84 research outputs found
Seasonal evolution of stratosphere-troposphere coupling in the Southern Hemisphere and implications for the predictability of surface climate
Stratosphere-troposphere coupling in the Southern Hemisphere (SH) polar vortex is an important dynamical process that provides predictability of the tropospheric Southern Annular Mode (SAM) and its associated surface impacts. SH stratosphere-troposphere coupling is explored by height-time domain empirical orthogonal function (EOF) analysis applied to the zonal mean-zonal wind anomalies averaged over the Antarctic circumpolar region (55â65°S; U55â65°S). The leading EOF explains 42% of the height-time variance of U55â65°S and depicts the variations of the vortex that is tightly tied to the seasonal breakdown of the vortex during late spring. The leading EOF pattern, defined here as the stratosphere-troposphere coupled mode, is characterized by variations in U55â65°S that develop in early winter near the stratopause, change sign from late winter to early spring, gain maximum amplitude during October in the upper stratosphere, and then extend downward to the surface from October to January. This stratosphere-troposphere coupling during the spring months appears to be preconditioned by anomalies in upward propagating planetary wave activity and a meridional shift of the vortex as high as the stratopause and as early as June. Interannual variations of the stratosphere-troposphere coupled mode are highly correlated with those of the tropospheric SAM, Antarctic stratospheric ozone concentration, Antarctic sea ice concentrations in the South Pacific and the Weddell Sea, and SH regional climate during late springâearly summer. Anomalies in the upper stratospheric flow as early as June are thus a potentially important source of predictability for the tropospheric SAM and its associated impacts on surface climate in spring and summer
Subseasonal to Seasonal Climate Forecasts Provide the Backbone of a Near-Real-Time Event Explainer Service
The Bureau of Meteorology serves the Australian community to reduce its climate risk and is developing a suite of tools to explain the drivers of extreme events. Dynamical sub-seasonal to seasonal forecasts form the backbone of the service, potentially enabling it to be run in near real time
Brassinolide interacts with auxin and ethylene in the root gravitropic response of maize ( Zea mays )
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72956/1/j.0031-9317.2004.00356.x.pd
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The 2019 Southern Hemisphere stratospheric polar vortex weakening and its impacts
This study offers an overview of the low-frequency (i.e., monthly to seasonal) evolution, dynamics, predictability, and surface impacts of a rare Southern Hemisphere (SH) stratospheric warming that occurred in austral spring 2019. Between late August to mid-September 2019, the stratospheric circumpolar westerly jet weakened rapidly, and Antarctic stratospheric temperatures rose dramatically. The deceleration of the vortex at 10 hPa was as drastic as that of the first ever observed major sudden stratospheric warming in the SH during 2002, while the mean Antarctic warming over the course of spring 2019 broke the previous record of 2002 by ~50% in the mid-stratosphere. This event was preceded by a poleward shift of the SH polar night jet in the uppermost stratosphere in early winter, which was then followed by record-strong planetary wave-one activity propagating upward from the troposphere in August that acted to dramatically weaken the polar vortex throughout the depth of the stratosphere. The weakened vortex winds and elevated temperatures moved downward to the surface from mid-October to December, promoting a record strong swing of the Southern Annular Mode (SAM) to its negative phase. This record-negative SAM appeared to be a primary driver of the extreme hot and dry conditions over subtropical eastern Australia that accompanied the severe wildfires that occurred in late spring 2019. State-of-the-art dynamical seasonal forecast systems skilfully predicted the significant vortex weakening of spring 2019 and subsequent development of negative SAM from as early as late July
A phase II trial of Cremorphor EL-free paclitaxel (Genexol-PM) and gemcitabine in patients with advanced non-small cell lung cancer
Stratospheric Ozone Changes and Climate, Chapter 5 in WMO Scientific Assessment of Ozone Depletion (2018)
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The role of the stratosphere in subseasonal to seasonal prediction part I: predictability of the stratosphere
The stratosphere has been identified as an important source of predictability for a range of processes on subseasonal to seasonal (S2S) timescales. Knowledge about S2S predictability within the stratosphere is however still limited. This study evaluates to what extent predictability in the extratropical stratosphere exists in hindcasts of operational prediction systems in the S2S database. The stratosphere is found to exhibit extended predictability as compared to the troposphere. Prediction systems with higher stratospheric skill tend to also exhibit higher skill in the troposphere. The analysis also includes an assessment of the predictability for stratospheric events, including early and midâwinter sudden stratospheric warming (SSW) events, strong vortex events, and extreme heat flux events for the Northern Hemisphere, and final warming events for both hemispheres. Strong vortex events and final warming events exhibit higher levels of predictability as compared to SSW events. In general, skill is limited to the deterministic range of one to two weeks. Highâtop prediction systems overall exhibit higher stratospheric prediction skill as compared to their lowâtop counterparts, pointing to the important role of stratospheric representation in S2S prediction models
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The role of the stratosphere in subseasonal to seasonal prediction part II: predictability arising from stratosphere â troposphere coupling
The stratosphere can have a signi_cant impact on winter surface weather on subseasonal to seasonal (S2S) timescales. This study evaluates the ability of current operational S2S prediction systems to capture two important links between the stratosphere and tropo sphere: (1) changes in probabilistic prediction skill in the extratropical stratosphere by precursors in the tropics and the extratropical troposphere and (2) changes in surface predictability in the extratropics after stratospheric weak and strong vortex events. Prob abilistic skill exists for stratospheric events when including extratropical tropospheric precursors over the North Paci_c and Eurasia, though only a limited set of models captures the Eurasian precursors. Tropical teleconnections such as the MaddenâJulian Oscillation, the QuasiâBiennial Oscillation, and El Nin~o Southern Oscillation increase the probabilistic skill of the polar vortex strength, though these are only captured by a limited set of models. At the surface, predictability is increased over the USA, Russia, and the Middle East for weak vortex events, but not for Europe, and the change in predictability is smaller for strong vortex events for all prediction systems. Prediction systems with poorly resolved stratospheric processes represent this skill to a lesser degree. Altogether, the analyses indicate that correctly simulating stratospheric variability and stratosphereâtroposphere dynamical coupling are critical elements for skillful S2S wintertime predictions
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The role of the stratosphere in subseasonal to seasonal prediction part I: predictability of the stratosphere
The stratosphere has been identified as an important source of predictability for a range of processes on subseasonal to seasonal (S2S) timescales. Knowledge about S2S predictability within the stratosphere is however still limited. This study evaluates to what extent predictability in the extratropical stratosphere exists in hindcasts of operational prediction systems in the S2S database. The stratosphere is found to exhibit extended predictability as compared to the troposphere. Prediction systems with higher stratospheric skill tend to also exhibit higher skill in the troposphere. The analysis also includes an assessment of the predictability for stratospheric events, including early and midâwinter sudden stratospheric warming (SSW) events, strong vortex events, and extreme heat flux events for the Northern Hemisphere, and final warming events for both hemispheres. Strong vortex events and final warming events exhibit higher levels of predictability as compared to SSW events. In general, skill is limited to the deterministic range of one to two weeks. Highâtop prediction systems overall exhibit higher stratospheric prediction skill as compared to their lowâtop counterparts, pointing to the important role of stratospheric representation in S2S prediction models
Dynamics and predictability of El Nino-Southern Oscillation: an Australian perspective on progress and challenges
Many scientific challenges remain for managing the risk of future ENSO impacts in countries like Australia that are strongly affected by ENSO event diversity
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