Nonlinear intensification of monsoon low pressure systems by the BSISO

More than half of the rainfall brought to the Indian subcontinent by the summer monsoon is associated with low-pressure systems (LPSs). Yet their relationship with the Boreal Summer Intraseasonal Oscillation (BSISO) &ndash; the dominant intraseasonal forcing on the monsoon &ndash; is only superficially understood. Using reanalysis data, we explore the relationship between the BSISO and LPS intensity, propagation, and precipitation, and associated underlying mechanisms. The BSISO has a large impact on mean monsoon vorticity and rainfall as it moves northward &ndash; maximising both in phases 2&ndash;3 over southern India and phases 5&ndash;6 over northern India &ndash; but a much weaker relationship with total column water vapour. We present evidence that LPS genesis also preferentially follows these phases of the BSISO. We identify significant relationships between BSISO phase and LPS precipitation and propagation: for example, during BSISO phase 5, LPSs over north India produce 51 % heavier rainfall and propagate northwestward 20 % more quickly. Using a combination of moisture flux linearisation and quasigeostrophic theory, we show that these relationships are driven by changes to the underlying dynamics, rather than the moisture content or thermodynamic structure, of the monsoon. Using the example of LPSs over northern India during BSISO phase 5, we show that the vertical structure of anomalous vorticity can be split into contributions from the BSISO and the nonlinear response of the LPS to anomalous BSISO circulation. Complementary hypotheses emerge about the source of this nonlinear vorticity response: nonlinear frictional convergence and secondary barotropic growth. We show that both are important. The BSISO imparts greater meridional shear on the background state, supporting LPS intensification. The BSISO background and nonlinear LPS response both contribute significantly to anomalous boundary layer convergence, and we show through vortex budget arguments that the former supports additional LPS intensification in boundary layer while the latter supports faster westward propagation. This work therefore yields important insights into the scale interactions controlling one of the dominant synoptic systems contributing to rainfall during the monsoon.</p

Influencing students' construction of personalised concept maps through the use of query expansion (QE) searching of the World Wide Web

Despite the on-going development of search engines, users of the World Wide Web, including school and undergraduate students, still find searching for appropriate information problematic. Keener students may seek relevant information to help them to construct a better understanding of the various concepts within a taught subject. Unfortunately there is no guarantee that the information contained in the located documents is of sufficient educational quality; measured for example in terms of the information's usefulness, accuracy, relevancy, trustworthiness, level of language, completeness and status. In this research it is argued that a domain expert (perhaps in the form of a "web literate" subject tutor) has several major advantages over a school or undergraduate student when it comes to searching for relevant subject-related informatio

Representation of western disturbances in CMIP5 models

Western disturbances (WDs) are synoptic extratropical disturbances embedded in the subtropical westerly jet stream. They are an integral part of the South Asian winter climate, both for the agriculture-supporting precipitation they bring to the region and for the associated isolated extreme events that can induce devastating flash flooding. Here, WD behaviour and impacts are characterised in 23 CMIP5 historical simulations and compared with reanalysis and observations. It is found that WD frequency has a strong relationship with model resolution: higher resolution models produce significantly more WDs, and a disproportionately high fraction of extreme events. Exploring metrics of jet strength and shape, we find that the most probable cause of this relationship is that the jet is wider in models with coarser resolution, and therefore the northern edge in which WDs are spun up sits too far north of India. The frequency of WDs in both winter and summer is found to be overestimated by most models, and thus the winter frequency of WDs estimated from the multi-model mean (30 winter−1) is above the reanalysis mean (26 winter−1). In this case, the error cannot be adequately explained by local jet position and strength. Instead, we show that it is linked with a positive bias in upstream mid-tropospheric baroclinicity. Despite a positive winter precipitation bias in CMIP5 models over most of India and Pakistan and a dry bias in the western Himalaya, the fraction of winter precipitation for which WDs are responsible is accurately represented. Using partial correlation, it is shown that the overestimation in WD frequency is the largest contributor to this bias, with a secondary, spatially heterogeneous contribution coming from the overestimation of WD intensity

Falling trend of western disturbances in future climate simulations

Western disturbances (WDs) are synoptic-scale cyclonic weather systems advected over Pakistan and north India by the subtropical westerly jet stream. There, they are responsible for most of the winter precipitation, crucial for agriculture of the rabi crop, as well as more extreme precipitation events, which can lead to local flooding and avalanches. Despite their importance, there has not yet been an attempt to objectively determine the fate of WDs in future climate GCMs. Here, a tracking algorithm is used to build up a catalogue of WDs in both CMIP5 historical and representative concentration pathway (RCP) experiments of the future. It is shown that in business-as-usual (RCP8.5) future climate simulations, WD frequency falls by around 15% by the end of the twenty-first century, with the largest relative changes coming in pre- and post-monsoon months. Meanwhile, mean WD intensity will decrease, with central vorticity expected to become less cyclonic by about 12% over the same period. Changes in WD frequency are attributed to the projected widening and weakening of the winter subtropical jet; as well as decreasing meridional wind shear and mid-tropospheric baroclinic vorticity tendency, which also explain the changes in intensity. Finally, the impact of these changes on regional precipitation is explored. The decline in WD frequency and intensity will cause a decrease in mean winter rainfall over Pakistan and north India amounting to about 15% of the mean -- subject to the ability of the models to represent the processes responsible. The effect on extreme precipitation events, however, remains unclear

The effect of soil moisture perturbations on Indian Monsoon Depressions in a numerical weather prediction model

Indian monsoon depressions (MDs) are synoptic-scale cyclonic systems that propagate across peninsular India three or four times per monsoon season. They are responsible for the majority of rainfall in agrarian north India, thus constraining precipitation estimates is of high importance. Here, we use a case study from August 2014 to explore the relationship between varying soil moisture and the resulting track and structure of an incident MD using the Met Office Unified Model. We use this case study with the view to increasing understanding of the general impact of soil moisture perturbations on monsoon depressions. It is found that increasing soil moisture in the monsoon trough region results in deeper inland penetration and a more developed structure - e.g. a warmer core in the mid-troposphere and a stronger bimodal potential vorticity core in the middle/lower troposphere - with more precipitation, and a structure that in general more closely resembles that found in depressions over the ocean, indicating that soil moisture may enhance the convective mechanism that drives depressions over land. This experiment also shows that these changes are most significant when the depression is deep, and negligible when it is weakening. Increasing soil moisture in the sub-Himalayan arable zone, a region with large irrigation coverage, also caused deeper inland penetration and some feature enhancement in the upper troposphere but no significant changes were found in the track heading or lower-tropospheric structure

Influencing students' construction of personalised concept maps through the use of query expansion (QE) searching of the World Wide Web

Despite the on-going development of search engines, users of the World Wide Web, including school and undergraduate students, still find searching for appropriate information problematic. Keener students may seek relevant information to help them to construct a better understanding of the various concepts within a taught subject. Unfortunately there is no guarantee that the information contained in the located documents is of sufficient educational quality; measured for example in terms of the information's usefulness, accuracy, relevancy, trustworthiness, level of language, completeness and status. In this research it is argued that a domain expert (perhaps in the form of a "web literate" subject tutor) has several major advantages over a school or undergraduate student when it comes to searching for relevant subject-related informatio

Automated service monitoring in the deployment of ARCHER2

The ARCHER2 service, a CPU based HPE Cray EX system with 750,080 cores (5,860 nodes), has been deployed throughout 2020 and 2021, going into full service in December of 2021. A key part of the work during this deployment was the integration of ARCHER2 into our local monitoring systems. As ARCHER2 was one of the very first large-scale EX deployments, this involved close collaboration and development work with the HPE team through a global pandemic situation where collaboration and co-working was significantly more challenging than usual. The deployment included the creation of automated checks and visual representations of system status which needed to be made available to external parties for diagnosis and interpretation. We will describe how these checks have been deployed and how data gathered played a key role in the deployment of ARCHER2, the commissioning of the plant infrastructure, the conduct of HPL runs for submission to the Top500 and contractual monitoring of the availability of the ARCHER2 service during its commissioning and early life