North-South asymmetries in the polar thermosphere-ionosphere system: solar cycle and seasonal influences

Previous studies have revealed that ion drift and neutral wind speeds at ~400 km in the polar cap (>80° magnetic latitude) are on average larger in the Northern Hemisphere (NH) than in the Southern Hemisphere, which is at least partly due to asymmetry in the geomagnetic field. Here we investigate for the first time how these asymmetries depend on season and on solar/geomagnetic activity levels. Ion drift measurements from the Cluster mission show little seasonal dependence in their north-south asymmetry when all data (February 2001–December 2013) are used, but the asymmetry disappears around June solstice for high solar activity and around December solstice for low solar activity. Neutral wind speeds in the polar cap obtained from the Challenging Minisatellite Payload spacecraft (January 2002–December 2008) are always larger in the summer hemisphere, regardless of solar activity, but the high-latitude neutral wind vortices at dawn and dusk tend to be stronger in the NH, except around December solstice, in particular, when solar activity is low. Simulations with the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) more or less capture the behavior of the ion drift speeds, which can be explained as a superposition of seasonal and geomagnetic field effects, with the former being stronger for higher solar activity. The behavior of the neutral wind speed and vorticity is not accurately captured by the model. This is probably due to an incorrect seasonal cycle in plasma density around ~400 km in CMIT, which affects the ion drag force. This must be addressed in future work

The role of the Sun in long-term change in the F2 peak ionosphere: new insights from EEMD and numerical modelling

We applied Ensemble Empirical Mode Decomposition (EEMD) for the first time to ionosonde data to study trends in the critical frequency of the F2 peak, foF2, and its height, hmF2, from 1959 to 2005. EEMD decomposes a time series into several quasi-cyclical components, called Intrinsic Mode Functions (IMFs), and a residual, which can be interpreted as a long-term trend. In contrast to the more commonly used linear regression-based trend analysis, EEMD makes no assumptions on the functional form of the trend and no separate correction for the influence of solar activity variations is needed. We also adopted a more rigorous significance testing procedure with less restrictive underlying assumptions than the F-test, which is normally used as part of a linear regression-based trend analysis. EEMD analysis shows that trends in hmF2 and foF2 between 1959 and 2005 are mostly highly linear, but the F-test tends to overestimate the significance of trends in hmF2 and foF2 in 30% and 25% of cases, respectively. EEMD-based trends are consistently more negative than linear regression-based trends, by 30-35% for hmF2 and about 50% for foF2. This may be due to the different treatment of the influence of a long-term decrease in solar activity from 1959 to 2005. We estimate the effect of this decrease in solar activity with two different data-based methods as well as using numerical model simulations. While these estimates vary, all three methods demonstrate a larger relative influence of the Sun on trends in foF2 than on trends in hmF2

The impact of century-scale changes in the core magnetic field on external magnetic field contributions

The Earth’s internal magnetic field controls to a degree the strength, geographic positioning, and structure of currents flowing in the ionosphere and magnetosphere, which produce their own (external) magnetic fields. The secular variation of the Earth’s internal magnetic field can therefore lead to long-term changes in the externally produced magnetic field as well. Here we will examine this more closely. First, we obtain scaling relations to describe how the strength of magnetic perturbations associated with various different current systems in the ionosphere and magnetosphere depends on the internal magnetic field intensity. Second, we discuss how changes in the orientation of a simple dipolar magnetic field will affect the current systems. Third, we use model simulations to study how actual changes in the Earth’s internal magnetic field between 1908 and 2008 have affected some of the relevant current systems. The influence of the internal magnetic field on low- to mid-latitude currents in the ionosphere is relatively well understood, while the effects on high-latitude current systems and currents in the magnetosphere still pose considerable challenges

Introduction to special issue on "Long-term changes and trends in the stratosphere, mesosphere, thermosphere and ionosphere"

This special issue bundles some of the latest results on decadal-scale variations in the stratosphere, mesosphere, thermosphere, and ionosphere, following on from the 8th Workshop on Long-Term Changes and Trends in the Atmosphere, held in Cambridge, UK, on 28–31 July 2014. Emmert et al. (2015) provided a short report of the workshop. This introduction briefly describes the relevance of the field and highlights some of the recent progress that has been mad

Long-term geospace climate monitoring

Climate change is characterized by global surface warming associated with the increase of greenhouse gas population since the start of the industrial era. Growing evidence shows that the upper atmosphere is experiencing appreciable cooling over the last several decades. The seminal modeling study by Roble and Dickinson (1989) suggested potential effects of increased greenhouse gases on the ionosphere and thermosphere cooling which appear consistent with some observations. However, several outstanding issues remain regarding the role of CO2, other important contributors, and impacts of the cooling trend in the ionosphere and thermosphere: for example, (1) what is the regional variability of the trends? (2) the very strong ionospheric cooling observed by multiple incoherent scatter radars that does not fit with the prevailing theory based on the argument of anthropogenic greenhouse gas increases, why? (3) what is the effect of secular changes in Earth’s main magnetic field? Is it visible now in the ionospheric data and can it explain some of the regional variability in the observed ionospheric trends? (4) what is the impact of long-term cooling in the thermosphere on operational systems? (5) what are the appropriate strategic plans to ensure the long-term monitoring of the critical space climate

Effectiveness of a guided self-help exercise program tailored to patients treated with total laryngectomy:Results of a multi-center randomized controlled trial

Objective: To investigate the effectiveness of a guided self-help exercise program on swallowing, speech, and shoulder problems in patients treated with total laryngectomy (TL). Materials and methods: This randomized controlled trial included patients treated with TL in the last 5 years. Patients were randomized into the intervention group (self-help exercise program with flexibility, range-of-motion and lymphedema exercises and self-care education program) or control group (self-care education program). Both groups completed measurements before and 3 and 6-months after randomization. The primary outcome was swallowing problems (SWAL-QOL). Secondary outcomes were speech problems (SHI), shoulder problems (SDQ), self-management (patient activation: PAM) and health-related quality of life (HRQOL: EORTC QLQ-C30/H&N35). Adherence was defined as moderate-high in case a patient exercised >1 per day. Linear mixed model analyses were conducted to investigate the effectiveness of the intervention and to investigate whether neck dissection, treatment indication (primary/salvage TL), time since treatment, severity of problems, and preferred format (online/booklet) moderated the effectiveness. Results: Moderate-high adherence to the exercise program was 59%. The intervention group (n = 46) reported less swallowing and communication problems over time compared to the control group (n = 46) (p-value = 0.013 and 0.004). No difference was found on speech, shoulder problems, patient activation and HRQOL. Time since treatment moderated the effectiveness on speech problems (p-value = 0.025): patients within 6 months after surgery benefitted most from the intervention. Being treated with a neck dissection, treatment indication, severity of problems and format did not moderate the effectiveness. Conclusion: The guided self-help exercise program improves swallowing and communication. Trial registration. NTR5255

The importance of geomagnetic field changes versus rising CO2 levels for long-term change in the upper atmosphere

The Earth’s upper atmosphere has shown signs of cooling and contraction over the past decades. This is generally attributed to the increasing level of atmospheric CO2, a coolant in the upper atmosphere. However, especially the charged part of the upper atmosphere, the ionosphere, also responds to the Earth’s magnetic field, which has been weakening considerably over the past century, as well as changing in structure. The relative importance of the changing geomagnetic field compared to enhanced CO2 levels for long-term change in the upper atmosphere is still a matter of debate. Here we present a quantitative comparison of the effects of the increase in CO2 concentration and changes in the magnetic field from 1908 to 2008, based on simulations with the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM). This demonstrates that magnetic field changes contribute at least as much as the increase in CO2 concentration to changes in the height of the maximum electron density in the ionosphere, and much more to changes in the maximum electron density itself and to low-/mid-latitude ionospheric currents. Changes in the magnetic field even contribute to cooling of the thermosphere at ~300 km altitude, although the increase in CO2 concentration is still the dominant factor here. Both processes are roughly equally important for long-term changes in ion temperature