Humidity measurements in cold and humid environments

Lasse Makkonen (Corresponding Author), Timo Laakso

    Research output: Contribution to journalArticleScientificpeer-review

    20 Citations (Scopus)

    Abstract

    Recent studies have shed new light on humidity conditions in the polar atmospheric boundary layer, and cast doubt on the reliability of humidity measurements above the frost point humidity. These issues are addressed herein by considering the processes that affect humidity and its measurement in cold climate conditions and by analyzing observations from two sites, at which the relative humidity is frequently above 100% at sub-freezing temperatures, as shown by repeatedly observed in-cloud icing events. Humidity measurements were made at these two sites by the commonly used Vaisala HMP35 probe and HMP233 capacitance probes respectively and simultaneously by the same manufacturer’s HMP243 probe that determines the frost point by a heated capacitance sensor. The results confirm that the relative humidity is frequently well above the frost point, both due to radiative cooling and to the advection of moist air, and that the conventional humidity measurements are unable to detect these events. Furthermore, after such events, the iced sensors show too high a humidity. The false values occur due to ice growth on the probe and cannot be corrected by any algorithm. Our results indicate that these problems, inherent to conventional humidity measurements in cold and humid environments, are avoided by the use of HMP243, which has a heated humidity probe.
    Original languageEnglish
    Pages (from-to)131 - 147
    Number of pages17
    JournalBoundary-Layer Meteorology
    Volume116
    Issue number1
    DOIs
    Publication statusPublished - 2005
    MoE publication typeA1 Journal article-refereed

    Keywords

    • arctic boundary layer
    • frost point
    • humidity measurements
    • hygrometers
    • icing
    • relative humidity

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