A climatologically important look at liquid water distribution in low-level Arctic clouds

Remote sensing of low-level Arctic cloud cover and thermodynamics has lead to a regime identification during the melt season where cloud tops are found above the temperature inversion base. This regime is opposite to the previously-understood regime and mechanisms that support marine stratiform cloud development and persistence. Data from the IPY-supported Arctic Summer Cloud Ocean Study (ASCOS) in 2008, among additional Arctic data sets of cloud macrophysics and thermodynamics, are examined for cloud-inversion interactions. Radiative flux sensitivity tests are performed using a radiative transfer model by varying the vertical location of cloud liquid water distribution in relation to the thermodynamic structure. Optically thin clouds show an enhanced longwave radiative forcing at the surface, on the order of 0.5-2 W m-2, as cloud emissivity is enhanced by cloud liquid above the inversion. At the top of the atmosphere (TOA), the longwave forcing from cloud liquid above the inversion can be enhanced by nearly 10 W m-2 as cloud optical thickness increases. In addition to surface and TOA forcing, longwave flux divergence is shown to cause thermodynamic anomalies within the cloud layer. These sensitivity tests suggest a significant contribution to Arctic climate via cloud liquid water distribution.