A record of the geomagnetic field on the ground sometimes shows smooth daily variations on the order of a few tens of nano teslas. These daily variations, commonly known as Sq, are caused by electric ...currents of several
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flowing on the sunlit side of the E-region ionosphere at about 90–150 km heights. We review advances in our understanding of the geomagnetic daily variation and its source ionospheric currents during the past 75 years. Observations and existing theories are first outlined as background knowledge for the non-specialist. Data analysis methods, such as spherical harmonic analysis, are then described in detail. Various aspects of the geomagnetic daily variation are discussed and interpreted using these results. Finally, remaining issues are highlighted to provide possible directions for future work.
The geomagnetic Kp index is one of the most extensively used indices of geomagnetic activity, both for scientific and operational purposes. This article reviews the properties of the Kp index and ...provides a reference for users of the Kp index and associated data products as derived and distributed by the GFZ German Research Centre for Geosciences. The near real‐time production of the nowcast Kp index is of particular interest for space weather services and here we describe and evaluate its current setup.
Key Points
Production and distribution of nowcast and definitive Kp index and derived products
Kp is estimated to have decreased from 1932 to 2020 by one third of a unit due to geomagnetic secular variation
Improved agreement between nowcast and definitive Kp since August 2020
A sudden stratospheric waring occurred in the southern hemisphere during September 2019, accompanied by an exceptionally strong quasi‐6‐day wave (Q6DW). We examine the ionospheric response using ...global total electron content (TEC) maps, with a focus on the short‐period variability (5–48 h). A Fourier analysis of the TEC data reveals ionospheric variations associated with the secondary waves due to the non‐linear interaction between the Q6DW and atmospheric tides. The largest signatures among them are related to the ∼29‐h standing oscillation, which is attributable to the Q6DW interaction with the migrating diurnal tide, with the maximum amplitude ∼8% of the zonal mean. Also detected are the signatures associated with the westward‐propagating ∼13‐h oscillation with the zonal wavenumber 1 (∼4%) and westward‐propagating ∼11‐h oscillation with the zonal wavenumber 3 (∼3%), both of which can be attributed to the Q6DW interaction with the migrating semidiurnal tide. The signatures related to the Q6DW interaction with the migrating terdiurnal tide and some non‐migrating tides are also observed. This is the first time that secondary wave signatures of the Q6DW‐tidal interaction are identified in ionospheric observations with predicted zonal wavenumbers and periods. The oscillations are symmetric about the magnetic equator with amplitude peaks at ±20° magnetic latitudes, suggesting that the oscillations are generated by the modulation of the equatorial plasma fountain.
Key Points
Spectrum analysis is performed on total electron content during the quasi‐6‐day wave event in September 2019
Signatures of secondary waves from the non‐linear interaction of the quasi‐6‐day wave with tides are detected
The wave signatures result from the modulation of the equatorial plasma fountain
An exceptionally strong stationary planetary wave with Zonal Wavenumber 1 led to a sudden stratospheric warming (SSW) in the Southern Hemisphere in September 2019. Ionospheric data from European ...Space Agency's Swarm satellite constellation mission show prominent 6‐day variations in the dayside low‐latitude region at this time, which can be attributed to forcing from the middle atmosphere by the Rossby normal mode “quasi‐6‐day wave” (Q6DW). Geopotential height measurements by the Microwave Limb Sounder aboard National Aeronautics and Space Administration's Aura satellite reveal a burst of global Q6DW activity in the mesosphere and lower thermosphere during the SSW, which is one of the strongest in the record. The Q6DW is apparently generated in the polar stratosphere at 30–40 km, where the atmosphere is unstable due to strong vertical wind shear connected with planetary wave breaking. These results suggest that an Antarctic SSW can lead to ionospheric variability through wave forcing from the middle atmosphere.
Plain Language Summary
A sudden stratospheric warming (SSW) is an extreme wintertime polar meteorological phenomenon occurring mostly over the Arctic region. Studies have shown that Arctic SSW can influence the entire atmosphere. In September 2019, a rare SSW event occurred in the Antarctic region, providing an opportunity to investigate its broader impact on the whole atmosphere. We present observations from the middle atmosphere and ionosphere during this event, noting unusually strong wave activity throughout this region. Our results suggest that an Antarctic SSW can have a significant impact on the whole atmosphere system similar to those due to Arctic events.
Key Points
An Antarctic sudden stratospheric warming (SSW) occurred in September 2019
Swarm observations reveal prominent 6‐day variations in the dayside low‐latitude ionosphere
A burst of quasi‐6‐day wave activity is observed in the middle atmosphere during the SSW
Belt-like tight junctions (TJs), referred to as zonula occludens, have long been regarded as a specialized differentiation of epithelial cell membranes. They are required for cell adhesion and ...paracellular barrier functions, and are now thought to be partly involved in fence functions and in cell polarization. Recently, the molecular bases of TJs have gradually been unveiled. TJs are constructed by TJ strands, whose basic frameworks are composed of integral membrane proteins with four transmembrane domains, designated claudins. The claudin family is supposedly composed of at least 24 members in mice and humans. Other types of integral membrane proteins with four transmembrane domains, namely occludin and tricellulin, as well as the single transmembrane proteins, JAMs (junctional adhesion molecules) and CAR (coxsackie and adenovirus receptor), are associated with TJ strands, and the high-level organization of TJ strands is likely to be established by membrane-anchored scaffolding proteins, such as ZO-1/2. Recent functional analyses of claudins in cell cultures and in mice have suggested that claudin-based TJs may have pivotal functions in the regulation of the epithelial microenvironment, which is critical for various biological functions such as control of cell proliferation. These represent the dawn of 'Barriology' (defined by Shoichiro Tsukita as the science of barriers in multicellular organisms). Taken together with recent reports regarding changes in claudin expression levels, understanding the regulation of the TJ-based microenvironment system will provide new insights into the regulation of polarization in the respect of epithelial microenvironment system and new viewpoints for developing anticancer strategies.
Invariance under the charge, parity, time-reversal (CPT) transformation is one of the fundamental symmetries of the standard model of particle physics. This CPT invariance implies that the ...fundamental properties of antiparticles and their matter-conjugates are identical, apart from signs. There is a deep link between CPT invariance and Lorentz symmetry--that is, the laws of nature seem to be invariant under the symmetry transformation of spacetime--although it is model dependent. A number of high-precision CPT and Lorentz invariance tests--using a co-magnetometer, a torsion pendulum and a maser, among others--have been performed, but only a few direct high-precision CPT tests that compare the fundamental properties of matter and antimatter are available. Here we report high-precision cyclotron frequency comparisons of a single antiproton and a negatively charged hydrogen ion (H(-)) carried out in a Penning trap system. From 13,000 frequency measurements we compare the charge-to-mass ratio for the antiproton (q/m)p- to that for the proton (q/m)p and obtain (q/m)p-/(q/m)p − 1 =1(69) × 10(-12). The measurements were performed at cyclotron frequencies of 29.6 megahertz, so our result shows that the CPT theorem holds at the atto-electronvolt scale. Our precision of 69 parts per trillion exceeds the energy resolution of previous antiproton-to-proton mass comparisons as well as the respective figure of merit of the standard model extension by a factor of four. In addition, we give a limit on sidereal variations in the measured ratio of <720 parts per trillion. By following the arguments of ref. 11, our result can be interpreted as a stringent test of the weak equivalence principle of general relativity using baryonic antimatter, and it sets a new limit on the gravitational anomaly parameter of |α − 1| < 8.7 × 10(-7).
A quantitative comparison of the geomagnetic lunar tide and lower stratospheric parameters (zonal mean air temperature T and zonal mean zonal wind U) is carried out for the period 1958–2007. The ...correlation between the amplitude of the geomagnetic lunar tide at an equatorial station, Addis Ababa, and the lower stratospheric parameters from the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP‐NCAR) reanalysis is examined. It is found that the lunar tidal amplitude tends to be positively and negatively correlated with the stratospheric T and U, respectively, in high latitudes of the Northern Hemisphere during December and January. High correlations are observed in approximately 70% of stratospheric sudden warming (SSW) events. The results suggest that variability of the geomagnetic lunar tide during the northern winter is closely linked with dynamical changes in the lower stratospheric parameters associated with SSWs.
Key Points
Comparison between stratospheric parameters and the geomagnetic lunar tide
Analysis of long‐term data for 1958‐2007
Significant changes in the geomagnetic lunar tide during SSWs
This paper examines the response of the upper atmosphere to equatorial Kelvin waves with a period of ∼3 days, also known as ultrafast Kelvin waves (UFKWs). The whole atmosphere model ...Ground‐to‐topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) is used to simulate the UFKW events in the late summer of 2010 and 2011 as well as in the boreal winter of 2012/2013. When the lower layers of the model below 30‐km altitude are constrained with meteorological data, GAIA is able to reproduce salient features of the UFKW in the mesosphere and lower thermosphere as observed by the Aura Microwave Limb Sounder. The model also reproduces ionospheric response, as validated through comparisons with total electron content data from the Gravity field and steady‐state Ocean Circulation Explorer satellite as well as with earlier observations. Model results suggest that the UFKW produces eastward‐propagating ∼3‐day variations with zonal wavenumber 1 in the equatorial zonal electric field and F region plasma density. Model results also suggest that for a ground observer, identifying ionospheric signatures of the UFKW is a challenge because of ∼3‐day variations due to other sources. This issue can be overcome by combining ground‐based measurements from different longitudes. As a demonstration, we analyze ground‐based magnetometer data from equatorial stations during the 2011 event. It is shown that wavelet spectra of the magnetic data at different longitudes are only in partial agreement, with or without a ∼3‐day peak, but a spectrum analysis based on multipoint observations reveals the presence of the UFKW.
Key Points
GAIA simulations are performed for ultrafast Kelvin wave (UFKW) in the middle and upper atmosphere
UFKW produces eastward‐propagating ∼3‐day ionospheric variations with zonal wavenumber 1
First magnetic detection of UFKW in the equatorial electrojet is also presented
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