Using GPSRO to Study Arctic and Subarctic Winter Temperature Inversion Layers

The radiation balance at the earth surface is significantly affected by the continuous presence of the atmospheric boundary layer (ABL). The ABL plays the role of an atmospheric interface of variable thickness regulating radiative and turbulent fluxes between the surface and the free-troposphere. The most important parameters defining the ABL in space and time is the height of the temperature inversion layer. During winter the high latitude ABL remains mostly stable due to the absence of diurnal cycle while experiencing sometimes neutral conditions. Therefore, depending upon the synoptic meteorological forcing, deep and steeped temperature inversion layers are normally present. These layers are called elevated temperature inversion layers to differentiate them from the locally developed surface based inversion layer. Synoptic anticyclone conditions expose the surface to a continuous radiative cooling and therefore bringing the coldest conditions near. Conversely, cyclonic activity penetrating north increases down-welling longwave radiation introducing a radiative feedback that can remove the temperature gradient of the lowest layers close to the surface. This meteorological pattern drives the warmest periods during winter in high latitudes regions. Thus, the annual cooling rate in polar regions is self-regulated by the presence of the ABL and its radiative properties but it is also disrupted by the warming effect of large scale cyclone intrusions.

The ABL structure can be characterized by ground based instruments and to some extent by satellite remote sensing platforms. GPS Radio Occultation (GPSRO), when penetrating deep enough, can provide insightful information given the spatial coverage of the occultation methodology over the timescales corresponding to synoptic meteorological variations.

In this paper, an analysis of GPS-RO complemented by thermodynamic radiosonde observations (RAOBS) was conducted. The period from October 01 to March 31 of each winter season was chosen from 2006 to 2015. This analysis considers GPS-RO having the deepest penetration level close to surface and in a narrow region of 2^o by 2^o nearby Fairbanks (PAFA-70126) and Barrow (PABR-70026) stations. A statistical sampling of elevated temperature inversions layers was conducted and based on RAOBS information the spatial sampling was scrutinized for anticyclone and cyclone driven elevated temperature inversions. The paper delineates the methodology to carry out the analysis of GPSRO under the cases of stable and strongly stratified ABLs and discusses the obtained times series based on previous analyses conducted on the basis of RAOBS information alone.