Measurements of water vapor and cloud water/ice

Since 2005 we deploy a custom-made instrument that simultaneously measures water vapor (H2O) and cloud water/ice on board the IAGOS-CARIBIC passenger aircraft. It uses two measurement techniques:

  • a 2-channel photo-acoustic laser spectrometer (PAS) developed at the Department of Op-tics and Quantum Electronics at the University Szeged (Hungary)
  • a commercial chilled-mirror frost point hygrometer FPH (CR2, Buck Research, Boulder, USA), serving as calibration unit for the PAS laser spectrometer

A typical cross section is depicted on the figure below (right).

Cross-section of water vapour (blue), total water vapour (red) and cloud water/ice (dark green, right y-axis) during a flight from Munich (Germany) to Sao Paulo (Brazil) in 2016. The gray band indicates 100% saturation vs. ice (lower boundary) and liquid (upper boundary). Within clouds the blue line lies on the 100% saturation line for ice, that is, the aircraft flew through ice (cirrus) clouds.