Murphy Lisa N.

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Murphy
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Lisa N.
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  • Article
    Holocene black carbon in Antarctica paralleled Southern Hemisphere climate
    (John Wiley & Sons, 2017-07-01) Arienzo, Monica ; McConnell, Joseph R. ; Murphy, Lisa N. ; Chellman, Nathan ; Das, Sarah B. ; Kipfstuhl, Sepp ; Mulvaney, Robert
    Black carbon (BC) and other biomass-burning (BB) aerosols are critical components of climate forcing, but quantification, predictive climate modeling, and policy decisions have been hampered by limited understanding of the climate drivers of BB and by the lack of long-term records. Prior modeling studies suggested that increased Northern Hemisphere anthropogenic BC emissions increased recent temperatures and regional precipitation, including a northward shift in the Intertropical Convergence Zone (ITCZ). Two Antarctic ice cores were analyzed for BC, and the longest record shows that the highest BC deposition during the Holocene occurred ~8–6 k years before present in a period of relatively high austral burning season and low growing season insolation. Atmospheric transport modeling suggests South America (SA) as the dominant source of modern Antarctic BC and, consistent with the ice core record, climate model experiments using mid-Holocene and preindustrial insolation simulate comparable increases in carbon loss due to fires in SA during the mid-Holocene. SA climate proxies document a northward shifted ITCZ and weakened SA Summer Monsoon (SASM) during this period, with associated impacts on hydroclimate and burning. A second Antarctic ice core spanning the last 2.5 k years documents similar linkages between hydroclimate and BC, with the lowest deposition during the Little Ice Age characterized by a southerly shifted ITCZ and strengthened SASM. These new results indicate that insolation-driven changes in SA hydroclimate and BB, likely linked to the position of the ITCZ, modulated Antarctic BC deposition during most of the Holocene and suggests connections and feedbacks between future BC emissions and hydroclimate.
  • Working Paper
    A model based approach to understanding the phase locking of ENSO and the annual cycle
    ( 2014-07-11) Karnauskas, Kristopher B. ; Murphy, Lisa N.
    The present study is an investigation into the physical underpinnings of the phase locking between ENSO and the annual cycle. An appreciable amount of work has been aimed at this and similar questions, particularly observational studies resulting from the TOGA decade. In contrast, relatively little modeling efforts have been directed at understanding why peak conditions of most El Nino events in recent decades have occurred in boreal winter. Current knowledge of the global effects of El Nino remains based on observations of El Nino impacting the Earth during boreal winter. Using an OGCM of the tropical Pacific Ocean and various in situ data, it is found that the first order explanation of the seasonal timing of ENSO events, simply that westerly wind bursts occur during that season, is far short of complete. Rather, the state of the ocean is itself better situated thermodynamically to respond to the wind anomalies that are believed to play an important role in the genesis of El Nino events.