  We consider the guaranteed physics of horizontal (hadron) air-showers, HAS,
developing at high (tens km) altitudes. Their morphology and information traces
are different from vertical ones. Hundreds of km long HAS are often split by
geomagnetic fields in a long (fan-like) showering with a twin spiral tail. The
horizontal fan-like airshowers are really tangent and horizontal only at North
and South poles. At different latitude these showering plane are turned and
inclined by geomagnetic fields. In particular at magnetic equator such tangent
horizontal East-West airshowers are bent and developed into a vertical fan
air-shower, easily detectable by a vertical array detector (hanging elements by
gravity). Such "medusa" arrays maybe composed by inflated floating balloons
chains. The light gas float and it acts as an calorimeter for the particles,
while it partially sustains the detector weight. Vertically hanging chains as
well as rubber doughnut balloons (whose interior may record Cherenkov lights)
reveal bundles of crossing electron pairs. Such an array maybe loaded at best
and cheapest prototype in common balloons tracing upward and tangent hadron
air-showers from terrestrial atmosphere edge. These array structure may reveal
the split shower signature. Better revealing the composition nature. Just
beyond the Earth horizons there are exciting, but rarer, sources of upward
airshowers: the new UHE Tau Air-showers astronomy originated within Earth by
EeVs tau neutrino signals skimming the soil and forming UHE Tau, decaying later
in flight. Therefore Horizontal airshowers at equator may show the hadron
horizontal twin split nature, its composition as well as a very first expected
UHE Neutrino astronomy.
