A note on surface humidity measurements in the cold Canadian environment

In the cold Canadian environment, humidity measurements can be very difficult to conduct. In this brief communication, humidity observations taken by two different sensors at six remote Canadian Arctic locations are compared. The observations collected by Vaisala HMP35CF sensors display a strong tendency toward the ice saturation point whereas dew cell instruments exhibit significantly lower values of relative humidity with respect to ice (RHi). Humidity data collected by HMP35CF hygrometers are therefore unreliable since they are subject to persistent icing that lead them to record values of RHi near 100%, irrespective of the air temperature. The high humidity bias emerges at meteorological stations mounted with the HMP35CF probes since these instruments are usually neither sheltered nor heated, and are not attended to at regular intervals. Thus, great care must be taken in utilizing humidity data recorded by HMP35CF sensors across the network of climate autostations in Canada.