Modeling of Tropical Forcing of Persistent Droughts and Pluvials over Western North America: 1856–2000*
Open Access
- 1 October 2005
- journal article
- research article
- Published by American Meteorological Society in Journal of Climate
- Vol. 18 (19), 4065-4088
- https://doi.org/10.1175/jcli3522.1
Abstract
The causes of persistent droughts and wet periods, or pluvials, over western North America are examined in model simulations of the period from 1856 to 2000. The simulations used either (i) global sea surface temperature data as a lower boundary condition or (ii) observed data in just the tropical Pacific and computed the surface ocean temperature elsewhere with a simple ocean model. With both arrangements, the model was able to simulate many aspects of the low-frequency (periods greater than 6 yr) variations of precipitation over the Great Plains and in the American Southwest including much of the nineteenth-century variability, the droughts of the 1930s (the “Dust Bowl”) and 1950s, and the very wet period in the 1990s. Results indicate that the persistent droughts and pluvials were ultimately forced by persistent variations of tropical Pacific surface ocean temperatures. It is argued that ocean temperature variations outside of the tropical Pacific, but forced from the tropical Pacific, act to strengthen the droughts and pluvials. The persistent precipitation variations are part of a pattern of global variations that have a strong hemispherically and zonally symmetric component, which is akin to interannual variability, and that can be explained in terms of interactions between tropical ocean temperature variations, the subtropical jets, transient eddies, and the eddy-driven mean meridional circulation. Rossby wave propagation poleward and eastward from the tropical Pacific heating anomalies disrupts the zonal symmetry, intensifying droughts and pluvials over North America. Both mechanisms of tropical driving of extratropical precipitation variations work in summer as well as winter and can explain the year-round nature of the precipitation variations. In addition, land–atmosphere interactions over North America appear important by (i) translating winter precipitation variations into summer evaporation and, hence, precipitation anomalies and (ii) shifting the northward flow of moisture around the North Atlantic subtropical anticyclone eastward from the Plains and Southwest to the eastern seaboard and western Atlantic Ocean.This publication has 39 references indexed in Scilit:
- Long-Term Aridity Changes in the Western United StatesScience, 2004
- Paleoclimatic Analogs to Twentieth-Century Moisture Regimes Across the United StatesBulletin of the American Meteorological Society, 2003
- The Perfect Ocean for DroughtScience, 2003
- An interpretation of the results from atmospheric general circulation models forced by the time history of the observed sea surface temperature distributionGeophysical Research Letters, 2000
- Hydrologic Variation in the Northern Great Plains During the Last Two MillenniaQuaternary Research, 2000
- Recent Precipitation Trends in Southern South America East of the Andes: An Indication of Climatic VariabilityPublished by Springer Science and Business Media LLC ,2000
- Interannual Variability of the North American Warm Season Precipitation RegimeJournal of Climate, 1999
- Decadal Variability of Precipitation over Western North AmericaJournal of Climate, 1998
- The Hydrologic and Thermodynamic Characteristics of the NCAR CCM3*Journal of Climate, 1998
- Planetary-Scale Atmospheric Phenomena Associated with the Southern OscillationMonthly Weather Review, 1981