Objectives
The objective of this study was to investigate the influence of the COVID-19 pandemic on physical activity (PA) and the incidence of frailty among initially non-frail older adults in ...Japan.
Design
A follow-up online survey.
Setting and Subjects
Among the 1,600 baseline online survey participants, 388 adults were already frail, and 275 older adults did not respond to the follow-up survey. Thus, the final number of participants in this study was 937 (follow-up rate: 77.3%).
Methods
We assessed the total PA time at four time points according to the COVID-19 waves in Japan: January 2020 (before the pandemic), April 2020 (during the first wave), August 2020 (during the second wave), and January 2021 (during the third wave). We then investigated the incidence of frailty during a one-year follow-up period (during the pandemic).
Results
The total PA time during the first, second, and third waves of the pandemic decreased from the pre-pandemic PA time by 33.3%, 28.3%, and 40.0%, respectively. In particular, the total PA time of older adults who were living alone and socially inactive decreased significantly: 42.9% (first wave), 50.0% (second wave), and 61.9% (third wave) less than before the pandemic, respectively. Additionally, they were at a significantly higher risk of incident frailty than those who were not living alone and were socially active (adjusted odds ratio: 2.04 95% confidence interval: 1.01–4.10).
Conclusion
Our findings suggest that older adults who live alone and are socially inactive are more likely to experience incident frailty/disability due to decreased PA during the pandemic. Understanding this mechanism may be crucial for maintaining the health status of older adults.
Freshwater in the Arctic Ocean plays an important role in the regional ocean circulation, sea ice, and global climate. From salinity observed by a variety of platforms, we are able, for the first ...time, to estimate a statistically reliable liquid freshwater trend from monthly gridded fields over all upper Arctic Ocean basins. From 1992 to 2012 this trend was 600±300 km3 yr−1. A numerical model agrees very well with the observed freshwater changes. A decrease in salinity made up about two thirds of the freshwater trend and a thickening of the upper layer up to one third. The Arctic Ocean Oscillation index, a measure for the regional wind stress curl, correlated well with our freshwater time series. No clear relation to Arctic Oscillation or Arctic Dipole indices could be found. Following other observational studies, an increased Bering Strait freshwater import to the Arctic Ocean, a decreased Davis Strait export, and enhanced net sea ice melt could have played an important role in the freshwater trend we observed.
Key Points
Upper Arctic Ocean liquid freshwater trend 1992‐2012: 600±300 km3/yr
Two thirds of the trend was due to changes in salinity, one third due to layer thickness
Covariability of liquid freshwater content and Arctic Ocean Oscillation
By performing a global magnetohydrodynamic (MHD) simulation, we have demonstrated for the first time that an electrojet at the dayside magnetic equator can be reversed and an overshielding condition ...can be established in the inner magnetosphere after substorm onset without northward turning of the interplanetary magnetic field. Near the substorm onset, the plasma pressure is highly enhanced in the inner magnetosphere on the nightside. The Region 2 field‐aligned current diverges from the diamagnetic current on the surface of the dayside extension of the high‐pressure region, which is connected to the ionosphere in the relatively low‐conductivity region a few degrees equatorward of the main auroral oval that is formed as the projection of the plasma sheet. The separation of the equatorward boundary of the auroral region and the equatorward boundary of the Region 2 current results in dusk‐dawn electric fields that generate a counter electrojet (CEJ) at the dayside magnetic equator. Poleward electric fields in a narrow latitudinal width, which may be regarded as subauroral ion drift and subauroral polarization stream, are simultaneously intensified. The dusk‐dawn electric fields may propagate to the inner magnetosphere along a field line as shear Alfvén waves. Then, the inner magnetosphere is completely constrained by the overshielding condition. The intensity and polarity of the CEJ depend largely on at least the ionospheric conductivity that is related to the plasma pressure (probably associated with diffuse aurora). This may explain the observational fact that overshielding does not always occur after onset.
Key Points
Counter equatorial electrojet appears in MHD simulation after substormSeparation between Region 2 current and auroral oval results in overshieldingInner magnetosphere is constrained by the overshielding after substorm
The convection electric field increases during the growth phase of substorms, driving the DP 2 ionospheric currents at high‐to‐equatorial latitudes, intensifying the eastward equatorial electrojet ...(EEJ) on the dayside. During the expansion phase, the electric field is often reversed; i.e., overshielding occurs at subauroral‐to‐equatorial latitudes where the EEJ turns to the westward counterelectrojet (CEJ). In this paper, we show that the HF Doppler sounders detected the eastward overshielding electric field at low latitudes on the nightside simultaneously with the CEJ on the dayside. We also show that the overshielding often occurs during the substorm recovery due to the convection reduction, resulting in a two‐step form in both the dayside CEJ and nightside electric field. The opposite direction of the electric field on the dayside and nightside is consistent with the dusk‐to‐dawn potential electric field associated with the region 2 field‐aligned currents intensified by the substorm. The overshielding electric field was found to drive an eastward electrojet with appreciable magnitude in the nighttime equatorial ionosphere, which in turn causes an equatorial enhancement of the midnight positive bay.
Key Points
Eastward electric field is detected by HF Doppler sounders on the nightside with counterelectrojet on the dayside during substorms
Overshielding electric field drives nighttime equatorial electrojet
Substorm current circuits with region 2 field‐aligned currents are completed through the equatorial electrojet on the dayside and nightside
In this paper, we have evaluated the role of interplanetary magnetic field (IMF) By on the asymmetry of the ring current during the main phase of geomagnetic storms. The mean H variations have been ...calculated using 31 ground magnetic stations over magnetic latitudes of 09–45° following the methodology of Li et al. (2011, https://doi.org/10.1029/2011JA016886). Further, the magnetic local time (MLT) variations in the H component at these stations w.r.t. the mean H were investigated for three cases of geomagnetic storms with varying southward IMF Bz and IMF By conditions. Significant ring current asymmetries were observed during the main phase of geomagnetic storms. The primary role of IMF Bz on the asymmetry of the ring current is observed from these cases. More importantly, the investigation brings out for the first time, the additional role of IMF By in influencing the MLT distribution of ring current observed at ground magnetic stations. Under southward IMF Bz conditions, it is shown based on SuperDARN and AMPERE data that IMF By can alter the MLT distribution of ring current under suitable conditions. The timescales of IMF By also play very important role in determining the asymmetry in the ring current. Under steady convection state, IMF By can rotate the convection cells based on its polarity, which in turn can change the MLT distribution of ring current observed by low‐latitude ground stations. This investigation, thus, brings out the important role of IMF By on the asymmetric MLT distribution of ring current under southward IMF Bz.
Key Points
IMF By plays important role in asymmetry of the ring current observed at ground stations in addition to IMF Bz
SuperDARN convection cells and AMPERE‐derived FACs show the association of IMF By with MLT distribution of the ring current
Under suitable conditions, IMF By can alter the MLT distribution of the ring current
As a generic property, all substances transfer heat through microscopic collisions of constituent particles
. A solid conducts heat through both transverse and longitudinal acoustic phonons, but a ...liquid employs only longitudinal vibrations
. As a result, a solid is usually thermally more conductive than a liquid. In canonical viewpoints, such a difference also serves as the dynamic signature distinguishing a solid from a liquid. Here, we report liquid-like thermal conduction observed in the crystalline AgCrSe
. The transverse acoustic phonons are completely suppressed by the ultrafast dynamic disorder while the longitudinal acoustic phonons are strongly scattered but survive, and are thus responsible for the intrinsically ultralow thermal conductivity. This scenario is applicable to a wide variety of layered compounds with heavy intercalants in the van der Waals gaps, manifesting a broad implication on suppressing thermal conduction. These microscopic insights might reshape the fundamental understanding on thermal transport properties of matter and open up a general opportunity to optimize performances of thermoelectrics.
This paper reports the experiments on the shock standoff distance (SSD) around spheres flying at Mach numbers from slightly below 1.0. Spheres of the same diameter but three different densities were ...launched in a ballistic range by a light-gas gun, and the flow field around each sphere was measured by optical visualization. The purpose of this study is to investigate how projectile deceleration influences the SSD by comparing the results for projectiles of the same shape, size, and Mach number but different densities. The location history of the sphere center is obtained by fitting a formula derived from the equation of motion of a decelerating object, and the history of the instantaneous projectile Mach number is obtained by differentiating this formula.The SSDs of the projectiles with different densities are the same at higher Mach numbers, but different at lower Mach numbers, and the SSD decreases with decreasing projectile density. Seemingly, because projectile deceleration is related to the flow unsteadiness, steady flow cannot be assumed in the present range of Mach number with the different SSDs. At Mach numbers close to one, that of the propagating detached shock wave is higher than that of the flying projectile.
The plasma‐sheet dynamics leading to the substorm onset is analyzed from a global simulation. We calculated three cases, the normal (case 1), reduced magnetosphere‐ionosphere (M‐I) coupling (case 2) ...and reduced tail dissipation (case 3). The normal solution reproduces the thinning, reconnection, tail flow, and the dipolarization in the magnetosphere, and the AU/AL, the initial brightening, the beads, the pre‐onset arc, and the poleward expansion in the ionosphere. Case 2 shows that the M‐I coupling promotes the thinning by evacuating magnetic field from the plasma sheet. Case 3 shows that it is implausible to reproduce the AU/AL of the expansion phase only with numerical dissipation. The projection area of the growth phase plasma sheet is so narrow that the quiet arcs on the high‐latitude side are projected to the lobe. The key point to understand such narrow projection is to consider the origin of the field‐aligned current (FAC). The FAC occurs to transmit motion, and particle precipitation is the consequence. The upward FACs for the quiet arc and initial brightening, which produce the substorm sequence, are generated to transmit enhanced convection from the magnetosphere to the ionosphere. The substorm onset is the transmission of the convection transient. The onset FAC is generated by the near‐earth dynamo. Before the onset, a two‐stage reconnection occurs at the medium‐tail (MTNL) and the near‐earth (NENL) neutral lines through retreating nulls. The accompanying flow explains the model that assumes two causal areas for the onset in the near‐earth and middle tails.
Key Points
The M‐I coupling helps magnetic field transport that causes the plasma sheet thinning in the late growth phase
Two‐step guide‐field reconnection generates complex flow in the plasma sheet reflecting magnetic topology
A dissipation model is required to reproduce the expansion‐phase AU/AL indices in the global simulation
A physical mechanism of the positive ionospheric storms at low latitudes and midlatitudes is presented through multi‐instrument observations, theoretical modeling, and basic principles. According to ...the mechanism, an equatorward neutral wind is required to produce positive ionospheric storms. The mechanical effects of the wind (1) reduce (or stop) the downward diffusion of plasma along the geomagnetic field lines, (2) raise the ionosphere to high altitudes of reduced chemical loss, and hence (3) accumulate the plasma at altitudes near and above the ionospheric peak centered at around ±30° magnetic latitudes. Daytime eastward prompt penetration electric field (PPEF), if it occurs, also shifts the equatorial ionization anomaly crests to higher than normal latitudes, up to approximately ±30° latitudes. The positive ionospheric storms are most likely in the longitudes where the onset of the geomagnetic storms falls in the ionization production dominated morning‐noon local time sector when the plasma accumulation due to the mechanical effects of the wind largely exceeds the plasma loss due to the chemical effect of the wind. The mechanism agrees with the multi‐instrument observations made during the supergeomagnetic storm of 7–8 November 2004, with 18 h long initial phase (IP) and 10 h long main phase (MP). The observations, which are mainly in the Japanese‐Australian longitudes where the MP onset was in the morning (0600 LT, 2100 UT), show (1) strong positive ionospheric storms (in Ne, Nmax, hmax, Global Positioning System–total electron content (GPS‐TEC), and 630 nm airglow intensity) in both Northern and Southern hemispheres started at the morning (0600 LT) MP onset and lasted for a day, (2) repeated occurrence of strong eastward PPEF events penetrated after the MP onset and superposed with westward electric field started before the MP onset, and (3) storm time equatorward neutral winds (inferred from 1 and 2). Repeated occurrence of an unusually strong F3 layer with large density depletions around the equator was also observed during the morning‐noon MP.
A temperature and salinity hydrographic profile climatology is assembled, evaluated for data quality, and analyzed to assess changes of the Bering and Chukchi Sea continental shelves over seasonal to ...century-long time scales. The climatology informs description of the spatial distribution and temporal evolution of water masses over the two shelves, and quantification of changes in the magnitude and throughput of heat and fresh water. For the Chukchi Shelf, linear trend analysis of the integrated shelf heat content over its 1922–2018 period of record finds a significant summer and fall warming of 1.4 °C (0.14 ± 0.07 °C decade−1); over 1990–2018 the warming rate tripled to 0.43 ± 0.35 °C decade−1. In contrast, the Bering Shelf's predominantly decadal-scale variability precludes detection of a water column warming trend over its 1966–2018 period of record, but sea surface temperature data show a significant warming of 0.22 ± 0.10 °C decade−1 over the same time frame. Heat fluxes over 1979–2018 computed by the European Centre for Medium-Range Weather Forecast (ECMWF) ERA5 reanalysis exhibit no record-length trend in the shelf-wide Bering surface heat fluxes, but the Chukchi Shelf cooling season (October–March) has a trend toward greater surface heat losses and its warming season (April–September) has a trend toward greater heat gains. The 2014–2018 half-decade exhibited unprecedented low winter and spring sea-ice cover in the Northern Bering and Chukchi seas, changes that coincided with reduced springtime surface albedo, increased spring absorption of solar radiation, and anomalously elevated water column heat content in summer and fall. Consequently, the warm ocean required additional time to cool to the freezing point in fall. Fall and winter ocean-to-atmosphere heat fluxes were anomalously large and associated with enhanced southerly winds and elevated surface air temperatures, which in turn promoted still lower sea-ice production, extent, and concentration anomalies. Likely reductions in sea-ice melt were associated with positive salinity anomalies on the Southeast Bering Shelf and along the continental slope over 2014–2018. Negative salinity anomalies during 2014–2018 on the central and northern Bering Shelf may be related to a combination of 1) long-term declines in salinity, 2) an increase of ice melt, and 3) a decline of brine production. We hypothesize that freshening on the Bering Shelf and in Bering Strait since 2000 are linked to net glacial ablation in the Gulf of Alaska watershed. We show that the heat engines of both the Bering and Chukchi shelves accelerated over 2014–2018, with increased surface heat flux exchanges and increased oceanic heat advection. During this time, the Chukchi Shelf delivered an additional 5–9 x 1019 J yr−1 (50–90 EJ yr−1) into the Arctic basin and/or sea-ice melt, relative to the climatology. A similar amount of excess heat (60 EJ yr−1) was delivered to the atmosphere, showing that the Chukchi Sea makes an out-sized contribution to Arctic amplification. A conceptual model that summarizes the controlling feedback loop for these Pacific Arctic changes relates heat content, sea ice, freshwater distributions, surface heat fluxes, and advective fluxes.
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