Science Source

Midlatitude Moisture Contribution to Recent Arctic Tropospheric Summertime Variability

States that in recent decades, the midtroposphere (defined here as 600-400 hPa) has been warming faster in the Arctic than in the Northern Hemisphere midlatitudes; this warming has been accompanied by an increase in Arctic precipitable water
Focuses on the dynamical drivers of Arctic midtropospheric heat anomalies in observations to better understand the nature of heat transport in Arctic midtropospheric warming and polar amplification
States that warming typically reduces the sensible heat transport and increases the latent heat transport into the Arctic
Shows that increased heat transport into the Arctic is driven to an important extent by increased precipitable water in the midlatitude planetary boundary layer
Analyzes the dynamics of late summer Arctic tropospheric heat content variability using reanalyses
Finds in both trends and interannual variability, much of the August heat content variability in the Arctic midtroposphere can be explained by the total—sensible plus latent—heat content variability at the midlatitude near surface in July
Argues that heat content signals are propagated from the midlatitude near surface to the Arctic midtroposphere approximately along climatological moist isentropes
High-frequency data reveal that the propagating signal is primarily driven by a few strong meridional heat flux events each summer season
Composite analysis on these events shows that August meridional heat fluxes into the Arctic midtroposphere are succeeded by positive heat content anomalies in the lower troposphere a few days later
States this second connection between the Arctic midtroposphere and the Arctic lower troposphere could be sufficient to explain some of the recent Arctic 850-hPa temperature variability north of 75°N