  The electronic properties of a Kondo impurity are investigated in a magnetic
field using linear response theory. The distribution of electrical charge and
magnetic polarization are calculated in real space. The (small) magnetic field
does not change the charge distribution. However, it unmasks the Kondo cloud.
The (equal) weight of the d-electron components with their magnetic moment up
and down is shifted and the compensating s-electron clouds don't cancel any
longer (a requirement for an experimental detection of the Kondo cloud). In
addition to the net magnetic polarization of the conduction electrons an
oscillating magnetic polarization with a period of half the Fermi wave length
is observed. However, this oscillating magnetic polarization does not show the
long range behavior of Rudermann-Kittel-Kasuya-Yosida oscillations because the
oscillations don't extend beyond the Kondo radius. They represent an internal
electronic structure of the Kondo impurity in a magnetic field. PACS: 75.20.Hr,
71.23.An, 71.27.+a
