Nick Pedatella

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.

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.

Impact of Upward Propagating Migrating Diurnal and Semidiurnal Tides on the Ionosphere-Thermosphere Seasonal Variation

whawkins — Tue, 17 Dec 2024 23:19:49 +0000

Impact of Upward Propagating Migrating Diurnal and Semidiurnal Tides on the Ionosphere-Thermosphere Seasonal Variation whawkins Tue, 12/17/2024 - 16:19

Author:

whawkins

Dec 17, 2024

Seasonal variation of the global mean (a) O/N2, (b) TEC, and (c) neutral density at 350 km in WACCM-X. The results are shown for the control simulation with all tides (black), simulation without the migrating diurnal tide (noDW1, blue), and simulation without the migrating semidiurnal tide (noDW2, red). The results illustrate the impact of the diurnal and semidiurnal tides on the seasonal variation of the thermosphere composition and neutral density as well as the ionosphere electron density.

JGR Space Physics: The Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (WACCM-X) is used to investigate the impact of the upward propagating migrating diurnal (DW1) and semidiurnal (SW2) tides on the seasonal variability in the ionosphere and thermosphere. In the lower thermosphere, the tides induce a westward acceleration that obtains maximum values of 10-20 m/s around solstice. The tidal dissipation also changes the meridional circulation and leads to a ~5K cooling of the lower thermosphere. These changes result in a decrease in atomic oxygen in the lower thermosphere that maximizes during local winter. In the lower thermosphere, the DW1 has a greater impact around December solstice, while the SW2 has a greater impact around June solstice. The DW1 and SW2 induced changes in the lower thermosphere composition lead to changes in the thermosphere column integrated atomic oxygen to molecular nitrogen ratio (O/N2). This leads to a reduction in the thermosphere annual variation at middle to high latitudes. The DW1 and SW2 also reduce the thermosphere neutral mass density. In the ionosphere, the DW1 and SW2 decrease the zonal and diurnal mean total electron content by ~20% globally, which is primarily attributed to the reduction in thermosphere O/N2. The SW2 is found to have a greater influence on the low latitude ionosphere compared to the DW1 due to the SW2 having a greater impact on the equatorial electrodynamics. The results demonstrate that the upward propagating DW1 and SW2 both have significant effects on the ionosphere and thermosphere, including influencing the seasonal variability.

Quasi 6-Day Planetary Wave Oscillations in Equatorial Plasma Irregularities

whawkins — Fri, 05 Apr 2024 16:26:35 +0000

Quasi 6-Day Planetary Wave Oscillations in Equatorial Plasma Irregularities whawkins Fri, 04/05/2024 - 10:26

Author:

whawkins

Apr 5, 2024

WACCM-X Rayleigh-Taylor (R-T) instability growth rate during from January to December 2021 for simulations with (a) lower atmosphere and solar/geomagnetic variability (LA+S/G), (b) only lower atmosphere variability (LA Only), and (c) only solar/geomagnetic variability (S/G Only) simulations. (d-f) Same as (a-c) except for the time period of November 2020 to March 2021. The results show that the day-to-day variability in the R-T instability growth rates is driven by both the lower atmosphere and solar/geomagnetic variations. A quasi-periodic variability is seen in early 2021 that is related to the quasi-six day planetary wave.

Journal of Geophysical Research–Space Physics: N. M. Pedatella, E. Aa, and A. Maute explore the influence of atmospheric planetary waves on the occurrence of irregularities in the low latitude ionosphere is investigated using Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (WACCM-X) simulations and Global Observations of the Limb and Disk (GOLD) observations. GOLD observations of equatorial plasma bubbles (EPBs) exhibit a ∼6-8 day periodicity during January-February 2021. Analysis of WACCM-X simulations, which are constrained to reproduce realistic weather variability in the lower atmosphere, reveals that this coincides with an amplification of the westward propagating wavenumber-1 quasi-six day wave (Q6DW) in the mesosphere and lower thermosphere (MLT). The WACCM-X simulated Rayleigh-Taylor (R-T) instability growth rate, considered as a proxy of EPB occurrence, is found to exhibit a ∼6-day periodicity that is coincident with the enhanced Q6DW in the MLT. Additional WACCM-X simulations performed with fixed solar and geomagnetic activity demonstrate that the ∼6-day periodicity in the R-T instability growth rate is related to the forcing from the lower atmosphere. The simulations suggest that the Q6DW influences the day-to-day formation of EPBs through interaction with the migrating semidiurnal tide. This leads to periodic oscillations in the zonal winds, resulting in periodic variability in the strength of the prereversal enhancement, which influences the R-T instability growth rate and EPBs. The results demonstrate that atmospheric planetary waves, and their interaction with atmospheric tides, can have a significant impact on the day-to-day variability of EPBs.

Influence of Stratosphere Polar Vortex Variability on the Mesosphere, Thermosphere, and Ionosphere

whawkins — Thu, 20 Jul 2023 15:46:09 +0000

Influence of Stratosphere Polar Vortex Variability on the Mesosphere, Thermosphere, and Ionosphere whawkins Thu, 07/20/2023 - 09:46

Author:

whawkins

Jul 20, 2023

WACCM-X daily column integrated O/N2 anomaly between +/- 25 degrees geographic latitude versus the Northern Annular Mode (NAM) at 10 hPa with a lag of eight days. (b) SW2 amplitude anomaly in TEC between 15-25N geomagnetic latitude versus the NAM at 10 hPa with a lag of four days. Results are based on the time period December 15 to March 1.

Journal of Geophysical Research: The Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (WACCM-X) is used to investigate the influence of stratosphere polar vortex variability on the mesosphere, thermosphere, and ionosphere during Northern Hemisphere winter. Based on 40 simulated Northern Hemisphere winters, the mesosphere and lower thermosphere (MLT) residual circulation is found to depend on whether the stratosphere polar vortex is strong or weak. In particular, during weak stratosphere polar vortex time periods, the MLT circulation anomalies are characterized by clockwise and anti-clockwise flow in the Northern and Southern Hemispheres, respectively. Opposite, though weaker, anomalies are found to occur during time periods when the stratosphere polar vortex is strong. The MLT circulation anomalies influence the composition of the lower thermosphere, leading to +/-5% changes in the thermosphere column integrated atomic oxygen to molecular nitrogen ratio (O/N2). Large differences between strong and weak stratosphere polar vortex events are also found to occur in the semidiurnal migrating tide (SW2) in the MLT, which leads to +/- 15-20% differences in the SW2 component of the ionosphere total electron content (TEC) at low latitudes. The WACCM-X simulation results indicate that variability in the stratosphere polar vortex can explain ~30% and ~18 of the quiet time variability in thermosphere O/N2 and the SW2 component of TEC during Northern Hemisphere winter, respectively.

Hemispheric Asymmetry of the Annual and Semiannual Variation of Thermospheric Composition

whawkins — Thu, 18 May 2023 16:00:14 +0000

Hemispheric Asymmetry of the Annual and Semiannual Variation of Thermospheric Composition whawkins Thu, 05/18/2023 - 10:00

Author:

whawkins

May 18, 2023

Daily average O/N2 at 143 km derived from GUVI limb observations for 2003, for the latitude bins of (a) the equatorial (10oS – 10oN); (b) 20oS (10oS – 30oS, red) and 20oN (10oN – 30oN, blue); (c) 40oS (30oS – 50oS, red) and 40oN (30oN – 50oN, blue). The vertical bars show one standard deviations. The solid lines are the corresponding Fourier harmonic fittings (annual and semiannual) to the data.

We examine hemispheric asymmetry of the annual and semiannual variation of the ratio of O and N2 concentrations (O/N2) using observations by the GUVI instrument onboard the TIMED satellite and compare them with WACCM-X model simulations. We found that in the equatorial region, the “equinox peaks” of the observed O/N2 are near the end of March and October, and the two annual lows are near the beginning of July and January. Compared to the equatorial region, in the northern hemisphere (NH) low latitudes, the first “equinox peak” clearly shifts toward the December solstice (DS), whereas in the southern hemisphere (SH) low latitudes, the “equinox peaks” shift toward the June solstice (JS), forming the hemispheric asymmetry characteristics of the annual and semiannual variation. Seasonal variation of O/N2 shows no apparent phase variation with altitude, and the annual and semiannual pattern is consistent from year to year. WACCM-X reproduces the observed annual and semiannual pattern in NH but in SH, it simulates an annual variation instead of the observed annual and semiannual variation. The largest discrepancy occurs near JS in the lower and middle thermosphere: the simulated O density has an annual high near JS in SH; the simulated N2 density has an annual high near JS in NH but a predominant annual low near JS in SH. These are not in the GUVI data. A weaker thermospheric meridional circulation in the winter hemisphere, or a reduced summer-to-winter latitudinal gradient of neutral temperature in WACCM-X simulations would make model-data comparisons more consistent.

Effects of Forcing Uncertainties on the Thermospheric and Ionospheric states during geomagnetic storm and quiet periods

whawkins — Tue, 28 Mar 2023 20:01:15 +0000

Effects of Forcing Uncertainties on the Thermospheric and Ionospheric states during geomagnetic storm and quiet periods whawkins Tue, 03/28/2023 - 14:01

Author:

whawkins

Mar 28, 2023

Longitude-latitude maps of the the STDs of neutral zonal wind computed from WACCM-X ensembles at 4.687*10^-8 hPa pressure level. From top to bottom are results from experiment with lower atmospheric forcing perturbation (ENS EXP2), with magnetospheric forcing perturbation (ENS EXP3), and with both lower atmospheric forcing perturbation and magnetospheric forcing perturbation (ENS EXP1). The first and second columns are the STD of the WACCM-X ensemble at at UT 1200 of 15 and 18 March, respectively. The third column is the difference between the STD at at UT 1200 of 15 and 18 March. The red scale in the third column's subplots means that the STD at UT1200 of March 18 is larger than that at UT1200 of 15 March; the blue scale means that the STD at UT1200 of 18 March is smaller than that at UT1200 of 15 March.

Upper-atmospheric weather prediction is subject to various types of forcing uncertainties. Understanding the sensitivity of the thermosphere and ionosphere to forcing uncertainties under different geomagnetic conditions is critical for space weather predictions. Ensemble simulations of a whole atmospheric model, the National Center for Atmospheric Research Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (WACCM-X), with various kinds of forcing perturbation is used to evaluate the upper atmosphere's response to the uncertainties of different forcings. Two kinds of forcing uncertainties are addressed: the lower atmospheric wave and tide forcing uncertainties and high-latitude electric potential uncertainty. These uncertainties are estimated in different ways and applied to generate forcing perturbations in the WACCM-X. WACCM-X can simulate the upper atmosphere's response to the uncertainties of the lower atmospheric wave and tide forcings related to different lower atmospheric conditions. High-latitude electric potential uncertainty is estimated based on the SuperMag and SuperDARN data through the Assimilative Mapping of Geospace Observations, which is applied to generate the forcing perturbation of high-latitude electric potential in the WACCM-X. The results show that the impact of high-latitude electric potential uncertainty is significant globally during the 2013 St. Patrick's Day storm. The lower atmospheric wave and tide forcing uncertainties result in a global impact on the upper atmosphere in the model. The sensitivity of the upper atmosphere to both uncertainties is approximately the combination of the two individually, though the combined effects are not a linear sum, indicating non-linearities in the ionosphere and thermosphere response to forcing uncertainties.

Nick Pedatella

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

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

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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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Impact of Upward Propagating Migrating Diurnal and Semidiurnal Tides on the Ionosphere-Thermosphere Seasonal Variation

Recent News

Quasi 6-Day Planetary Wave Oscillations in Equatorial Plasma Irregularities

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Influence of Stratosphere Polar Vortex Variability on the Mesosphere, Thermosphere, and Ionosphere

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Hemispheric Asymmetry of the Annual and Semiannual Variation of Thermospheric Composition

Recent News

Effects of Forcing Uncertainties on the Thermospheric and Ionospheric states during geomagnetic storm and quiet periods

Recent News