Volcanos and El Nino: Signal separation in northern hemisphere winter
- Max-Planck-Institut fuer Meteorologie, Hamburg (Germany)
The frequent coincidence of volcanic forcing with El Nino events disables the clear assignment of climate anomalies to either volcanic or El Nino forcing. In order to select the signals, a set of four different perpetual January GCM experiments was performed (control, volcano case, El Nino case and combined volcano/El Nino case) and studied with advanced statistical methods for the Northern Hemisphere winter. The results were compared with observations. The signals for the different forcings are discussed for three variables (temperature, zonal wind and geopotential height) and five levels (surface, 850 hPa. 500 hPa, 200 hPa and 50 hPa). The global El Nino signal can be selected more clearly in the troposphere than in the stratosphere. In contrast, the global volcano signal is strongest in the stratospheric temperature field. The amplitude of the perturbation for the volcano case is largest in the Atlantic region. The observed effect of local cooling due to the volcanic reduction of short-wave radiation over large land areas (like Asia) in sub-tropical regions, the observed advective warming over Eurasia and the advective cooling over Greenland are well simulated in the model. The radiative cooling near the surface is important for the volcano signal in the subtropics, but it is weak in high latitudes during winter. A statistically significant tropospheric signal of El Nino forcing occurs in the subtropics and in the mid-latitudes of the North Pacific. The local anomalies in the El Nino forcing region in the tropics, and the warming over North America in middle and high latitudes are simulated as observed. The combined signal is different from a simple linear combination of the separate signals. It leads to a climate perturbation stronger than for forcing with El Nino or stratospheric aerosol alone and to a somewhat modified pattern. 73 refs., 16 figs., 2 tabs.
- OSTI ID:
- 272735
- Journal Information:
- Climate Dynamics, Vol. 11, Issue 6; Other Information: PBD: Aug 1995
- Country of Publication:
- United States
- Language:
- English
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