Manisha Ganeshan - 613 Seminar Series

GESTAR/USRA

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In this study, high-resolution refractivity profiles from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation (RO) along with ship-based meteorological observations are used to investigate Arctic boundary layer properties. The stable temperature inversion over sea-ice plays an important role in the surface climate of the Arctic through direct and indirect feedbacks. Although several studies have investigated Arctic inversion characteristics such as height, depth, and frequency, there are significant challenges for long-term climate monitoring mainly due to limited sampling over the ocean and/or poor resolution of available observations. The high vertical resolution and frequent sampling of COSMIC RO observations allow for a unique investigation of the inversion characteristics over the Arctic Ocean. For the coldest and driest months, a reliable retrieval technique for inversion height and surface-based inversion (SBI) frequency is developed. We find that these variables have a strong negative relationship over the Arctic Ocean and are well-correlated in the time and space domain. The spatial patterns show a minimum inversion height (maximum SBI frequency) over the ice-covered Pacific sector of the ocean, similar to that observed in past studies. Over the ocean, the lowest inversion height (most frequent SBIs) occurs during the transition period from winter to spring (February-March). Little diurnal variability is observed in the mean inversion properties during the cold season. For the warmer months, atmospheric moisture interferes with RO refractivity therefore making the retrieval method less reliable. A novel approach based on the variance of the refractivity is explored to retrieve the boundary layer cloud-top height during summer months.

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Recent satellite-based studies have suggested that the low-cloud cover is increasing over the ice-free Arctic Ocean during fall. Multi-year ship-based observations collected during September and early October is investigated in this study, and we find that the boundary layer is indeed more mixed in regions where the sea-ice has retreated. A pronounced air-sea temperature difference combined with favorable surface wind conditions appear to support a more convective boundary layer during early fall. The surface sensible heat flux is found to play a significant role in mixed layer formation over open water, but also along the marginal sea-ice zone during cold-air outbreak (CAO) events. These events are associated with the advection of cold, dry polar air mass over the open Arctic Ocean and the subsequent formation of boundary layer clouds. The penetration of COSMIC RO in the atmospheric boundary layer can be useful for tracking such events. This is because RO penetration can be a good proxy for atmospheric moisture distribution in high latitudes. Despite its limitations, it is found that COSMIC RO can be useful for characterizing Arctic boundary layer properties and therefore monitoring polar climate dynamics.