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1. Predictability of the Mesosphere and Lower Thermosphere During Major Sudden Stratospheric Warmings

   https://doi.org/10.1029/2021GL093716  

   Pedatella, N. M. ; Richter, J. H. ; Edwards, J. ; Glanville, A. A. ( August 2021 , Geophysical Research Letters)

   The predictability of the middle atmosphere during major sudden stratospheric warmings (SSWs) is investigated based on subseasonal hindcasts in the Community Earth System Model, version 2 with the Whole Atmosphere Community Climate Model as its atmospheric component (CESM2[WACCM6]). The CESM2(WACCM6) hindcasts allow for the first comprehensive investigation into the predictability of the mesosphere and lower thermosphere (MLT) during SSWs. Analysis of 14 major SSWs demonstrates that CESM2(WACCM6) hindcasts initialized5–15 days prior to the SSW onset are able to predict the timing of the SSW, though they underestimate the strength of the SSW. Aspects of the MLT variability, such as the mesosphere cooling and enhanced semidiurnal tide, are found to be well predicted. The demonstrated ability to predict MLT variability during SSWs indicates the potential for improved multi‐day space weather forecasting. Improved space weather forecasting may be achieved by using whole atmosphere models that can predict the MLT variability that drives ionosphere‐thermosphere variability during SSWs.

    

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2. Revisiting the Modulations of Ionospheric Solar and Lunar Migrating Tides During the 2009 Stratospheric Sudden Warming by Using Global Ionosphere Specification

   https://doi.org/10.1029/2019SW002184  

   Lin, J. T. ; Lin, C. H. ; Lin, C. Y. ; Pedatella, N. M. ; Rajesh, P. K. ; Matsuo, T. ; Liu, J. Y. ( May 2019 , Space Weather)

   In this study, Global Ionosphere Specification (GIS) based on Gauss‐Markov Kalman filter assimilation of slant total electron content observed from ground‐based global positioning system receivers and space‐based radio occultation instrumentations is applied to investigate the ionospheric day‐to‐day tidal variability during the 2009 stratospheric sudden warming (SSW) period. Including the improved daily three‐dimensional global electron density distribution from GIS enables us to retrieve the daily solar tidal solution by using least squares tidal analysis. We find prominent reductions followed by enhancements in the amplitude of the solar semidiurnal migrating tide (SW2) after the peak warming, with recurrent phase variations occurring at low magnetic latitudes over a period of about 15 days. This is close to the beating period (15.13 day) between SW2 and lunar semidiurnal (M2), thus suggesting the existence of strong M2, and our results demonstrate that the intensification of M2 exists only during the SSW period. Additionally, M2 acts as the key contributor to make the semidiurnal ionospheric perturbations shift toward later local times. Our tidal analyses of daily GIS thus provide evidence for the combined impact of amplitudes and phases of the SW2 and M2 in producing semidiurnal variations in ionosphere during the 2009 SSW.

    

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3. Observation of Scintillation Enhancements and Large‐Scale Structures Within the Equatorial Ionization Anomaly During a Sudden Stratospheric Warming Event

   https://doi.org/10.1029/2022JA030985  

   Valladares, C. E. ; Chen, Y. ‐J. ; Hairston, M. ; Chau, J. L. ; Dhanya, R. ( February 2023 , Journal of Geophysical Research: Space Physics)

   Total electron content (TEC) and L‐band scintillations measured by several networks of GPS and GNSS receivers that operate in South and Central America and the Caribbean region are used to observe the morphology of the equatorial ionization anomaly (EIA), examine the evolution of plasma bubbles, and investigate the enhancement of L‐band scintillations that occurred on February 12 and 13, 2016. A few weak and short magnetic storms developed these days, and a minor sudden stratospheric warming (SSW) event was initiated a few days before. During these unusual conditions, TEC maps reported a split of the otherwise continuous crests of the EIA and the formation of a large‐scale (thousands of kilometers) almost‐circular structure. The western part of the southern crest faded, and a north‐south aligned segment developed near the center of the South American continent, joining the north and south crests of the EIA, forming an anomaly that resembled a closed loop on the eastern side of the continent. Concurrently with the anomaly events, several GPS stations reported increases in the L‐band scintillation index from 0.4 to values greater than 1. We analyzed TEC values from receivers between ±6° from the magnetic equator to identify and follow TEC depletions associated with plasma bubbles when they reach different stations. Although the magnetic activity was moderate (K_p = 3°), we believe that the anomaly redistribution and the scintillation enhancements are not related to a prompt penetration electric field but to enhancing the semidiurnal lunar tide propitiated by the onset of the minor SSW event. We found that depending on the lunar tide phase cycle, the neutral wind's meridional component can augment sub‐km scale irregularities and enhance L‐band scintillations through the wind gradient instability when U·n < 0 or the action of wind gradients (U) within the bubbles. Our observations imply that the SSW event enables prominent changes in the thermosphere wind system at F‐region altitudes.

    

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4. Climatological Westward‐Propagating Semidiurnal Tides and Their Composite Response to Sudden Stratospheric Warmings in SuperDARN and SD‐WACCM‐X

   https://doi.org/10.1029/2020JD032895  

   Zhang, J. ; Limpasuvan, V. ; Orsolini, Y. J. ; Espy, P. J. ; Hibbins, R. E. ( January 2021 , Journal of Geophysical Research: Atmospheres)

   Using the Super Dual Auroral Radar Network observations (clustered around 60°N) and NCAR CESM2.0 extended Whole Atmosphere Community Climate Model nudged with reanalyzes, we examine the climatology of semidiurnal tides in meridional wind associated with the migrating component (SW2) and non‐migrating components of wavenumbers 1 (SW1) and 3 (SW3). We then illustrate their composite response to major sudden stratospheric warmings (SSWs). Peaking in late summer and winter, the climatological SW2 amplitude exceeds SW1 and SW3 except around late Fall and Spring. The winter climatological peak is absent in the model perhaps due to the zonal wind bias at the observed altitudes. The observed SW2 amplitude declines after SSW onset before enhancing ∼10 days later, along with SW1 and SW3. Within the observed region, the simulated SW2 only amplifies after SSW onset, with minimal SW1 and SW3 responses. The model reveals a stronger SW2 response above the observed location, with diminished amplitude before and enhancement after SSW globally. This enhancement appears related to increased equatorial ozone heating and background wind symmetry. The strongest SW1 and SW3 growth occurs in the Southern Hemisphere before SSW. SW2 and quasi‐stationary planetary wave activities are temporally collocated during SSW suggesting that their interactions excite SW1 and SW3. After SSW, the model also reveals (1) semidiurnal‐tide‐like perturbations generated possibly by the interactions between SW2 and westward‐traveling disturbances and (2) the enhancement of migrating semidiurnal lunar tide in the Northern Hemisphere that exceeds non‐migrating tidal and semidiurnal‐tide‐like responses. The simulated eastward‐propagating semidiurnal tides are briefly examined.

    

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

   https://doi.org/10.1029/2023JA031495  

   Pedatella, N. M. ( July 2023 , Journal of Geophysical Research: Space Physics)

   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 (ΣO/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 ΣO/N₂and the SW2 component of TEC during Northern Hemisphere winter, respectively.

    

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