The atmospheric response to sea ice anomalies over the Barents Sea during winter was determined by boundary forcing the Community Atmosphere Model (CAM) with daily varying high and low sea ice concentration (SIC) anomalies that decreased realistically from December to February. The high-and low-SIC anomalies produced localized opposite-signed responses of surface turbulent heat flux and wind stress that decreased in magnitude and extent as winter progressed. Responses of sea level pressure (SLP) and 500-mb height evolved from localized, opposite-signed features into remarkably similar large-scale patterns resembling the negative phase of the North Atlantic Oscillation (NAO). Hilbert empirical orthogonal function (HEOF) analysis of the composite high-SIC and low-SIC SLP responses uncovered how they differed. The hemispheric pattern in the leading HEOF was similar for the high-SIC and low-SIC responses, but the high-SIC response cycled through the pattern once per winter, whereas the low-SIC response cycled through the pattern twice per winter. The second HEOF differed markedly between the responses, with the high-SIC response featuring zonally oriented Atlantic and Pacific wave features and the low-SIC response featuring a meridionally oriented Atlantic dipole pattern.
Abstract. The amplitude of the mean annual cycle of atmospheric CO 2 is a diagnostic of seasonal surface-atmosphere carbon exchange. Atmospheric observations show that this quantity has increased over most of the Northern Hemisphere (NH) extratropics during the last 3 decades, likely from a combination of enhanced atmospheric CO 2 , climate change, and anthropogenic land use change. Accurate climate prediction requires accounting for long-term interactions between the environment and carbon cycling; thus, analysis of the evolution of the mean annual cycle in a fully prognostic Earth system model may provide insight into the multi-decadal influence of environmental change on the carbon cycle.We analyzed the evolution of the mean annual cycle in atmospheric CO 2 simulated by the Community Earth System Model (CESM) from 1950 to 2300 under three scenarios designed to separate the effects of climate change, atmospheric CO 2 fertilization, and land use change. The NH CO 2 seasonal amplitude increase in the CESM mainly reflected enhanced primary productivity during the growing season due to climate change and the combined effects of CO 2 fertilization and nitrogen deposition over the mid-and high latitudes. However, the simulations revealed shifts in key climate drivers of the atmospheric CO 2 seasonality that were not apparent before 2100. CO 2 fertilization and nitrogen deposition in boreal and temperate ecosystems were the largest contributors to mean annual cycle amplification over the mid-
For winters over eastern North America, complex Hilbert empirical orthogonal function (HEOF) analysis was used to objectively identify propagating patterns in four atmospheric fields that have potential relevance to precipitation: jet stream–level wind speed, 850-hPa moisture transport (qv), temperature advection (TA), and vorticity advection (VA). A novel phase shift method was used to show the location where each propagating pattern was most correlated with Midwest precipitation, and each of the four phase-shifted HEOF patterns was compared to its respective high-precipitation composite view. The leading HEOFs of the three transport fields (qv, TA, and VA), which collectively represented the dynamics associated with a midlatitude cyclone, accounted for almost half of Midwest precipitation variability and were associated with lake effect snow when propagating downstream from the Midwest. Correlation and spectral analyses revealed how the propagating transport patterns were related to the Pacific–North American pattern and other teleconnections. The leading HEOF of jet stream–level wind speed, which represented the tendency for the jet stream to migrate equatorward over the study region during winter, accounted for only about 4% of Midwest daily precipitation variability. In contrast, the second HEOF of jet stream–level wind speed, which represented an eastward propagating trough dynamically consistent with a midlatitude cyclone, accounted for 16% of Midwest daily precipitation variability.
A novel analysis method involving phase-shifted complex Hilbert empirical orthogonal functions (HEOFs) was used to examine how variations in predominant propagating patterns of Arctic surface wind influence daily Fram Strait sea ice export F during extended winter (October–April), a primary control on Arctic sea ice volume. Northwesterly winds favorable to F were provided by poleward-moving anticyclones upstream over the Canadian Arctic associated with the leading HEOF of wind and also by eastward-moving cyclones downstream over the Barents Sea associated with the second HEOF of wind. A suite of spatial and statistical analyses indicated that the aggregate of the two propagating patterns largely explains a sea level pressure pattern analyzed in several prior studies as a standing wave oriented east–west across the strait.
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