Characteristics of Arctic low-tropospheric humidity inversions based on radio soundings

T Nygård,T Vihma,T Valkonen

doi:10.5194/acp-14-1959-2014

Abstract

Abstract. Humidity inversions have a high potential importance in the Arctic climate system, especially for cloud formation and maintenance, in wide spatial and temporal scales. Here we investigate the climatology and characteristics of humidity inversions in the Arctic, including their spatial and temporal variability, sensitivity to the methodology applied and differences from the Antarctic humidity inversions. The study is based on data of the Integrated Global Radiosonde Archive (IGRA) from 36 Arctic stations between the years 2000 and 2009. The results indicate that humidity inversions are present on multiple levels nearly all the time in the Arctic atmosphere. Almost half (48%) of the humidity inversions were found at least partly within the same vertical layer with temperature inversions, whereas the existence of the other half may, at least partly, be linked to uneven vertical distribution of horizontal moisture transport. A high atmospheric surface pressure was found to increase the humidity inversion occurrence, whereas relationships between humidity inversion properties and cloud cover were generally relatively weak, although for some inversion properties they were systematic. For example, humidity inversions occurred slightly more often and were deeper under clear sky than in overcast conditions for almost all stations. The statistics of Arctic humidity inversion properties, especially inversion strength, depth and base height, proved to be very sensitive to the instruments and methodology applied. For example, the median strength of the strongest inversion in a profile was twice as large as the median of all Arctic inversions. The most striking difference between the Arctic and Antarctic humidity inversions was the much larger range of the seasonal cycle of inversion properties in the Arctic. Our results offer a baseline for validation of weather prediction and climate models and also encourage further studies on humidity inversions due to the vital, but so far poorly understood, role of humidity inversions in Arctic cloud processes.

Highlights

Atmospheric water vapour has major impacts on the Earth’s surface energy balance through radiative fluxes and cloud formation
Humidity inversion layers below 500 hPa are identified from the specific humidity profiles, which are calculated from the observed water vapour pressure and air pressure profiles of Integrated Global Radiosonde Archive (IGRA)
When applying the same type of data and analysis, we find that the humidity inversions are about common in the Arctic and Antarctic and have a similar seasonal cycle of the base height that is higher in the summer than in the winter, the ranges of the seasonal cycle are different

Summary

Introduction

Atmospheric water vapour has major impacts on the Earth’s surface energy balance through radiative fluxes and cloud formation. The amount of water vapour typically decreases with height, but in polar regions, layers with the amount of water vapour increasing with height have been found to be very common and simultaneously occur on multiple levels (Devasthale et al, 2011; Vihma et al, 2011; Kilpeläinen et al, 2012; Nygård et al, 2013). These humidity inversions have many important implications for cloud growth and persistence in the Arctic. In addition to implications for clouds, humidity inversions notably influence longwave radiation characteristics in clear-sky conditions (Devasthale et al, 2011)

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Discussion

Conclusion