Nonlinear stratospheric variability: multifractal detrended fluctuation analysis and singularity spectra

Characterising the stratosphere as a turbulent system, temporal fluctuations often show different correlations for different time scales as well as intermittent behaviour that cannot be captured by a single scaling exponent. In this study, the different scaling laws in the long term stratospheric variability are studied using Multifractal de-trended Fluctuation Analysis. The analysis is performed comparing four re-analysis products and different realisations of an idealised numerical model, isolating the role of topographic forcing and seasonal variability, as well as the absence of climate teleconnections and small-scale forcing. The Northern Hemisphere (NH) shows a transition of scaling exponents for time scales shorter than about one year, for which the variability is multifractal and scales in time with a power law corresponding to a red spectrum, to longer time scales, for which the variability is monofractal and scales in time with a power law corresponding to white noise. Southern Hemisphere (SH) variability also shows a transition at annual scales. The SH also shows a narrower dynamical range in multifractality than the NH, as seen in the generalised Hurst exponent and in the singularity spectra. The numerical integrations show that the models are able to reproduce the low-frequency variability but are not able to fully capture the shorter term variability of the stratosphere

The efficacy of the genus epidemicus remedy in the treatment of influenza

M.Tech. (Homoeopathy)Influenza is a highly infectious illness caused by the influenza A or B viruses. Together with the high infectivity rates, relatively short incubation period and the genetic lability of the influenza virus, influenza can cause overwhelming epidemics and thus become extremely problematic to world public health (Bannister et al., 1996: 131-134). Influenza and influenza-like syndromes are responsible for one third of absenteeism in the workplace and it is due to this that prophylactic and curative measures have become necessary (papp et al., 1998: 69-76). In homoeopathyit is known that treatment of an epidemic with the genus epidemicus remedy should be effective in the majority of cases (Kent, 1979: 33-39). This remedy is carefully chosen on account of its similarity to the main presenting symptoms displayed in all cases of the respective year's influenza picture. The aim of this study . was to demonstrate the effectiveness of the genus epidemicus remedy indicated for the current year's influenza epidemic, namely Arsenicum album. It was administered in a 30CH potency. The efficacy of the genus epidemicus remedy in the treatment of influenza was assessed by investigating the intensity and duration of influenza symptoms over a specified period of time, this being four days, in a suitable sample group. The sample group was selected and obtained in a clinical setting. The sample group was randomly divided into an experimental group and a control group of fifteen participants respectively. Symptoms were monitored with the use of a questionnaire (Appendix C). Placebos were administered to the control group and Arsenicum album 30CH was administered to the experimental group. The medication was administered as a single dose of five pillules three times daily. The first dose of medication was administered in the clinician's office on commencement of the study and the following. six doses were to be taken three times daily, in the morning, at lunch and in the evening, by the participants themselves. Data was analysed by means of the Mann-Whitney statistical test. The experimental and control groups were analysed separately. Group A was determined to be the control group and Group B was determined to be the experimental group. Effectiveness ofArsenicum album 30CH in the treatment of influenza was defined as a statistically significant greater decrease in the symptom severity over time in the experimental group, Group B, as compared with the control group, Group A. From statistical evaluation it was determined that the homoeopathic remedy, Arsenicum album 30CH, was the indicated genus epidemicus remedy for the influenza epidemic of the winter of 2001. It was further determined that Arsenicum album 30CH was effective in reducing the severity of symptoms of influenza or influenza-like syndrome and was thus effective in the treatment of influenza and influenza-like syndrome

A Search for Chaotic Behavior in Northern Hemisphere Stratospheric Variability

Northern Hemisphere stratospheric variability is investigated with respect to chaotic behavior using time series from three different variables extracted from four different reanalysis products and two numerical model runs with different forcing. The time series show red spectra at all frequencies and the probability distribution functions show persistent deviations from a Gaussian distribution. An exception is given by the numerical model forced with perpetual winter conditions—a case that shows more variability and follows a Gaussian distribution, suggesting that the deviation from Gaussianity found in the observations is due to the transition between summer and winter variability. To search for the presence of a chaotic attractor the correlation dimension and entropy, the Lyapunov spectrum, and the associated Kaplan–Yorke dimension are estimated. A finite value of the dimensions can be computed for each variable and data product, with the correlation dimension ranging between 3.0 and 4.0 and the Kaplan–Yorke dimension between 3.3 and 5.5. The correlation entropy varies between 0.6 and 1.1. The model runs show similar values for the correlation and Lyapunov dimensions for both the seasonally forced run and the perpetual-winter run, suggesting that the structure of a possible chaotic attractor is not determined by the seasonality in the forcing, but must be given by other mechanisms

Assimilation of atmospheric infrasound data to constrain tropospheric and stratospheric winds

This data assimilation study exploits infrasound from explosions to probe an atmospheric wind component from the ground up to stratospheric altitudes. Planned explosions of old ammunition in Finland generate transient infrasound waves that travel through the atmosphere. These waves are partially reflected back towards the ground from stratospheric levels, and are detected at a receiver station located in northern Norway at 178 km almost due North from the explosion site. The difference between the true horizontal direction towards the source and the backazimuth direction(the horizontal direction of arrival) of the incoming infrasound wave-fronts, in combination with the pulse propagation time, are exploited to provide an estimate of the average cross-wind component in the penetrated atmosphere. We perform offline assimilation experiments with an ensemble Kalman filter and these observations, using the ERA5 ensemble reanalysis atmospheric product as background(prior) for the wind at different vertical levels. We demonstrate that information from both source scan be combined to obtain analysis (posterior) estimates of cross-winds at different vertical levels of the atmospheric slice between the explosion site and the recording station. The assimilation makes greatest impact at the 12−60 km levels, with some changes with respect to the prior of the order of 0.1−1.0 m/s, which is a magnitude larger than the typical standard deviation of the ERA5 background. The reduction of background variance in the higher levels often reached 2−5%. This is the first published study demonstrating techniques to implement assimilation of infrasound data into atmospheric models. It paves the way for further exploration in the use of infrasound observations– especially natural and continuous sources – to probe the middle atmospheric dynamics and to assimilate these data into atmospheric model products

The role of synoptic eddies in the tropospheric response to stratospheric variability

The tropospheric response to sudden stratospheric warmings (SSWs) is analyzed in an idealized model setup regarding the respective roles of planetary-scale and synoptic-scale waves. The control model run includes a full interactive wave spectrum, while a second run includes interactive planetary-scale waves but only the time-mean synoptic-scale wave forcing from the control run. In both runs, the tropospheric response is characterized by the negative phase of the respective tropospheric annular mode. But given their different latitudinal structure, the control run shows the expected response, i.e., an equatorward shift of the tropospheric jet, whereas the response in the absence of interactive synoptic eddies is characterized by a poleward jet shift. This opposite jet shift is associated with a different planetary wave variability that couples with the zonal flow between the stratosphere and the surface. These results indicate that the synoptic eddy feedback is necessary for the observed tropospheric response to SSWs

Stratosphere - troposphere coupling by planetary waves

The stratosphere and troposphere exhibit strong coupling during the active seasons of the stratosphere (winter/spring in the Northern/Southern Hemispheres), which are characterized by bursts of planetary-scale Rossby waves and by large stratospheric wind and temperature anomalies (major or minor warmings), which may be accompanied by tropospheric flow anomalies. We here explore further the role of planetary wave bursts in creating these anomalies and in stratosphere – troposphere coupling. This kind of variability is now well known to occur spontaneously in models of a wide range of complexity. This paper seeks to contribute to the understanding of such variability within a quasi-linear framework. This is done by employing a linear model to diagnose Rossby wave behavior in a general circulation model of intermediate complexity (a spectral core model) in cases in which the model exhibits such variability. Resonance theory is suggested to provide a means to understand stratosphere – troposphere coupling immediately prior to the onset of wave bursts and the accompanying stratospheric warmings and tropospheric anomalies

Increased vertical resolution in the stratosphere reveals role of gravity waves after sudden stratospheric warmings

Sudden stratospheric warmings (SSWs) have a long-lasting effect within the stratosphere as well as impacts on the underlying troposphere. However, sub-seasonal forecasts of the winter polar stratosphere fail to use their full potential for predictability as they tend to underestimate the magnitude and persistence of these events already within the stratosphere. The origin of this underestimation is unknown. Here, we demonstrate that the associated polar stratospheric cold bias following SSW events in sub-seasonal hindcasts can be halved by increasing vertical model resolution, suggesting a potential sensitivity to gravity wave forcing. While the predictability of the planetary Rossby wave flux into the stratosphere at lead times longer than a week is limited, the existence of a critical layer for gravity waves with a low zonal phase speed caused by the disturbed polar vortex provides predictability to the upper stratosphere. Gravity wave breaking near that critical layer can, therefore, decelerate the zonal flow consistently with anomalous subsidence over the polar cap leading to warmer temperatures in the middle polar stratosphere. Since the spectrum of gravity waves involves vertical wavelengths of less than 4000 m, as estimated by wavelet analysis, a high vertical model resolution is needed to resolve the positive feedback between gravity wave forcing and the state of the polar vortex. Specifically, we find that at a spectral resolution of TCo639 (approximate horizontal grid spacing of 18 km) at least 198 levels are needed to correctly resolve the spectrum of gravity waves in the ECMWF Integrated Forecasting System. Increasing vertical resolution in operational forecasts will help to mitigate stratospheric temperature biases and improve sub-seasonal predictions of the stratospheric polar vortex