo , while it is diffusive in the southwestern halo .
The luminous material is transported by the disk wind , which can explain the different amounts of extra-planar H I , H \alpha , and soft X-ray emission in the two halo parts .
Future low-frequency radio observations will provide the data to analyze the vertical velocity profile of galactic winds .