FIR observations of stratospheric irregularities and fluctuations.

During a balloon flight at 45 km altitude, the authors found a quadrupole-like anisotropy in the stratospheric emission in the FIR, aligned in the North-South direction with a typical amplitude of 3×10^-2K. A sudden increase in the amplitude of the anisotropy was found with a time scale of 1 hr and the amplitude was found to be wavelength dependent (0.25K at 100 μm and 0.15K at 600 μm wavelength). This is consistent with an anisotropy in the water-vapour distribution of the order of 5%.