A 10 year climatology of Arctic cloud fraction and radiative forcing at Barrow, Alaska

Abstract

A 10 year record of Arctic cloud fraction and radiative forcing has been generated using data collected at the Atmospheric Radiation Measurement (ARM) North Slope of Alaska site and the nearby NOAA Barrow Observatory (BRW) from June 1998 to May 2008. The cloud fractions (CFs) derived from ARM radar‐lidar and ceilometer measurements increase significantly from March to May (0.57→0.84), remain relatively high (∼0.80–0.9) from May to October, and then decrease from November to the following March (0.8→0.57), having an annual average of 0.76. These CFs are comparable to those derived from ground‐based radar‐lidar observations during the Surface Heat Budget of the Arctic Ocean experiment and from satellite observations over the western Arctic regions. The monthly means of estimated clear‐sky and measured all‐sky shortwave (SW)‐down and longwave (LW)‐down fluxes at the two facilities are almost identical with the annual mean differences less than 1.6 Wm−2. Values of LW cloud radiative forcing (CRF) are minimum (6 Wm−2) in March, then increase monotonically to reach maximum (63 Wm−2) in August, then decrease continuously to the following March. The cycle of SW CRF mirrors its LW counterpart with the greatest negative impact occurring during the snow‐free months of July and August. On annual average, the negative SW CRFs and positive LW CRFs nearly cancel, resulting in annual average NET CRF of about 3.5 Wm−2 on the basis of the combined ARM and BRW analysis. Compared with other studies, we find that LW CRF does not change over the Arctic regions significantly, but NET CRFs change from negative to positive from Alaska to the Beaufort Sea, indicating that Barrow is at a critical latitude for neutral NET CRF. The sensitivity study has shown that LW CRFs increase with increasing cloud fraction, liquid water path, and radiating temperature with high positive correlations (0.8–0.9). Negative correlations are found for SW CRFs, but a strong positive correlation between SW CRF and surface albedo exists.

Critical mechanisms for the formation of extreme arctic sea-ice extent in the summers of 2007 and 1996

“…The surface LWnet and SWnet fluxes were respectively 9.8 and 4.2 Wm -2 higher and lower than their corresponding climatic means, resulting in a 5.6 Wm -2 positive anomaly of net radiative flux (more downward). This result is consistent with previous findings (Francis et al 2005;Dong et al 2010) where both studies provide strong support for the finding in this study, i.e., LW effect overwhelmed SW effect over the AOF. For example, Francis et al (2005) studied the ice edges of all six peripheral seas over Arctic and found that the LW anomalies contributed about 40 % to the total variability, but the SW anomalies were overwhelmed by the LW impact when CF was high.…”

“…This simple parameterization may generate considerable biases in upwelling and downwelling SW fluxes, which lead to problems in the evaluation of the icealbedo feedback process. The observed snow/ice albedos at the BSRN Barrow site (Zib et al 2012, Dong et al 2010 and during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment (Intrieri et al 2002) are around 0.80-0.90. The downwelling SW flux is primarily determined by the following three parameters: cloud fraction and optical depth, and surface albedo.…”

Characterizing Arctic mixed‐phase cloud structure and its relationship with humidity and temperature inversion using ARM NSA observations

“…seasonal variation of total cloud occurrence [Intrieri et al, 2002;Dong et al, 2010;Shupe et al, 2011;Shupe, 2011] with lower magnitudes.…”

Is there a “new normal” climate in the Beaufort Sea?

“…Radiation data from the US Department of Energy Atmospheric Radiation Monitoring and the NOAA Global Monitoring Division observatories in Barrow, Alaska, were obtained and processed at the University of North Dakota (Dong et al 2010). These data were used, in combination with ice concentration, to estimate the long-term change in energy absorbed by the surface ocean, following Perovich et al (2007).…”