WACCM

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.

Investigation of the physical mechanism of the formation and evolution of equatorial plasma bubbles during a moderate storm on September 17, 2021

whawkins — Wed, 06 Dec 2023 16:34:59 +0000

Investigation of the physical mechanism of the formation and evolution of equatorial plasma bubbles during a moderate storm on September 17, 2021 whawkins Wed, 12/06/2023 - 09:34

Author:

whawkins

Dec 6, 2023

GOLD Namx on September 16-17, 2021. Left panels show the observations on the night of September 16th, while right panels show the observations on the night of September 17th. The red dotted lines represent the magnetic dip equator.

Space Weather: We investigate in detail the occurrence and evolution of ionospheric equatorial plasma bubbles (EPBs) during a moderate storm on September 17th, 2021, using Global-scale Observation of the Limb and Disk (GOLD) observations and Whole Atmosphere Community Climate Model-eXtended (WACCM-X) simulations. GOLD observations show that there were no EPBs on September 16th before the storm but EPBs occurred after the storm commencement on September 17th. The EPBs extended to ~ 30° magnetic latitude. A diagnostic analysis of WACCM-X simulations reveals that the rapid enhancement of prompt penetration electric fields (PPEFs) after the sudden storm commencement is the main reason that triggered the occurrence of the EPBs. Further quantitative analysis shows that vertical plasma drifts, which are enhanced by the PPEF, played a dominant role in strengthening the Rayleigh-Taylor instability, leading to the occurrence of the EPBs and the large latitudinal extension of the EPBs to ~ 30° magnetic latitude during the night of September 17th.

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.

Investigation of the GOLD Observed Merged Nighttime EIA with WACCM-X Simulations during the Storm of November 3–4, 2021

whawkins — Tue, 27 Jun 2023 20:31:42 +0000

Investigation of the GOLD Observed Merged Nighttime EIA with WACCM-X Simulations during the Storm of November 3–4, 2021 whawkins Tue, 06/27/2023 - 14:31

Author:

whawkins

Jun 27, 2023

Geophysical Research Letters: During the storm on November 3 to 4, 2021, the Global-scale Observations of the Limb and Disk (GOLD) mission observed well separated EIA crests post sunset on Nov 3, but merged EIA on Nov 4. We used the Whole Atmosphere Community Climate Model (WACCM-X) to simulate the EIA structures during the two nights. The simulations show two separated post sunset EIA crests on November 3rd but merged post sunset EIA crests on November 4th, which are qualitatively consistent with the GOLD observations. Numerical simulations and Ionospheric Connection Explorer (ICON) neutral wind observations illustrate that the formation of merged EIA crests was due to several hours of downward E × B drifts before and after sunset. Further diagnostic analysis revealed that it was mainly driven by westward electric fields caused by the disturbance dynamo electric field during the recovery phase of the storm.

Nmax observed by GOLD and NmF2 simulated by WACCM-X at 20:10 UT on November 03-04, 2021. The red dotted lines represent the magnetic equator.

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.

Thermospheric and Ionospheric Effects by Gravity Waves from the Lower Atmosphere

whawkins — Tue, 14 Feb 2023 18:31:59 +0000

Thermospheric and Ionospheric Effects by Gravity Waves from the Lower Atmosphere whawkins Tue, 02/14/2023 - 11:31

Author:

whawkins

Feb 14, 2023

Standard deviation of temperature perturbations at (upper left) 78, (upper right) 1.1, (lower left) 1.1x10^-4 hPa and (lower right) 1.1x10^-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.

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 thermsophere, 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 forcing of these waves is found to be strong in the thermosphere. It affects the general circulation and the distribution of important atmospheric composition. The simulations also show that wave signatures can be clearly identified in the neutral and the ionized atmosphere, which can have important implications for space weather.

Investigation of the Post-Sunset Extra Electron Density Peak Poleward of the Equatorial Ionization Anomaly Southern Crest

whawkins — Tue, 18 Oct 2022 16:36:05 +0000

Investigation of the Post-Sunset Extra Electron Density Peak Poleward of the Equatorial Ionization Anomaly Southern Crest whawkins Tue, 10/18/2022 - 10:36

Author:

whawkins

Oct 18, 2022

JGR Space Physics—Xuguang Cai, Liying Qian, Wenbin Wang, Joseph M. McInerney, Han-Li Liu, and Richard W. Eastes

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.

Latitude-longitude distribution of OI 135.6 nm radiance observed by GOLD (top) and NmF2 simulated by WACCM-X (bottom) from 21:55 UT to 22:55 UT on DOY 308 in 2019.

Equinoctial Asymmetry in the Upper Ionosphere: Comparison of Satellite Observations and Models

whawkins — Wed, 05 Oct 2022 17:16:46 +0000

Equinoctial Asymmetry in the Upper Ionosphere: Comparison of Satellite Observations and Models whawkins Wed, 10/05/2022 - 11:16

Author:

whawkins

Oct 5, 2022

JGR Space Phyics—L. Lomidze, D. J. Knudsen, M. Shepherd, J. D. Huba, and A. Maute

SAMI3 simulation results for electron density near noon using TIE-GCM neutral atmosphere as a model input, the bottom panel is the corresponding relative (in %) change for Ne. The wind effect on electron density is shown by the black dashed line and the neutral density by the turquoise line.

The terrestrial ionosphere displays significant equinoctial asymmetry despite the upper atmosphere receiving similar levels of solar ionization energy at a given location and local time in spring and fall during similar solar activity conditions. This intriguing feature is not well understood or modelled, particularly in the upper ionosphere, and causes of the asymmetry are not fully established and quantified. Yet, their study is important to provide better insights into the atmosphere-ionosphere coupling processes. Analysis of Langmuir probe data from ESA’s Swarm satellite at ~525 km altitude reveals that the daytime electron density is larger for all latitudes during March than during September, while the electron temperature shows inverted asymmetry except at low latitudes. Simultaneously obtained neutral density data from Swarm GPS accelerations indicate that the thermosphere is denser during the spring. The asymmetry seen by Swarm electron density observations is also present in electron densities obtained using GPS radio occultation measurements from the COSMIC satellites. Simulations were performed using physics-based ionosphere models (SAMI3, WACCM-X, and TIE-GCM) to determine their ability to produce the observed asymmetry, understand the generation mechanism(s), and establish the relative role of physical drivers. Modeling of the asymmetry by SAMI3 driven with the TIE-GCM neutral atmosphere shows that both neutral density and winds play a critical role, but the density has a greater effect.

On the variability of total electron content over Europe during the 2009 and 2019 Northern Hemisphere SSWs

whawkins — Fri, 02 Sep 2022 16:51:20 +0000

On the variability of total electron content over Europe during the 2009 and 2019 Northern Hemisphere SSWs whawkins Fri, 09/02/2022 - 10:51

Author:

whawkins

Sep 2, 2022

JGR- Space Physics: T. A. Siddiqui, Y. Yamazaki, C. Stolle, A. Maute, J. Lastovicka , I. K. Edemskiy, Z. Mosna.

Sudden Stratospheric Warming events are a polar winter phenomena which mainly occurs in the northern hemisphere. They are associated with large scale changes in the stratosphere which modify significant the solar and lunar tide with a 12 hr period, coupling into the upper atmosphere. One of the observed changes is in middle and low latitudes total electron content (TEC). In this study the variations of the TEC over Europe is investigated during two northern hemisphere SSWs events in 2009 and 2019. TEC variations can be caused by the vertical coupling to lower atmosphere and by geomagnetic forcing. Delineating the two cause of TEC variability in observations is challenging. We investigated the dominant drivers and their respective contributions to TEC changes during both SSW events. We simulate the SSWs using the Whole Atmosphere Community Climate Model eXtended version (WACCM-X) and compare the SSW effect on the semidiurnal solar and lunar tidal variabilities in the mesosphere-lower thermosphere (MLT) region. Further, in order to assess the mechanisms responsible for the TEC variability during the SSWs, we analyze the difference between simulations with the Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIE-GCM) driven by WACCM_X fields at the lower boundary with and without geomagnetic forcing. The TIE-GCM simulations allow us to isolate the geomagnetic and lower atmospheric forcing effects on the TEC. We find that there was a major enhancement in daytime TEC over Europe during the 2019 SSW event, which was predominantly geomagnetically forced (∼80%), while for the 2009 SSW, the major variability in TEC was accounted for by lower atmospheric forcing.

Daily averaged TEC over Europe for TIE-GCM forced at the lower boundary by WACCM-X and (a) S1 with geomagnetic forcing and (b) S2 without geomagnetic forcing, as a function of universal time for the 2019 SSW. The TEC increase attributed to the geomagnetic forcing is illustrated in (c) by the difference of (a) and (b). The filled contour lines in (c) are only plotted when absolute TEC difference exceeds 1 TECU. The dashed black and blue open contour lines mark the contribution of geo- magnetic forcing to the TEC variability at 40 and 80% levels, respectively. The vertical black dashed lines mark the day of PVW.

WACCM

Tidal control of equatorial vertical ExB drift under solar minimum conditions

Recent News

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

Recent News

Investigation of the physical mechanism of the formation and evolution of equatorial plasma bubbles during a moderate storm on September 17, 2021

Recent News

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

Recent News

Investigation of the GOLD Observed Merged Nighttime EIA with WACCM-X Simulations during the Storm of November 3–4, 2021

Recent News

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

Recent News

Thermospheric and Ionospheric Effects by Gravity Waves from the Lower Atmosphere

Recent News

Investigation of the Post-Sunset Extra Electron Density Peak Poleward of the Equatorial Ionization Anomaly Southern Crest

Recent News

Equinoctial Asymmetry in the Upper Ionosphere: Comparison of Satellite Observations and Models

Recent News

On the variability of total electron content over Europe during the 2009 and 2019 Northern Hemisphere SSWs

Recent News