Hanli Liu

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.

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.

Transport of Nitric Oxide in the Winter Mesosphere and Lower Thermosphere

whawkins — Wed, 29 Jan 2025 22:47:48 +0000

Transport of Nitric Oxide in the Winter Mesosphere and Lower Thermosphere whawkins Wed, 01/29/2025 - 15:47

Author:

whawkins

Jan 29, 2025

Geophysical Research Letters: The Earth's thermosphere is heated by the solar extreme ultraviolet (EUV) irradiance and by energetic particle precipitation during solar and geomagnetic storms, and nitric oxide (NO) is one of the most important cooling agent in the thermosphere. The NO level increases rapidly during storm time, making it a natural thermostat for the thermosphere. Moreover, NO is long-lived in polar night region, where it can descend along with the general circulation into the middle atmosphere and effectively destroy ozone. It is therefore an important species for the energy balance of the upper atmosphere and the chemistry and dynamics of the middle atmosphere. However, until recently NO in the winter middle and upper atmosphere is often underestimated in global models that simulate the whole atmosphere system. Newly developed high-resolution whole atmosphere simulations, on the other hand, start to show considerable improvement. Our analysis presented in this study reveals rigorous downward transport in the winter mesosphere and lower thermosphere from the high-resolution model that is not seen in coarse-resolution simulations. The strong downward transport is mainly driven by gravity waves resolved by the high-resolution model.

Nitric oxide (NO) level in the mesosphere and lower thermosphere during polar night is much higher, and compares better with observations in high-resolution WACCM-X simulation. This is seen in the vertical profiles of zonal mean NO at 80N from high-resolution (solid lines) and coarse-resolution (dotted lines) simulations (upper left). Black lines are January averages, and gray lines are daily values. The upper right panel shows the number density of NO from the high-resolution simulations (line contours) and difference between high-resolution and coarse-resolution simulations (contour shades) for January. Non-stippled regions indicate differences that are significant over 95% confidence level according to Student's T-test. This difference stems from the vertical transport due to residual mean circulation and eddy transport. The residual mean vertical wind for January from the coarse resolution (lower left) and high-resolution (lower right) have very different features: at ~100 km (thin horizontal line) the former shows a rather uniform structure with weak flow, while the latter shows large mesoscale flow channels with large vertical velocity.

Tidal control of equatorial vertical ExB drift under solar minimum conditions

whawkins — Tue, 28 May 2024 16:10:15 +0000

Tidal control of equatorial vertical ExB drift under solar minimum conditions whawkins Tue, 05/28/2024 - 10:10

Author:

whawkins

May 28, 2024

Geophysical Research Letters: The vertical ion motion in the equatorial ionosphere plays a key role in the space weather. Satellite observations found that such vertical motion during periods with low solar activity can be quite different from the known climatology, and the cause is not clear. Using a whole atmosphere general circulation model, WACCM-X, we are able to reproduce the pattern of the vertical ion motion similar to that observed during low activity solar cycle periods. By analyzing the model results, we find that the relative significance of the different atmosphere tidal wave components and its variation with solar activity contribute to the solar dependence of the vertical ion motion. The propagating altitudes of tide with 12-hour period, as well as where and when the tidal wind becomes large, are of particular importance.

WACCM-X simulation of monthly averaged vertical ExB drift (a) for June over all local times, and (b) for 0 hour local time over all year under solar minimum conditions.

Assessment of gravity waves from tropopause to thermosphere and ionosphere in high-resolution WACCM-X simulations

whawkins — Tue, 28 May 2024 16:02:09 +0000

Assessment of gravity waves from tropopause to thermosphere and ionosphere in high-resolution WACCM-X simulations whawkins Tue, 05/28/2024 - 10:02

Author:

whawkins

May 28, 2024

Measurement of gravity wave activity in terms of standard deviation of temperature perturbations at (upper left) 78, (upper right) 1.1, (lower left) 1.1×10E−4 and (lower right )1.1×10E−7 hPa, averaged over four UT times (0, 6, 12, and 18 hours) for January. The contour lines are stream functions calculated from the horizontal winds. Contour lines with lighter shades have larger values. Atmosphere flow is tangent to the streamlines and toward the right of the down-gradient direction of the stream functions.

Journal of Advances in Modeling Earth Systems: Small scale waves can be excited from daily weather near the Earth surface. These waves, termed gravity waves, can propagate upward and are thought to influence the middle and upper atmospheric regions. Such effects, however, are difficult to directly quantify by observations and numerical modeling due to their small scales and global presence. To address this challenge, we have developed a high-resolution whole atmosphere model (WACCM-X), which extends from the Earth surface to the upper thermosphere, that can partially resolve the small scale waves. The simulated waves are compared with available observations to verify the model results and to examine how these waves are distributed geographically and over altitudes. The simulations show that wave signatures can be clearly identified in the neutral and the ionized atmosphere, which can have important implications for space weather.

Climate Change in the Thermosphere and Ionosphere From the Early Twentieth Century to Early Twenty‐First Century Simulated by the Whole Atmosphere Community Climate Model—eXtended

whawkins — Fri, 02 Feb 2024 22:11:17 +0000

Climate Change in the Thermosphere and Ionosphere From the Early Twentieth Century to Early Twenty‐First Century Simulated by the Whole Atmosphere Community Climate Model—eXtended whawkins Fri, 02/02/2024 - 15:11

Author:

whawkins

Feb 2, 2024

Five-year zonal mean decadal value differences relative to the 1920s at March equinox (top) and June solstice (bottom) for neutral temperature on the 2.84×10-8 hPa pressure surface a) at ~295 km and e) at ~285 km, neutral density b) at ~377 km and f) at ~395 km, electron density c) at ~377 km and g) at ~395 km, and d) and h) electron column density.

Journal of Geophysical Research, Atmospheres: From seeing lower atmosphere computer climate models run for the past century, we decided to do the same for the upper atmosphere using the Whole Atmosphere Community Climate Model-eXtended (WACCM-X) for the decades from the 1920s to 2010s. In this higher region, the atmosphere is affected strongly by the Sun and removing the Sun’s effect is tricky in previous observation and model studies. We make the Sun’s effect small to see only effects from the Earth’s magnetic field and greenhouse gases. Earlier studies focused on recent decades show effects of greenhouse gas increases on the upper atmosphere but not for the early decades of the past century with greenhouse gas changes from less than 5% increase prior to the space age and the transition to the over 25% increase in the latter half of the 20th century. We cover this entire period and get results like those in studies before, with especially the temperature change matching very well with the greenhouse gas carbon dioxide change. Because WACCM-X performs well over the past century, it will be useful to predict what will happen in the century ahead as greenhouse gases increase and humans make efforts to reverse the increase.

Impacts of gravity waves on the thermospheric circulation and composition

whawkins — Thu, 25 Jan 2024 16:57:15 +0000

Impacts of gravity waves on the thermospheric circulation and composition whawkins Thu, 01/25/2024 - 09:57

Author:

whawkins

Jan 25, 2024

Residual mean meridional wind (a), vertical wind (b) and zonal mean column integrated O/N2 (c) for January from high-resolution (solid lines) and regular resolution WACCM-X simulations.

Geophysical Research Letters: Small-scale waves originating from the lower atmosphere have been shown to propagate into the thermosphere. To study their effects a high-resolution whole atmosphere model has been employed. Using this high-resolution model, which can partially resolve the small-scale waves, we can directly quantify the force exerted by these waves on the general circulation in the thermosphere. We found that such force is strong, and affects the thermospheric circulation in both winter and summer hemisphere. This consequently changes the distribution of important thermospheric species. One measure of the thermospheric composition is the ratio of atomic oxygen and molecular nitrogen, which is an indicator of the relative abundance of atomic and molecular species. This ratio has been grossly over-estimated in previous modeling studies. It is reduced as a result of the circulation change, and is in much better agreement with observations.

Eos Editor's Highlight Features HAO Research

whawkins — Wed, 14 Jun 2023 19:06:23 +0000

Eos Editor's Highlight Features HAO Research whawkins Wed, 06/14/2023 - 13:06

Author:

whawkins

Jun 14, 2023

The research article “Atmospheric and Ionospheric Responses to Hunga-Tonga Volcano Eruption Simulated by WACCM-X”, was selected for featuring as an Editor’s Highlight on Eos.org. Fewer than 2 per cent of papers are selected to be featured in this way.

**Their research article was just published on Eos.org.

Model Output Link Correction:
The Globus connection point for the WACCM-X Hunga-Tonga simulation output, provided in the Data Availability Statement of this GRL paper (https://doi.org/10.1029/2023GL103682) is incorrect. The correct link is: Log in to use Globus Web App.
The QR code is: (See attached png file).

QR code

In addition, see HAO's "Latest Research Highlights".

The upper panels show the exponential growth of the wave amplitude and the vertical structure of the wave in zonal and meridional directions. Distinct wave modes are seen in the vertical wind responses in the mesosphere, lower thermosphere, and upper thermosphere 1.5 hours after the eruption (lower panels).

Atmospheric and Ionospheric Responses to Hunga-Tonga Volcano Eruption Simulated by WACCM-X

whawkins — Tue, 23 May 2023 19:36:16 +0000

Atmospheric and Ionospheric Responses to Hunga-Tonga Volcano Eruption Simulated by WACCM-X whawkins Tue, 05/23/2023 - 13:36

Author:

whawkins

May 23, 2023

Geophysical Research Letters: As one of the most powerful volcano eruptions on record, the Hunga Tonga-Hunga Ha'apai Volcano produces waves that ripple through the atmosphere and near space environment. These wave signals have been recorded by observations from instruments on the ground and from satellites, and they propagate around the Earth multiple times. This event provides a rare opportunity to study the strong and direct connection of the whole atmosphere system. The challenge is for a model to be able to represent the key processes in the whole atmosphere system and to have sufficient spatial and temporal fidelity to gain a realistic global picture of the event. This is achieved in study by using the high-resolution Whole Atmosphere Community Climate Model with thermosphere/ionosphere extension (WACCM-X). The model is able to simulate the global propagation of the waves, and the model results compare favorably with observations from the surface to the thermosphere and ionosphere.

Model Output Link Correction:
The Globus connection point for the WACCM-X Hunga-Tonga simulation output, provided in the Data Availability Statement of this GRL paper (https://doi.org/10.1029/2023GL103682) is incorrect. The correct link is: Log in to use Globus Web App.
The QR code is: (See attached png file).

QR code

Geophysical Research Letters is delighted to highlight this research article on Eos.org. Fewer than 2 per cent of papers are selected to be featured in this way.

This plot shows the surface pressure perturbation (lower layer) and total electron content (TEC) perturbation (upper layer) from the SIMA/WACCM-X simulation of the Hunga-Tonga volcano eruption event.

Hanli Liu

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

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Transport of Nitric Oxide in the Winter Mesosphere and Lower Thermosphere

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Tidal control of equatorial vertical ExB drift under solar minimum conditions

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Assessment of gravity waves from tropopause to thermosphere and ionosphere in high-resolution WACCM-X simulations

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Climate Change in the Thermosphere and Ionosphere From the Early Twentieth Century to Early Twenty‐First Century Simulated by the Whole Atmosphere Community Climate Model—eXtended

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Impacts of gravity waves on the thermospheric circulation and composition

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