Geospace Community Modeling

Influence of the Stratospheric Quasi-Biennial Oscillation on the Seasonal Variation in the Mesosphere and Lower Thermosphere Based on a Long-Term Reanalysis JAWARA

whawkins — Thu, 08 Jan 2026 16:43:32 +0000

Influence of the Stratospheric Quasi-Biennial Oscillation on the Seasonal Variation in the Mesosphere and Lower Thermosphere Based on a Long-Term Reanalysis JAWARA whawkins Thu, 01/08/2026 - 09:43

Author:

whawkins

Jan 8, 2026

Journal of the Atmospheric Sciences: In the equatorial region, the influence of the stratospheric quasi-biennial oscillation (QBO) extends into the mesosphere and lower thermosphere (MLT) region. This work (D. Koshin and K. Sato) presents the characteristics of this response to the QBO in terms of the semiannual oscillations (SAOs) around the stratopause and the mesopause, and the tides, using the long-term global reanalysis for the whole neutral atmosphere over 19 years of 2004–23. The results indicate that the response is observed at a wide height region of the mesosphere and lower thermosphere, with dominance in two separate height regions, at altitudes around 80 and 100 km. The lower one is observed as a vertical shift of the easterly shear during equinoxes, which can be explained by the difference in the QBO phase-dependent filtering of waves in the stratosphere. The upper one is observed as a stronger easterly during the QBO westerly phase at 10 hPa, in all seasons, associated with larger amplitude and the forcing due to the migrating diurnal tide (DW1). The DW1 propagation latitude region, i.e., the region where the sum of relative and planetary vorticity is equal to or smaller than the frequency of DW1, is relatively wider in the middle mesosphere during the QBO westerly phase. These results suggest that there is a two-step mechanism: first, direct modulation of the upper-mesospheric zonal wind by the QBO through selective wave transmission, and second, the variation in the lower thermospheric zonal wind through selective DW1 transmission due to modulated vorticity.

Time and height section of the monthly mean zonal-mean zonal wind in the latitudinal range of 108S–108N for (a) climatology, (b) stratosphere quasi biennial oscillation (SQBO) easterly composite, (c) SQBO westerly composite, and (d) the difference (i.e., SQBO easterly2 SQBO westerly). Contour intervals are 10 m s21 and 5 m s21 in (d). (e) The annual mean of the difference and its standard deviation. The results show the QBO in the stratosphere can have significant influence on the mesosphere and lower thermosphere altitudes.

Contribution of Gravity Waves to the Lower Thermospheric Winter-to-summer Meridional Circulation in High-resolution WACCM-X

whawkins — Wed, 10 Dec 2025 20:45:29 +0000

Contribution of Gravity Waves to the Lower Thermospheric Winter-to-summer Meridional Circulation in High-resolution WACCM-X whawkins Wed, 12/10/2025 - 13:45

Author:

whawkins

Dec 10, 2025

Journal of Geophysical Research, Atmospheres: In the lower thermosphere, there is a large circulation from the winter polar region to the summer polar region at an altitude around 120 km. This study analyzed the role of gravity waves contributing to this circulation using output from a high-resolution simulation. In the winter middle atmosphere, gravity waves with eastward phase speeds are generated around the polar vortex and propagate into the lower thermosphere. Gravity waves are typically assumed to originate in the troposphere and are thought to be unable to propagate above the strong winds in the mesosphere. This study highlights the importance of gravity wave generation in the middle atmosphere and suggests a method for improving parameterized gravity waves. Additionally, the vertical structure of the zonal mean zonal wind is important through the selective filtering of gravity waves. In the summer hemisphere, semidiurnal tidal forcing largely contributes to the lower thermospheric circulation, as do gravity waves. Thus, the lower thermospheric circulation is driven by gravity waves generated in the mesosphere and filtered in the upper mesosphere, as well as by the semidiurnal tide.

Time-latitude sections of (a) the meridional component of the residual mean circulation and (b) the vertical momentum flux divergence for small scale waves based on high-resolution (0.25 degree) WACCM-X simulations. The results illustrate the role of small scale wave forcing on driving the interhemisphere circulation in the lower thermosphere, including its seasonal variation.

Local Time Variability of Gravity Wave Activity Revealed by SABER Temperature Observations

whawkins — Wed, 10 Dec 2025 20:37:23 +0000

Local Time Variability of Gravity Wave Activity Revealed by SABER Temperature Observations whawkins Wed, 12/10/2025 - 13:37

Author:

whawkins

Dec 10, 2025

Geophysical Research Letters: We investigate diurnal variability in gravity wave activity, which is an indication of the interaction between gravity waves and tides. We use satellite observations covering almost all solar local times, to estimate the potential energy of gravity waves at each local time. In the equatorial region between 15°S and 15°N, a clear diurnal cycle is observed. This structure is attributed to the static stability associated with the diurnal tide. In the midlatitudes, at 15–60°N and 15–60°S, a semidiurnal variation is observed at altitudes above 90 km. This structure can also be explained by the static stability associated with the semidiurnal tide. These results are generally consistent with previous ground-based observations, although the spatial coverage of ground-based observations is limited. Thus, this study provides a global view of the interaction between gravity waves and tides in the real atmosphere.

Local time-height section of the gravity wave potential energy derived from TIMED/SABER observations. The results are averaged for 50–60°S, 20–30°S, 5°S–5°N, 20–30°N, and 50–60°N (from left to right) for NDJ, FMA, MJJ, and ASO (from top to bottom). These results illustrate the significant local time variation in the gravity wave potential energy, and how it varies with season and latitude.

Quantifying the Impact of Solar Irradiance Uncertainty on Thermosphere-Ionosphere Variability Using Ensemble Forecasts

whawkins — Wed, 10 Dec 2025 18:11:52 +0000

Quantifying the Impact of Solar Irradiance Uncertainty on Thermosphere-Ionosphere Variability Using Ensemble Forecasts whawkins Wed, 12/10/2025 - 11:11

Author:

whawkins

Dec 10, 2025

Histogram of the normalized model–data difference (Ai) for dayside Swarm neutral density. The grey histogram shows Ai computed from the WACCM-X ensemble using the new method (EXP 3). The green and red histograms represent Ai computed using the old method (EXP 1 and EXP 2). The blue histogram shows Ai computed with the new method, but with doubled spread (EXP 4). The top row presents the Ai distributions for Swarm-A, and the bottom row shows those for Swarm-C. Blue dashed lines indicate the ±3-standard-deviation thresholds.

Space Weather: This study investigates the sensitivity of the thermosphere and ionosphere to variations in solar spectral irradiance. Using data from the SDO and SORCE missions collected between 2010 and 2018, we quantified the variability and uncertainty of solar spectral irradiance across wavelengths from 0.1 to 190 nm and developed a data-driven method to generate perturbed versions of the irradiance. These perturbations were used to drive ensemble simulation experiments conducted during the 2021/2022 winter to assess sensitivity in the thermosphere and ionosphere. In addition to the experiment using statistically derived perturbations, three more ensemble experiments driven by different perturbation methods were also performed.
Results show that both neutral temperature and electron density are highly sensitive to uncertainty in solar spectral irradiance, especially above 200 km altitude. Electron density is particularly influenced by soft X-ray variability in the lower ionosphere. Comparisons with Swarm, ICON, and COSMIC-2 satellite observations confirm the performance of ensemble simulation experiments on capturing the realistic thermospheric and ionospheric variability. Among the experiments, the one driven by statistically derived perturbations produces ensemble spreads that best match the observed variability. This experiment shows good agreement with all three datasets, while the others tend to overestimate or underestimate the variability.
This work highlights the importance of accounting for uncertainty in external solar energy input in space weather models and demonstrates the value of data-informed ensemble simulations in improving the accuracy and reliability of thermosphere and ionosphere forecasts.

The Long-term Trend of Thermospheric Compositions from Whole Atmospheric Simulation and Satellite Observation

whawkins — Tue, 11 Nov 2025 20:32:51 +0000

The Long-term Trend of Thermospheric Compositions from Whole Atmospheric Simulation and Satellite Observation whawkins Tue, 11/11/2025 - 13:32

Author:

whawkins

Nov 11, 2025

JGR space physics: This study examines the long-term trend of column-integrated atomic oxygen to molecular nitrogen ratio, O/N2, in the upper atmosphere and investigates the cause of this long-term trend in O/N2. We first validate the feasibility of using a physics-based model for a long-term climate reanalysis by applying a model-data comparison between 2002 and 2018. O/N2 simulated by NSF NCAR's Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X) and measured by Global Ultraviolet Imager (GUVI) aboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission is used to determine the long-term trend of O/N2 from 2002 to 2018 and validate the model result. The model and data show good agreement after removing the impact of solar irradiance and geomagnetic activity using a least-squares fitting method, revealing a decreasing trend of O/N2 of about -0.54% per decade relative to the O/N2 in 2018 in the model and about -0.45% per decade in data along the satellite orbit during the period between 2002 and 2018. A decreasing trend of global O/N2 of about -0.70% per decade is found in the model between 1960 and 2018. After that, four WACCM-X long-term simulations are performed from 1960 to 2018 to identify the cause of the decreasing trend of O/N2. The results show that this decreasing trend is mainly caused by the increase in greenhouse gas concentrations.

O/N2 measured by TIMED/GUVI and simulated by WACCM-X Case4 and their linear trends. (a) Black and grey lines are the O/N2 data derived from TIMED/GUVI and simulated by WACCM-X, respectively. (b) Dark and light green lines are the fitting curves of the black and grey lines in (a) using the least-squares fitting method with an equation that includes the annual, semi-annual, F10.7 index, and Ap index variations. (c) The blue line is the residual term of TIMED/GUVI O/N2 by subtracting the dark green line from the black line, while the cyan line is the residual term of WACCM-X O/N2 by subtracting the light green line from the grey line. (d) Red and magenta lines are the fitting results of blue and cyan lines using the least-squares fitting method with a linear equation, respectively.

Seasonal and Interannual Variation of the Interhemispheric Coupling during the Austral Winter in WACCM6

whawkins — Tue, 24 Jun 2025 18:49:31 +0000

Seasonal and Interannual Variation of the Interhemispheric Coupling during the Austral Winter in WACCM6 whawkins Tue, 06/24/2025 - 12:49

Author:

whawkins

Jun 24, 2025

Results showing the interhemisphere coupling simulated by WACCM6 in July, August, and September. Latitude-height sections of (top) temperature (color) and zonal wind (contour), (middle) temperature (color) and zonal wind (contour) anomaly, and (bottom) stream function of the residual mean circulation composites during cold equatorial stratosphere events averaged over Day = 0 to 4. Results for July (left), August (middle), and September (right) are shown.

Journal of Geophysical Research–Atomspheres: This paper describes the coupling between the winter stratosphere in the Southern Hemisphere and the northern upper mesosphere as seen in a long-term whole atmosphere model simulation. Characteristics in the winter hemisphere were common for events in July, August, and September. However, there were several differences in the summer hemisphere. First, the modulation of the zonal wind and gravity wave forcing is opposite between the early season (July and August) and the late season (September) due to the difference in the background atmosphere. Second, an interannual variation is observed in the altitude of the warming in the summer polar region, with warmings occurring either above or below 100 km. The warming that appears in the upper mesosphere below 100 km altitude is similar to that in previous studies. On the other hand, the warming that appears in the lower thermosphere above 100 km is explained by an additional mechanism through the modulation of the circulation in the lower thermosphere, which has an opposite direction to that in the mesosphere. This interannual variation is associated with the phase of the intraseasonal oscillation in the equatorial mesosphere and lower thermosphere.

Impact of increasing greenhouse gases on the ionosphere and thermosphere response to a May 2024-like geomagnetic superstorm

whawkins — Tue, 24 Jun 2025 18:38:29 +0000

Impact of increasing greenhouse gases on the ionosphere and thermosphere response to a May 2024-like geomagnetic superstorm whawkins Tue, 06/24/2025 - 12:38

Author:

whawkins

Jun 24, 2025

CESM(WACCM-X) (a) absolute global mean thermosphere neutral density, (b) storm-time change in global mean thermosphere neutral density, and (c) relative storm-time change in global mean thermosphere neutral density. (d) Geomagnetic Kp index used as forcing in CESM(WACCM-X). The CESM(WACCM-X) neutral density results are at an altitude of 350 km, and the storm-time changes are calculated relative to the average values on May 8-9 in each scenario. The storm is simulated in years 2016, 2040, 2061, and 2084, which have surface CO2 values of 403, 500, 652, and 918 ppmv.

Geophysical Research Letters: Geomagnetic storms lead to large changes in the Earth’s upper atmosphere (ionosphere and thermosphere) that can have adverse effects on technological systems, such as GPS positioning and orbits of satellites in low-Earth orbit (200-2000 km). It is now understood that increases in greenhouse gas concentrations result in a decrease in the thermosphere neutral density. This is primarily due to CO2 being a radiative cooler at high altitudes, leading to a reduction in temperatures in the mesosphere and thermosphere, and a contraction of the upper atmosphere. The ionosphere is also impacted by changes in CO2. The present study is focused on understanding how changes in the background state of the upper atmosphere due to increases in CO2 alter the response of the ionosphere and thermosphere to geomagnetic storms. Using a coupled Earth system model that includes an atmospheric component that extends to the ionosphere and thermosphere, the response of the upper atmosphere to a geomagnetic superstorm is simulated for different levels of CO2 concentrations. It is found that increasing levels of CO2 generally result in a weaker response of the ionosphere and thermosphere to geomagnetic storms in absolute terms, while their relative responses enhance at higher CO2 levels.

Multifluid equations for MHD

whawkins — Fri, 23 May 2025 15:19:59 +0000

Multifluid equations for MHD whawkins Fri, 05/23/2025 - 09:19

Author:

whawkins

May 23, 2025

JGR Space Physics: The ionized atoms in near-Earth space, the plasma, consist of a number of species including hydrogen, helium, and oxygen in various states of ionization. Hydrogen is usually the predominant component, but other species can play an important role in the dynamics of space plasmas. Computer simulations of these plasmas, including the effects of the magnetic and electric fields, have been quite successful at describing the near-Earth space. However, in general, they have rarely included any ion species other than hydrogen. This paper describes a multifluid approach that makes it possible to include other ion species assuming the ions are tightly bound to magnetic field lines. In this case, the ions all move together perpendicular to the local magnetic field but are free to move individually along the field direction. This work shows how changes in the magnetic field direction can act to accelerate ions along the field, much like a jai alai ball being thrown with a cesta. The work also shows how plasma waves behave in such a multifluid environment. Finally, the paper presents results of a super-computer simulation of the near-Earth space, modeling the behavior of different plasma fluids and their interactions during a geomagnetic storm.

Overview image of the multifluid MAGE application with a separate fluid for plasma of plasmaspheric origin. All panels are shown in the equatorial plane of the magnetosphere and panels (b-e) correspond to the marked box in panel (a). Shown are: the residual, i.e., non-dipolar component, of the northward magnetic field (a); the density and temperature of fluid~1 (b and c); and the density and temperature of fluid~2 (d and e).

Evaluating F10.7 and F30 radio fluxes as long-term solar proxies of energy deposition in the thermosphere

whawkins — Tue, 25 Feb 2025 16:24:07 +0000

Evaluating F10.7 and F30 radio fluxes as long-term solar proxies of energy deposition in the thermosphere whawkins Tue, 02/25/2025 - 09:24

Author:

whawkins

Feb 25, 2025

Annale Geophsicae: We use model simulations and observations to examine how well the F10.7 and F30 solar radio fluxes have represented solar forcing in the thermosphere during the last 60 years of weakening solar activity. We found that increased saturation of radio fluxes during the last two extended solar minima leads to an overestimation of solar energy deposition, which manifests as a change in the linear relation between thermospheric parameters and F10.7. On the other hand, the linear relation between thermospheric parameters and F30 remains nearly the same throughout the whole studied period because of a recently found relative increase of F30 with respect to F10.7. This explains the earlier finding that F30 correlates better with several ionospheric and thermospheric parameters than F10.7 during recent decades. We note that continued evaluation is needed to see how well F10.7 and F30 will serve as solar proxies in the future when solar activity may start increasing toward the next grand maximum.

Averaged mass density at 400 km. Black: mass density derived from satellite drag data; blue: simulated mass density using F10.7 as a solar EUV proxy; red: simulated mass density using F30 as a solar EUV proxy. (b) Solid black: mass density ratio of the simulated density using F10.7 as a solar EUV proxy to the density derived from satellite drag; dotted red line: linear fit to the mass density ratio from 1967–1996; dotted black line: linear fit to the mass density ratio from 1967–2019; blue: daily F10.7 for reference. (c) Same as panel (b) but for the case with the simulated mass density using F30 as a solar EUV proxy.

The Formation Mechanism of Merged EIA During a Storm on 4 November 2021

whawkins — Wed, 05 Feb 2025 16:29:40 +0000

The Formation Mechanism of Merged EIA During a Storm on 4 November 2021 whawkins Wed, 02/05/2025 - 09:29

Author:

whawkins

Feb 5, 2025

Nmax observed by GOLD (a, b) and NmF2 simulated by WACCM-X (c, d) at 20:10 UT on November 03-04, 2021. The red dotted lines represent the magnetic equator. The black dotted lines represent the 0° longitude. The temporal variations of NmF2 at the 0° longitude (40°S - 40°N latitude) from 9:00 UT and 24:00 UT, simulated by WACCM-X, for November 3rd (e) and 4th (f); The corresponding temporal variations of the peak distance of the South and North EIA crests in (e) and (f), for November 3rd (g) and 4th (h).

JGR-Space Physics: In this study, we conduct an in-depth analysis of Whole Atmosphere Community Climate Model-eXtended (WACCM-X) simulations to examine physical mechanisms of the formation and evolution of an equatorial ionization anomaly (EIA) merging phenomenon during a storm on November 4th, 2021. A quantitative analysis reveals that the rapid decay of the EIA crests at their poleward sides at altitudes of ~200-250 km plays a crucial role in the EIA merging during that day. This rapid decay is due to the fast recombination at low altitudes (~200-250 km) as the plasma are transported downward by the westward disturbance dynamo electric field (DDEF) and poleward neutral winds during the storm. The results suggested EIA-merging is not merely northern and southern EIA crests moving together, but it involves a crucial rapid decay of the EIA crests at their poleward sides that descended to low altitudes (rapid recombination, ~200-250 km), driven by regional electric fields and neutral winds. This study plays a crucial role in our understanding of the evolution and formation of the merged EIA on November 4th, 2021 during the storm.

Geospace Community Modeling

Influence of the Stratospheric Quasi-Biennial Oscillation on the Seasonal Variation in the Mesosphere and Lower Thermosphere Based on a Long-Term Reanalysis JAWARA

Recent News

Contribution of Gravity Waves to the Lower Thermospheric Winter-to-summer Meridional Circulation in High-resolution WACCM-X

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Local Time Variability of Gravity Wave Activity Revealed by SABER Temperature Observations

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Quantifying the Impact of Solar Irradiance Uncertainty on Thermosphere-Ionosphere Variability Using Ensemble Forecasts

Recent News

The Long-term Trend of Thermospheric Compositions from Whole Atmospheric Simulation and Satellite Observation

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Seasonal and Interannual Variation of the Interhemispheric Coupling during the Austral Winter in WACCM6

Recent News

Impact of increasing greenhouse gases on the ionosphere and thermosphere response to a May 2024-like geomagnetic superstorm

Recent News

Multifluid equations for MHD

Recent News

Evaluating F10.7 and F30 radio fluxes as long-term solar proxies of energy deposition in the thermosphere

Recent News

The Formation Mechanism of Merged EIA During a Storm on 4 November 2021

Recent News