Indirect measurements of High Energy Cosmic Rays

In this review I will shortly discuss some of the latest results obtained by indirect measurements of High Energy Cosmic Rays. The field covers a wide energy range, from 1013eV up to 1020eV: the measurement techniques, the dimension of the arrays and the scientific goals of experiments are completely different. The main experimental achievements of the last years can be shortly summarized as follows. In the energy range below the knee of the primary spectrum (E<4×1015eV) an anisotropy in the arrival direction of primary particles has been discovered. Around knee energies (i.e. from 3–4×1015eVto∼1017eV) relevant new results have been obtained with the detection of a change of slope in the spectrum of heavy primaries. And finally at higher energies (above 1018eV) a flux suppression around ∼5×1019eV and also an indication of a large scale anisotropy in the cosmic ray arrival directions, for energies greater than ∼5×1019eV, have been measured.