The joint influence of the stratospheric quasi‐biennial oscillation (QBO) and the El Niño Southern Oscillation (ENSO) on the polar vortex, subtropical westerly jets (STJs), and wave patterns during boreal winter is investigated in 40 years (1979–2018) of monthly mean ERA‐Interim reanalyses. The method of Wallace et al. (1993),
- Award ID(s):
- 1902409
- NSF-PAR ID:
- 10413784
- Date Published:
- Journal Name:
- Journal of Climate
- ISSN:
- 0894-8755
- Page Range / eLocation ID:
- 1 to 26
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract https://doi.org/10.1175/15200469(1993)050<1751:ROTESQ>2.0.CO;2 is used to conduct a QBO phase angle sweep. QBO westerly (W) and easterly (E) composites are then segregated by the phase of ENSO. Two pathways are described by which the QBO mean meridional circulation (MMC) influences the northern winter hemisphere. The “stratospheric pathway” modulates stratospheric planetary wave absorption via the Holton‐Tan mechanism. The “tropospheric pathway” modulates the tropical and subtropical upper troposphere and lower stratosphere. QBO MMC anomalies exhibit a checkerboard pattern in temperature and arched structures in zonal wind which extend into midlatitudes, and are stronger on the winter side. During QBO W, the polar vortex and STJs are enhanced. QBO signals in the polar vortex are amplified during La Niña. During El Niño and QBO W, the strongest STJs occur, and a warm pole/wave two pattern is found. During El Niño and QBO E, a trough is found over Eurasia and a ridge over the North Atlantic, in a wave one pattern. El Niño diminishes QBO anomalies in the tropical stratosphere and reduces the poleward extent and amplitude of the QBO MMC, thereby influencing the stratospheric pathway. Effects on the boreal winter hemisphere are attributed to the combined influence of the QBO and ENSO via both pathways. -
ITCZ Width Controls on Hadley Cell Extent and Eddy-Driven Jet Position and Their Response to Warmingmore » « less
The impact of global warming–induced intertropical convergence zone (ITCZ) narrowing onto the higher-latitude circulation is examined in the GFDL Atmospheric Model, version 2.1 (AM2.1), run over zonally symmetric aquaplanet boundary conditions. A striking reconfiguration of the deep tropical precipitation from double-peaked, off-equatorial ascent to a single peak at the equator occurs under a globally uniform +4 K sea surface temperature (SST) perturbation. This response is found to be highly sensitive to the SST profile used to force the model. By making small (≤1 K) perturbations to the surface temperature in the deep tropics, varying control simulation precipitation patterns with both single and double ITCZs are generated. Across the climatologies, narrower regions of ascent correspond to more equatorward Hadley cell edges and eddy-driven jets. Under the global warming perturbation, the experiments in which there is narrowing of the ITCZ show significantly less expansion of the Hadley cell and somewhat less poleward shift of the eddy-driven jet than those without ITCZ narrowing. With a narrower ITCZ, the ascending air has larger zonal momentum, causing more westerly upper-tropospheric subtropical wind. In turn, this implies 1) the subtropical jet will become baroclinically unstable at a lower latitude and 2) the critical (zero wind) line will shift equatorward, allowing midlatitude eddies to propagate farther equatorward. Both of these mechanisms modify the Hadley cell edge position, and the latter affects the jet position.
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Abstract The 1783–1784 CE Laki flood lava eruption began on 8 June 1783. Over the course of 8 months, the eruption released approximately 122 Tg of sulfur dioxide gas into the upper troposphere and lower stratosphere above Iceland. Previous studies that have examined the impact of the Laki eruption on sulfate aerosol and climate have either used an aerosol model coupled off‐line to a general circulation model (GCM) or used a GCM with incomplete aerosol microphysics. Here, we study the impact on stratospheric aerosol evolution and stratospheric and tropospheric circulation using a fully coupled GCM with complete aerosol microphysics, the Community Earth System Model version 1, with the Whole Atmosphere Chemistry Climate Model high‐top atmosphere component. Simulations indicate that the Laki aerosols had peak average effective radii of approximately 0.4 μm in Northern Hemisphere (NH) middle and high latitudes, with peak average effective radii of 0.25 μm in NH tropics and 0.2 μm in the Southern Hemisphere. We find that the Laki aerosols are transported globally and have significant impacts on the circulation in both hemispheres, strengthening the Southern Hemisphere polar vortex and shifting the tropospheric NH subtropical jet equatorward.
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1175/JCLI-D-22-0851.1
