Charlotte Pascoe

Solar and QBO influences on the timing of stratospheric sudden warmings

Abstract The interaction of the 11-yr solar cycle (SC) and the quasi-biennial oscillation (QBO) and their influence on the Northern Hemisphere (NH) polar vortex are studied using idealized model experiments and ECMWF Re-Analysis (ERA-40). In the model experiments, the sensitivity of the NH polar vortex to imposed easterlies at equatorial/subtropical latitudes over various height ranges is tested to explore the possible influence from zonal wind anomalies associated with the QBO and the 11-yr SC in those regions. The experiments show that the timing of the modeled stratospheric sudden warmings (SSWs) is sensitive to the imposed easterlies at the equator/subtropics. When easterlies are imposed in the equatorial or subtropical upper stratosphere, the onset of the SSWs is earlier. A mechanism is proposed in which zonal wind anomalies in the equatorial/subtropical upper stratosphere associated with the QBO and 11-yr SC either reinforce each other or cancel each other out. When they reinforce, as in Smin–QBO-ea...

A GCM study of the influence of equatorial winds on the timing of sudden stratospheric warmings

A full troposphere-stratosphere-mesosphere global circulation model is used in a set of idealised experiments to investigate the sensitivity of the Northern Hemisphere winter stratospheric flow to improvements in the equatorial zonal winds. The model shows significant sensitivity to variability in the upper equatorial stratosphere, the imposition of SAO and QBO like variability in this region advances the timing of midwinter sudden warmings by about one month. Perturbations to the lower equatorial stratosphere are mainly found to influence early winter polar variability. These results suggest that it is important to pay attention to the capability of models to simulate realistic variability in the upper equatorial stratosphere.

A Possible Influence of Equatorial Winds on the September 2002 Southern Hemisphere Sudden Warming Event

The stratospheric sudden warming in the Southern Hemisphere (SH) in September 2002 was unexpected for two reasons. First, planetary wave activity in the Southern Hemisphere is very weak, and midwinter warmings have never been observed, at least not since observations of the upper stratosphere became regularly available. Second, the warming occurred in a west phase of the quasi-biennial oscillation (QBO) in the lower stratosphere. This is unexpected because warmings are usually considered to be more likely in the east phase of the QBO, when a zero wind line is present in the winter subtropics and hence confines planetary wave propagation to higher latitudes closer to the polar vortex. At first, this evidence suggests that the sudden warming must therefore be simply a result of anomalously strong planetary wave forcing from the troposphere. However, recent model studies have suggested that the midwinter polar vortex may also be sensitive to the equatorial winds in the upper stratosphere, the region dominated by the semiannual oscillation. In this paper, the time series of equatorial zonal winds from two different data sources, the 40-yr ECMWF Re-Analysis (ERA) and the Met Office assimilated dataset, are reviewed. Both suggest that the equatorial winds in the upper stratosphere above 10 hPa were anomalously easterly in 2002. Idealized model experiments are described in which the modeled equatorial winds were relaxed toward these observations for various years to examine whether the anomalous easterlies in 2002 could influence the timing of a warming event. It is found that the 2002 equatorial winds speed up the evolution of a warming event in the model. Therefore, this study suggests that the anomalous easterlies in the 1–10-hPa region may have been a contributory factor in the development of the observed SH warming. However, it is concluded that it is unlikely that the anomalous equatorial winds alone can explain the 2002 warming event.

The PIMMS Project and Natural Language Processing for Climate Science: Extending the ChemicalTagger Natural Language Processing Tool with Climate Science Controlled Vocabularies

Abstract Tools that capture information about the workflow of running simulations are becoming key parts of the workflow for climate scientists. Such tools need to capture information from the design of experiments (why) to their implementation in simulations (what) that are the description of how models were run (how). (“What was done, how and why” all linked to the data produced.) Previous work has described the implementation of a system for capturing such information in the context of the fifth Climate Model Intercomparison Project (CMIP5). That system uses controlled vocabularies to drive a centralised web questionnaire for collecting metadata in a standardised format, the “common information model”, (CIM). The PIMMS (Portable Infrastructure for the Metafor Metadata System; http://pimms.ceda.ac.uk .) project is taking that work and moving it to more flexible tools for institutional use. Such flexible tools include a more easily configured web system for local deployment. Alongside the modified version of the web questionnaire used for CMIP5, PIMMS is also exploring how the controlled vocabulary that is used to configure the PIMMS web interface may be of further value through the use of text mining. In doing so, PIMMS has extended and adapted the University of Cambridge ChemicalTagger tool for application in climate science. ChemicalTagger is a natural language processing system. The climate science adaptation of ChemicalTagger has been successful in processing Climate of the Past and Geoscientific Model Development journal articles. Here we discuss how information is obtained from climate papers, and specifically, how time information is obtained. Some publications have been mined to create model description documents in the CIM format, similar to those created using the web questionnaire technology. The process has shown some limitations of the CIM. Suggestions for future work include improvements to the tagging software, improvements for the conversion from the tagged markup into CIM, and improvements to the CIM itself.