Antarctic Low-Tropospheric Humidity Inversions: 10-Yr Climatology

Abstract

Humidity inversions are nearly permanently present in the coastal Antarctic atmosphere. This is shown based on an investigation of statistical characteristics of humidity inversions at 11 Antarctic coastal stations using radiosonde data from the Integrated Global Radiosonde Archive (IGRA) from 2000 to 2009. The humidity inversion occurrence was highest in winter and spring, and high atmospheric pressure and cloud-free conditions generally increased the occurrence. A typical humidity inversion was less than 200 m deep and 0.2 g kg 21 strong, and a typical humidity profile contained several separate inversion layers. The inversion base height had notable seasonal variations, but generally the humidity inversions were located at higher altitudes than temperature inversions. Roughly half of the humidity inversions were associated with temperature inversions, especially near the surface, and humidity and temperature inversion strengths as well as depths correlated at several stations. On the other hand, approximately 60% of the humidity inversions were accompanied by horizontal advection of water vapor increasing with height, which is also a probable factor supporting humidity inversions. The spatial variability of humidity inversions was linked to the topography and the water vapor content of the air. Compared to previous results for the Arctic, the most striking differences in humidity inversions in the Antarctic were a much higher frequency of occurrence in summer, at least under clear skies, and a reverse seasonal cycle of the inversion height. The results can be used as a baseline for validation of weather prediction and climate models and for studies addressing changes in atmospheric moisture budget in the Antarctic.

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

“…Devasthale et al (2011) found a clear nonlinear relationship between humidity and temperature inversion strength in all seasons except during summer in the Arctic. Similarly, Nygård et al (2013) found a connection between humidity and temperature inversion strength, as well as between humidity and temperature inversion depth, in the coastal Antarctic. On the other hand, the base height of humidity inversions has been reported to be generally higher compared to the base height of temperature inversions in polar regions Nygård et al, 2013).…”

“…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 also notably influence longwave radiation characteristics in clear-sky conditions (Devasthale et al, 2011). Nygård et al (2013) summarized that humidity inversions in the Antarctic coastal zone are formed and supported by condensation, horizontal advection of water vapour, turbulence and large-scale vertical motions. Condensation, which is related to the temperature control of saturation pressure, is therefore also linked to the presence of temperature inversions (Wetzel and Brümmer, 2011;Sedlar et al, 2012;Tjernström et al, 2012;Nygård et al, 2013).…”

“…Nygård et al (2013) summarized that humidity inversions in the Antarctic coastal zone are formed and supported by condensation, horizontal advection of water vapour, turbulence and large-scale vertical motions. Condensation, which is related to the temperature control of saturation pressure, is therefore also linked to the presence of temperature inversions (Wetzel and Brümmer, 2011;Sedlar et al, 2012;Tjernström et al, 2012;Nygård et al, 2013). Devasthale et al (2011) found a clear nonlinear relationship between humidity and temperature inversion strength in all seasons except during summer in the Arctic.…”

Reactive bromine in the low troposphere of Antarctica. Estimations at two research sites

“…2.2.2) and corresponds to a mean value of 1 pmol mol -1 . Note that, although the definition of the height of the boundary layer over ice and snow surfaces (e.g., Anderson and Neff, 2008) is out of the scope of this work, the BrO detection limit here provided may be regarded as an upper limit of BrO in the free troposphere since former studies place the top of the boundary layer in Antarctica between 100 m and 2 km, depending on the boundary layer parametrization and time of the year (e.g., King et al , 2006;Nygård et al, 2013). This upper limit of BrO in the free 5 troposphere of Antarctica is consistent with the few previous studies of the vertical distribution of this trace gas in the Arctic and Antarctic regions that set upper limits of BrO in the polar free troposphere of 1.5 and 2 pmol mol -1 , respectively (e.g., Frieß et al, 2011;Prados-Roman et al, 2011;Peterson et al, 2017;Hüneke et al, 2017).…”