We consider the problem of a buoyant plume, generated in an unstratified region, impinging on a region with strong stable stratification. This is a simple representation of the tropical upper troposphere and lower stratosphere (UTLS), where convective plumes generated by strong thunderstorm complexes can penetrate into the lower stratosphere. Stratospheric composition is largely set by cross-tropopause transport in the tropics as tropospheric air predominantly enters the stratosphere in the tropics (Fueglistaler et al., 2009). Detailed numerical simulation of entire thunderstorm complexes is computationally expensive (Dauhut et al., 2015, 2018); the working hypothesis here is that it is useful to study the idealised fluid dynamics problem of penetration of a single artificially generated plume into a stably stratified layer.
The Stratospheric Quasi-Biennial Oscillation
The stratospheric quasi-biennial oscillation (QBO)
is an almost periodic, approximately axisymmetric
variation of the zonal (longitudinal) wind in the
equatorial mid-atmosphere. The oscillation is characterised by alternating, downward-propagating
easterly and westerly wind regimes and acts as the
dominant mode of interannual variability in the
stratosphere, the layer of the atmosphere lying
above the troposphere at roughly 15 to 50 km (100 - 1 hPa) in altitude. The wind regimes form in the
upper stratosphere and descend at approximately 1
km per month, dissipating in the lower stratosphere
an average of 28 months later, giving rise to a
quasi-biennial oscillation (Baldwin et al., 2001).
Application of atmospheric dynamical theory to the QBO started after its identification in the early 1960s, initially with the development of a mechanistic theory utilising wave/mean-flow interaction before later unravelling the intricate connection of the QBO with other atmospheric phenomena. This connection is both direct through the equatorial tropopause and indirect through the wider extratropical atmosphere; the fine details remain under consideration today. The difficulties of gathering observational data far above Earth's surface, particularly at sufficient spatial and temporal resolution, place the representation of the QBO and its teleconnections in global climate models under scrutiny to- day as satellite data improves and increased computational power allows the direct modelling of physical processes of greater complexity.
In this essay, we will discuss the dynamical behaviour of the QBO and its influence in the extratropical atmosphere, incorporating both mathematical and physical viewpoints in pursuit of understanding why such a phenomenon exists, how it fits into the broader picture of atmospheric dynamics, and where the influences may be felt. The remainder of section 1 provides a contextual discussion of the discovery and phenomenology of the QBO. In section 2, the basic dynamics are described with reference to a prototypical numerical model and wave/mean-flow theory. Finally, section 3 elucidates the extratropical effects of the QBO via a mechanistic approach to three illustrative examples of atmospheric variability modulated by the QBO.
Much of the discussion in this essay assumes familiarity with wave/mean-flow interaction, equatorial wave theory, and the (transformed) Eulerian-mean formalism. The pertinent details are made clear where necessary and full details can be found in the references herein.
Automated Spectrogram Analysis for Meteor Head Echoes
The Meteor Echo Spectrogram Analysis (MESA) program is developed to automatically identify meteor head echoes in spectrograms generated by forward-scatter radio meteor detection. The program is both extensible and flexible, allowing calculations such as line-of-sight approach and recede velocities, duration, and maximum intensity. A detection sensitivity of 0.790 is achieved, with an improved sensitivity of 0.875 when only low-noise spectrograms (~ 2/3 of the data) are analysed. The MESA program cannot fully replace manual analysis of spectrograms, but greatly reduces the volume of data that needs processing.
WGN, Volume 47, No. 2, April 2019, pp. 55 - 65
Journal received February 9, 2019
NASA ADS bibcode 2019JIMO...47...55P
International Meteor Conference 2018 report
The International Meteor Conference 2018 was held between 30th August and 2nd September in Pezinok, Slovakia, a city lying in the shadow of the Little Carpathian mountains.
Temporal and Spatial Variation of Meteor Flux in Radio Data
Charles Powell, Kristina Veljkovic
The variation of hourly detection counts from almost 350 radio meteor detection stations is analysed to determine the effect of year, time of day, and latitude on observations, as well as discussions of annual and monthly variations. Results indicate a significant increase in hourly detection counts in 2009-2010, supporting previous hypotheses of correlation between radio meteor detection rates and solar activity. Annual increases in meteor rates during summer months are noted, with no clear explanation. Monthly variations are not significant. The effect of latitude on detection counts is significant for years 2005-2016. For 12 of 17 considered years, night-time detection counts are greater than day-time counts, likely due to changes in ionospheric structure at night.
C. Powell, K. Veljkovic
WGN, Volume 45, No. 4, August 2017, pp. 73 - 81
Journal received September 6, 2017
NASA ADS bibcode 2017JIMO...45...73P
Modelling and Analysis of Diurnal Variation in Meteor Flux
Temporal and spatial variations of peak hour and idealised sine function fit are considered in reflection of an extended model of the diurnal shift mechanism. This model is formed by extension of the currently understood mechanism, providing a mathematical argument focusing on orbital velocity. Hourly detection counts collected by forward-scatter radio detection are used as data to analyse the form of diurnal shift for each observer. The fit and mean peak hour of the diurnal shift and are considered across nearly 350 observers, analysing variation from 2000 to 2016, as well as variation between data from 9 latitude and 14 longitude categories spanning at most 10 degrees each, to determine the agreement of data with the model. Modelling the orbital velocity of Earth as a primary factor behind diurnal variation is supported by the timezone corrected peak hours and correlation with longitude. The mechanism does not appear to vary with time, however the relative intensity of diurnal variation with respect to background detection counts is damped as a maximum in these hourly detection counts is observed. This provides a mathematical model of the diurnal shift mechanism, accompanied with support from a large dataset.
WGN, Volume 45, No. 2, April 2017, pp. 32 - 37
Journal received March 22, 2017
NASA ADS bibcode 2017JIMO...45...32P