Search

We conducted global simulations of temperature change due to anthropogenic trace gas emissions, which extended from the surface, through the thermosphere and ionosphere, to the exobase. These simulations were done under solar maximum conditions, in order to compare the effect of the solar cycle on global change to previous work using solar minimum conditions. The Whole Atmosphere Community Climate Model‐eXtended was employed in this study. As in previous work, lower atmosphere warming, due to increasing anthropogenic gases, is accompanied by upper atmosphere cooling, starting in the lower stratosphere, and becoming dramatic, almost 2 K per decade for the global mean annual mean, in the thermosphere. This thermospheric cooling, and consequent reduction in density, is less than the almost 3 K per decade for solar minimum conditions calculated in previous simulations. This dependence of global change on solar activity conditions is due to solar‐driven increases in radiationally active gases other than carbon dioxide, such as nitric oxide. An ancillary result of these and previous simulations is an estimate of the solar cycle effect on temperatures as a function of altitude. These simulations used modest, five‐member, ensembles, and measured sea surface temperatures rather than a fully coupled ocean model, so any solar cycle effects were not statistically significant in the lower troposphere. Temperature change from solar minimum to maximum increased from near zero at the tropopause to about 1 K at the stratopause, to approximately 500 K in the upper thermosphere, commensurate with the empirical evidence, and previous numerical models. We conducted global simulations of temperature change due to emissions of trace gases due to human activity, which extended from the surface, throughout the atmosphere, to space. These simulations were done under conditions of high solar activity, in order to compare the effect of the solar cycle to previous work using low solar activity. The Whole Atmosphere Community Climate Model‐eXtended was employed. As in previous work, lower atmosphere warming, due to increasing emissions of greenhouse gases, is accompanied by upper atmosphere cooling, starting in the lower stratosphere, and becoming dramatic, almost 2 K per decade on average, above 100‐km altitude. This upper atmosphere cooling, and consequent reduction in density, is less than the almost 3 K per decade for low solar activity conditions calculated in previous simulations. The dependence of global change on solar activity is due to solar‐driven increases in other gases that cool the thermosphere, so greenhouse gases such as carbon dioxide have less effect. An ancillary result is an estimate of the solar cycle effect on temperatures as a function of altitude, which increased from near zero at about 15 km to approximately 500 K at about 400 km, commensurate with previous work. We performed whole‐atmosphere climate change simulations, for solar maximum conditions, and compared them to previous work for solar minimumIn the thermosphere and ionosphere, anthropogenic climate change at solar maximum is smaller than at solar minimum, in these simulationsThe solar cycle effect on temperature ranges from 500 K in the thermosphere to near zero at the tropopause

We investigate atomic hydrogen (H) variability from the mesopause to the upper thermosphere, on time scales of solar cycle, seasonal, and diurnal, using measurements made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere Ionosphere Mesosphere Energetics Dynamics satellite, and simulations by the National Center for Atmospheric Research Whole Atmosphere Community Climate Model‐eXtended (WACCM‐X). In the mesopause region (85 to 95 km), the seasonal and solar cycle variations of H simulated by WACCM‐X are consistent with those from SABER observations: H density is higher in summer than in winter, and slightly higher at solar minimum than at solar maximum. However, mesopause region H density from the Mass‐Spectrometer‐Incoherent‐Scatter (National Research Laboratory Mass‐Spectrometer‐Incoherent‐Scatter 00 (NRLMSISE‐00)) empirical model has reversed seasonal variation compared to WACCM‐X and SABER. From the mesopause to the upper thermosphere, H density simulated by WACCM‐X switches its solar cycle variation twice, and seasonal dependence once, and these changes of solar cycle and seasonal variability occur in the lower thermosphere (~95 to 130 km), whereas H from NRLMSISE‐00 does not change solar cycle and seasonal dependence from the mesopause through the thermosphere. In the upper thermosphere (above 150 km), H density simulated by WACCM‐X is higher at solar minimum than at solar maximum, higher in winter than in summer, and also higher during nighttime than daytime. The amplitudes of these variations are on the order of factors of ~10, ~2, and ~2, respectively. This is consistent with NRLMSISE‐00. In the mesopause, hydrogen density is higher in summer than in winter, and higher at solar minimum than at solar maximumMSIS exhibits reverse seasonal variation than WACCM and SABER do in the mesopause regionIn the upper thermosphere, H is higher at solar minimum than solar maximum, higher in winter than summer, and also higher at night than day

Using 6 days cross‐track wind data from CHAMP, we investigate the high‐latitude westward wind gradient and reversal that occurs at fixed longitudes (−120° ∼ −30° GLon in the Northern Hemisphere, 150° ∼ 210° GLon in the Southern Hemisphere). The driver of the wind gradient at 60° ∼ 70° GLat and in the noon sector is investigated via TIEGCM. The wind gradient is driven by the combined effects of the Earth's geomagnetic field configuration and the energy deposition from the solar wind. The temporal variations of the neutral wind cell in afternoon sector are critical to the formation of wind gradient. The development of wind gradient is due to the equatorward expansion of the afternoon westward wind cell from the geographic high‐latitudes to 60° ∼ 70° GLat. Whereas the disappearance is associated with the poleward contraction from 60° to ∼70° GLat to higher latitudes. A further diagnostic analysis of model results shows that the primary internal driver of the wind gradient is a balance between ion drag and pressure gradient. In the acceleration phase, ion drag causes the formation of the strong gradient of westward wind, whereas pressure gradient decelerates it. A similar result is found in the deceleration phase. The ion drag is controlled predominantly by both the electron density and the relative motion between the ions and neutrals. At high latitudes, the neutrals often are dragged with ions due to the strong ion drag effects, introducing a similar two‐cell pattern from the convection field into thermospheric winds. The tow‐cell pattern of thermospheric winds is defined as “wind cell” in our work. During the Earth's rotation, the two‐cell pattern of thermospheric winds will vary in latitudes and local times, causing the equatorward expansion or poleward contraction in geographic coordinates. This periodic expansion and contraction each day seem like a breath of Earth's thermosphere‐ionosphere coupled system, as an interesting phenomenon. At 15–21 UT, the strong westward wind cell during the moderate geomagnetic period can arrive at fixed latitudes of 60° ∼ 70° GLat and local times of 10–14 LT, promoting the strong wind gradient at fixed longitudes of −120° ∼ −30° GLon. The formation of the wind gradient is likely related to the temporal variations of the afternoon westward wind cellAt 16 and 18 UT, the wind gradient is controlled by a balance between ion drag and pressure gradientIn both the acceleration and deceleration phases, ion drag (pressure gradient) enhances (prevents) the wind gradient The formation of the wind gradient is likely related to the temporal variations of the afternoon westward wind cell At 16 and 18 UT, the wind gradient is controlled by a balance between ion drag and pressure gradient In both the acceleration and deceleration phases, ion drag (pressure gradient) enhances (prevents) the wind gradient

The Global‐scale Observation of Limb and Disk (GOLD) mission observed distinct post‐sunset, hemispherically asymmetric evolution of the equatorial ionization anomaly between 40° and 50°W on 19 November 2018, with the southern crest shifting poleward but the northern crest remaining in the same latitude region. The Whole Atmosphere Community Climate Model‐eXtended captured this phenomenon. Diagnostic analysis revealed that this asymmetric evolution was due to the hemispheric asymmetry in plasma transport by E×Bdrifts and neutral winds. In the Northern hemisphere, northward neutral wind transport dominated around sunset (20 UT near 45°W), causing the crest to be at lower altitudes and decay faster. After pre‐reversal enhancement (PRE) occurred at 20 UT in the northern hemisphere, E×Band neutral wind transport largely balanced each other, and the crest remained in the same latitude region. In the southern hemisphere EIA crest, PRE occurred around 1 hr later than the one in the north. The northward neutral wind transported the plasma to higher altitudes with less recombination. E×Btransport augmented the neutral wind transport after 21 UT, lifting and pushing the crest poleward. The magnetic field configuration (large declination) and the resultant occurrence time difference in PRE between 40°W and 50°W not only play critical roles in the asymmetric evolution of the two crests, but also makes it possible for this phenomenon to be observed in the GOLD field‐of‐view. A whole atmosphere model from the Earth's surface to the upper thermosphere (∼600 km) quantitively reproduced a hemispherically asymmetric movement of equatorial ionization anomaly (EIA) crests (between 40°W and 50°W; 22–24 UT on 19 November 2018) observed by the airglow measurements on a geo‐stationary satellite. Model results revealed that the neutral winds transported the plasma toward the magnetic equator and higher altitudes with less chemical loss in the southern hemisphere, whereas opposite condition occurred in the northern hemisphere between 19 and 21 UT. Consequently, ionospheric F‐peak height (hmF2) of the EIA in the southern hemisphere was much higher than that in the northern hemisphere. After 20 UT, pre‐reversal enhancement (PRE) appeared in the northern hemisphere. It offsets the transport due to field‐aligned wind in the vertical direction, which made the northern crest stationary. However, PRE appeared 1‐hr later in the southern hemisphere. The transport by E× Bdrifts in the southern EIA region augmented field‐aligned wind transport, lifting the southern EIA crest and shifting it poleward. The local time difference of the PRE occurrence in the two hemispheres drive this hemispherically asymmetric movement of EIA from 22 to 24 UT, which was observed by the geo‐stationary satellite. Whole Atmosphere Community Climate Model‐eXtended simulation captures the Global‐scale Observation of Limb and Disk observed postsunset equatorial ionization anomaly (EIA) asymmetric evolution near 45°W longitudeThe offset of E× Bdrifts and neutral wind transport and strong recombination at lower altitude keep the northern crest at the same latitudePre‐reversal enhancement occurs 1 hr later in the south and augments neutral wind transport to lift the EIA crest and shift it poleward Whole Atmosphere Community Climate Model‐eXtended simulation captures the Global‐scale Observation of Limb and Disk observed postsunset equatorial ionization anomaly (EIA) asymmetric evolution near 45°W longitude The offset of E× Bdrifts and neutral wind transport and strong recombination at lower altitude keep the northern crest at the same latitude Pre‐reversal enhancement occurs 1 hr later in the south and augments neutral wind transport to lift the EIA crest and shift it poleward

The Global‐scale observation of limb and disk mission observed an extra electron density (Ne) peak after sunset at approximately 30°S near 40°W on 4 November 2019, which is poleward and immediately next to the southern equatorial ionization anomaly (EIA) crest. This Ne peak is different from previously reported mid‐latitude peaks that occur at all local times. The Whole Atmosphere Community Climate Model‐eXtended captures this phenomenon. Model diagnostic analysis reveals that the decrease of Ne and hmF2 between 15° and 25°S makes Ne near 30°S appear as an extra density peak relative to the southern EIA crest. Transport by poleward meridional wind decreases Ne between 15° and 25°S. Moreover, the upward E × B drifts due to pre‐reversal enhancement lift the plasma between the dip equator and 15°S but do not affect Ne much between 15° and 25°S with a low drift speed. Comparison with days without the extra peak shows the importance of E × B drift latitudinal variations on the extra peak formation. This study provides new insights into the dynamic variability of the nighttime ionosphere. A whole atmosphere model from the Earth's surface to the upper thermosphere (approximately 600 km) captures qualitatively an extra electron density (Ne) peak poleward of the southern equatorial ionization crest near sunset (approximately 30°S, 40°W on 4 November 2019) observed by a far ultraviolet (FUV) instrument onboard a geostationary satellite. Model diagnostic analysis reveals that the depletion of Ne and the decrease of the Ne peak altitude (hmF2) between 15° and 25°S makes the Ne between 25° and 40°S to appear as an extra peak relative to the southern EIA crest near 15°S. The transport by the poleward meridional wind decreases Ne between 15° and 25°S. Moreover, the upward plasma drift lifts the plasma between the dip equator and 15°S but does not affect Ne much between 15° and 25°S due to the low drift speed. Consequently, Ne between 15° and 25°S decreases. Comparison with days without the extra peak also shows that the latitudinal variations of upward plasma drift play an important role in the formation of the extra peak. In summary, the observed extra Ne peak in the southern hemisphere is caused by the plasma transport by poleward meridional winds and weak upward drifts. WACCM‐X captures the GOLD observed sunset extra NmF2 peak at approximately 30°S, 40°W that is in the poleward of the southern EIA crest on 4 November 2019NmF2 depletion between 10° and 25°S separates the southern crest, causing the appearance of an extra peak relative to the southern crestTransport due to the poleward meridional wind with a weak vertical E × B drift (approximately 1 m/s), decrease NmF2 and hmF2 between 15° and 25°S WACCM‐X captures the GOLD observed sunset extra NmF2 peak at approximately 30°S, 40°W that is in the poleward of the southern EIA crest on 4 November 2019 NmF2 depletion between 10° and 25°S separates the southern crest, causing the appearance of an extra peak relative to the southern crest Transport due to the poleward meridional wind with a weak vertical E × B drift (approximately 1 m/s), decrease NmF2 and hmF2 between 15° and 25°S

Previous studies have established the importance of the increasing greenhouse gas (GHG) concentrations in causing trends in the thermosphere and ionosphere (T‐I). Recent work indicates that the changing Earth's magnetic field is also important. We conduct whole atmosphere model simulations to examine T‐I trends driven by these two drivers and their relative importance. We found that, (1) trends in the T‐I, driven by either of the two drivers, exhibited significant latitudinal and longitudinal variability; (2) in the thermosphere, trends were predominantly driven by the GHG driver except that the magnetic field driver played a small role in the neutral temperature trend (∼25%) in some regions mainly in the longitude sector ∼120°W–20°E. The magnetic field driver played a more important role in the ionosphere in the longitude sector ∼120°W–20°E. In this longitude sector, the two drivers were comparable in driving the trends of hmF2, NmF2, and electron temperature; the relative importance of the two drivers to the ion temperature trend additionally depends on altitude, with the GHG driver being the dominant driver at lower altitudes (∼200–320 km), and the two drivers becoming comparable above; (3) although the magnetic field driver is important in the longitude sector ∼120°W–20°E, it drove both negative and positive trends in roughly equal amounts, consequently, its contributions to the global average trends in the T‐I are negligible. The magnetic field are as important as CO2in driving ionospheric trends in the longitude sector 120°W–20°EThe relative importance of the two trend drivers to ion temperature trend additionally depends on altitudeGlobal‐mean trends in the thermosphere and ionosphere are almost entirely driven by CO2, with the magnetic field playing a negligible role The magnetic field are as important as CO2in driving ionospheric trends in the longitude sector 120°W–20°E The relative importance of the two trend drivers to ion temperature trend additionally depends on altitude Global‐mean trends in the thermosphere and ionosphere are almost entirely driven by CO2, with the magnetic field playing a negligible role