506 The SPARC Data Center and Stratospheric Precursors for Tropospheric Phenomena

Thursday, 14 January 2016
Stefan Liess, University of Minnesota, Saint Paul, MN

Handout (7.1 MB)

The stratospheric circulation significantly affects tropospheric phenomena such as the Northern Annular Mode (NAM) and the Southern Annular Mode (SAM). In previous work with Prof. Marvin Geller, we found that the stratospheric quasi-biennial oscillation (QBO) significantly affects the tropical troposphere. We identified the QBO signal in tropical deep convection. Some difficulties in earlier studies were ambiguities in the identification of tropical deep convection in observations, and also in separating the El Niño/Southern Oscillation (ENSO) and other tropospheric signals from QBO influences. We used a cluster analysis of 21.5 years of International Satellite Cloud Climatology Project tropical weather states to identify tropical deep convection and cirrus clouds, as well as 32.25 years of precipitation data as proxies for deep convection. Correlations between the QBO, ENSO, and other tropospheric patterns such as the tropospheric biennial oscillation and Pacific decadal oscillation were taken into account to isolate the influence of the QBO. Although tropical deep convection is mostly related to ENSO and the annual cycle, the QBO westerly phase, independent of the annual cycle as well as impacts of ENSO, leads to an eastward shift in the strength of meridional overturning contributions to the Hadley circulation over the Pacific and thus also affects the subtropical circulation.

For deep convective clouds, relative differences in convective cloud cover between the QBO easterly and QBO westerly phases can be as large as 51%±7% of the annual average over isolated regions in the tropical west Pacific and 103%±35% over the east Pacific, where the absolute values are lower and where notable deviations occur during the QBO westerly phase.

Inspired by these results, more recent work includes a composite analysis of 50-hPa geopotential height anomalies In the Southern Hemisphere, between the Tasman Sea and the Southern Ocean, which suggests a teleconnection pattern between these regions in the lower stratosphere during southern fall and winter that is present throughout the year in the troposphere. In the stratosphere, the northern center is missing in southern spring, and the southern center is not significant in summer. These geopotential height anomalies indicate a vertically coherent zonal wind anomaly pattern that can extend from Earth's surface upward into the lower stratosphere. At 50 hPa, the strongest positive geopotential height anomalies are found north of the Ross Sea and Bellingshausen Sea during summer and fall. These anomalies might lead to a tripolar pattern in fall and the above teleconnection pattern in winter. However, the polar vortex is strongest in midwinter and thus is less prone to zonal anomalies in geopotential height.

The significant correlation at 50 hPa during fall indicates the presence of the teleconnection during this season with a positive peak in 50-hPa geopotential height anomaly over southern Australia and a negative peak northwest of the Ross Sea. In the troposphere and the lower stratosphere, the SAM has a regional peak to the east of this teleconnection. However, the stratosphere–troposphere coupling suggests that both the SAM and this teleconnection are triggered by a stratospheric signal.

In the Northern Hemisphere, a stratospheric signal over northwestern Russia generates a tropospheric wave train through Central Asia that influences the west Pacific warm pool and thus the ENSO signal. The above results are also discussed with regards to their impact on regional precipitation patterns and thus the general hydrologic cycle, since the positive phase of the teleconnection in the Southern Hemisphere is suggested to lead to longterm droughts over Australia and the wave train over Central Asia severely impacts the hydrologic response to the ENSO signal.

Furthermore, this presentation will provide an overview of the SPARC Data Center including previous hardware upgrades and an update on the current status and progress on the migration from Stony Brook University to CEDA.

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