A comparison of mean winds and gravity wave activity in the northern and southern polar MLT

Mean winds and waves observed in the mesosphere and lower thermosphere with MF radars located at Davis (69°S, 78°E) and Poker Flat (65°N, 147°W) are compared. Measurements covering the period from 1999 to mid 2000 show differences in the strength of the horizontal wind fields. In the southern hemisphere the zonal and meridional winds reach their maximum values near the summer solstice, but are delayed by 2–3 weeks in the northern hemisphere. Gravity wave variances also show significant differences, as do the strength of vertical velocities.Andrew Dowdy and Robert A. Vincent, Kiyoshi Igarashi and Yasuhiro Murayama, Damian J. Murph

Governing floods and riots: insurance, risk, and racism in the postwar United States

"In the late 1960s, the United States Federal Government resorted to publically funded insurance systems to deal with two quite different problems: floods and riots. Both programs were administered by the same agency, both relied heavily on the spatial mapping of risk, and both were haunted by problems of moral hazard. Curiously, and most importantly, however, riots as well as floods were viewed as 'environmental hazards' by the insurance industry and the government agencies involved. The underlying assumption was that social problems could be treated as quasi-natural hazards, i.e. as a homogeneous and unpredictable force that could be contained by actuarial means. Yet uprisings, civil commotions, and riots are not 'acts of god' that are located outside of society (and neither are floods). This article discloses the origins of both programs, it describes their communalities and differences, and it reveals the views of those who were subject to racist steering practices." (author's abstract)"In den späten 1960er Jahren begegnete die US-amerikanische Bundesregierung zwei recht unterschiedlichen Problemen - Überschwemmungen und Riots - durch die Schaffung von öffentlich finanzierten Versicherungssystemen. Beide Programme wurden von derselben Behörde verwaltet, beide Programme waren gekennzeichnet durch die Kartierung von Risiken, und beide Programme litten unter dem Problem des 'moral hazard'. Die interessanteste Gemeinsamkeit bestand jedoch darin, dass sowohl Überschwemmungen wie auch riots von den Versicherungsgesellschaften und staatlichen Institutionen als 'Umweltrisiken' behandelt wurden. Die implizite Annahme war dabei, dass soziale Probleme als quasi-natürliche Gefahren, d.h. als eine homogene und unberechenbare Gewalt betrachtet werden konnten, die man aber durch die Anwendung von Versicherungstechniken wieder in den Griff bekam. Aufstände, Unruhen, Revolten, etc., sind jedoch nicht das Ergebnis 'höherer Gewalt' (ebenso wenig wie Überschwemmungen) und damit auch nicht außerhalb der Gesellschaft zu verorten. Dieser Artikel erklärt die historischen Ursprünge beider Programme, er beschreibt deren Gemeinsamkeiten und Unterschiede, und er gibt die Sichtweisen derjenigen wieder, die sich rassistischen Regulierungspraktiken ausgesetzt sahen." (Autorenreferat

Physics in the mesosphere/lower thermosphere: A personal perspective

The scope of this paper is to present some progress being made in the last few decades regarding some aspects of physical processes in the mesosphere/lower thermosphere and to point to some open questions. This summary is presented from a personal perspective, i.e., this is not a review of a certain science topic. Most citations reflect my own work or are representative examples only. They are not meant to be complete or comprehensive

Polar mesosphere summer echoes (PMSE): review of observations and current understanding

International audiencePolar mesosphere summer echoes (PMSE) are very strong radar echoes primarily studied in the VHF wavelength range from altitudes close to the polar summer mesopause. Radar waves are scattered at irregularities in the radar refractive index which at mesopause altitudes is solely determined by the electron number density. For efficient scatter, the electron number density must reveal structures at the radar half wavelength (Bragg condition; ~3 m for typical VHF radars). The question how such small scale electron number density structures are created in the mesopause region has been a longstanding open scientific question for almost 30 years. This paper reviews experimental and theoretical milestones on the way to an advanced understanding of PMSE. Based on new experimental results from in situ observations with sounding rockets, ground based observations with radars and lidars, numerical simulations with microphysical models of the life cycle of mesospheric aerosol particles, and theoretical considerations regarding the diffusivity of electrons in the ice loaded complex plasma of the mesopause region, a consistent explanation for the generation of these radar echoes has been developed. The main idea is that mesospheric neutral air turbulence in combination with a significantly reduced electron diffusivity due to the presence of heavy charged ice aerosol particles (radii ~5?50 nm) leads to the creation of structures at spatial scales significantly smaller than the inner scale of the turbulent velocity field itself. Importantly, owing to their very low diffusivity, the plasma structures acquire a very long lifetime, i.e. 10 min to hours in the presence of particles with radii between 10 and 50 nm. This leads to a temporal decoupling of active neutral air turbulence and the existence of small scale plasma structures and PMSE and thus readily explains observations proving the absence of neutral air turbulence at PMSE altitudes. With this explanation at hand, it becomes clear that PMSE are a suitable tool to permanently monitor the thermal and dynamical structure of the mesopause region allowing insights into important atmospheric key parameters like temperatures, winds, gravity wave parameters, turbulence, solar cycle effects, and long term changes

Photochemical 1,3-Acyl Shifts in Natural Product Synthesis

Photochemical, sigmatropic 1,3-acyl shifts represent a powerful tool to construct quaternary carbon atoms and the backbones of complex natural products which cannot be constructed easily by conventional methods. This review highlights applications of 1,3-acyl shifts to elegant, partly biomimetic total syntheses of natural products by discussing the underlying photochemical equilibrium

VAHCOLI, a new concept for lidars: technical setup, science applications, and first measurements

A new concept for a cluster of compact lidar systems named VAHCOLI (Vertical And Horizontal COverage by LIdars) is presented, which allows for the measurement of temperatures, winds, and aerosols in the middle atmosphere (10 110 km) with high temporal and vertical resolution of minutes and some tens of meters, respectively, simultaneously covering horizontal scales from a few hundred meters to several hundred kilometers ( four-dimensional coverage ). The individual lidars ( units ) being used in VAHCOLI are based on a diode-pumped alexandrite laser, which is currently designed to detect potassium (D 770 nm), and on sophisticated laser spectroscopy measuring all relevant frequencies (seeder laser, power laser, backscattered light) with high temporal resolution (2 ms) and high spectral resolution applying Doppler-free spectroscopy. The frequency of the lasers and the narrowband filter in the receiving system are stabilized to typically 10 100 kHz, which is a factor of roughly 105 smaller than the Doppler-broadened Rayleigh signal. Narrowband filtering allows for the measurement of Rayleigh and/or resonance scattering separately from the aerosol (Mie) signal during both night and day. Lidars used for VAHCOLI are compact (volume: 1m3) and multi-purpose systems which employ contemporary electronic, optical, and mechanical components. The units are designed to autonomously operate under harsh field conditions in remote locations. An error analysis with parameters of the anticipated system demonstrates that temperatures and line-of-sight winds can be measured from the lower stratosphere to the upper mesosphere with an accuracy of (0.1 5)K and (0.1 10)ms1, respectively, increasing with altitude. We demonstrate that some crucial dynamical processes in the middle atmosphere, such as gravity waves and stratified turbulence, can be covered by VAHCOLI with sufficient temporal, vertical, and horizontal sampling and resolution. The four-dimensional capabilities of VAHCOLI allow for the performance of time-dependent analysis of the flow field, for example by employing Helmholtz decomposition, and for carrying out statistical tests regarding, for example, intermittency and helicity. The first test measurements under field conditions with a prototype lidar were performed in January 2020. The lidar operated successfully during a 6-week period (night and day) without any adjustment. The observations covered a height range of 5 100 km and demonstrated the capability and applicability of this unit for the VAHCOLI concept

Thank you for Smoking! The Discursive Battle about the Meaning of Smoking

Thesis purpose: The purpose of the master thesis is to analyse the battle of meaning creation regarding the notion of smoking and to reveal the production of unequal power relations. The battle is fought by different stakeholders through means of language and the study focuses on the tobacco industry in Germany. Methodology: A critical discourse analysis is applied with a qualitative research strategy. Our data collection was inspired by grounded theory and is limited in scope through a relevant case within the context of smoking in Germany. Empirical data is collected by means of an internet based document study of publicly available texts. Metaphors are used to structure our analysis of selected texts. Theoretical perspective: Critical discourse analysis and related theories as discourse analysis and the construction of reality by means of language form the theoretical frame. Empirical data: Different types of documents, such as corporate websites, magazines, scientific articles, reports and forum texts of the identified stakeholder groups are included in the analysis. Conclusion: The identified stakeholders assign different meanings to the notion of smoking through language use. The analysis reveals with what meaning the notion is filled and what they accomplish by establishing their meaning of smoking as normal. Contradictory goals can be found within the same stakeholder group. The thesis contributes to existing research on the German tobacco market and the use of language in that context

Absolute density measurements in the middle atmosphere

In the last ten years a total of 25 sounding rockets employing ionization gauges have been launched at high latitudes ( ~ 70° N) to measure total atmospheric density and its small scale fluctuations in an altitude range between 70 and 110 km. While the determination of small scale fluctuations is unambiguous, the total density analysis has been complicated in the past by aerodynamical disturbances leading to densities inside the sensor which are enhanced compared to atmospheric values. Here, we present the results of both Monte Carlo simulations and wind tunnel measurements to quantify this aerodynamical effect. The comparison of the resulting ‘ram-factor’ profiles with empirically determined density ratios of ionization gauge measurements and falling sphere measurements provides excellent agreement. This demonstrates both the need, but also the possibility, to correct aerodynamical influences on measurements from sounding rockets. We have determined a total of 20 density profiles of the mesosphere-lower-thermosphere (MLT) region. Grouping these profiles according to season, a listing of mean density profiles is included in the paper. A comparison with density profiles taken from the reference atmospheres CIRA86 and MSIS90 results in differences of up to 40%. This reflects that current reference atmospheres are a significant potential error source for the determination of mixing ratios of, for example, trace gas constituents in the MLT region

Seasonal changes in gravity wave activity measured by lidars at mid-latitudes

More than 230 nights of temperature measurements between 1 and 105 km have been performed at the Leibniz-Institute of Atmospheric Physics in Kühlungsborn with a combination of two different lidars, i.e. a Rayleigh-Mie-Raman lidar and a potassium lidar. About 1700 h of measurements have been collected between 2002 and 2006. Apart from some gaps due to the adverse weather conditions the measurements are well distributed throughout the year. Comprehensive information about the activity of medium- and low-frequency gravity waves was extracted from this data set. The dominating vertical wavelengths found are between 10 and 20 km and do not show any seasonal variation. In contrast the temperature fluctuations due to gravity waves experience a clear annual cycle with a maximum in winter. The most significant differences exist around 60 km where the fluctuations in winter are more than two times larger than they are in summer. Only small seasonal differences are observed above 90 km and below 35 km. Generally, the fluctuations grow from about 0.5 K up to 8 K between 20 and 100 km. Damping of waves is observed at nearly all altitudes and in all seasons. The planetary wave activity shows a similar structure in altitude and season as the gravity wave activity which indicates that similar mechanisms influencing different scales. Combining the monthly mean temperatures and the fluctuations we show that the transition between winter and summer season and vice versa seems to start in the mesopause region and to penetrate downward