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- ItemEvidence for the In‐Situ Generation of Plasma Depletion Structures Over the Transition Region of Geomagnetic Low‐Mid Latitude(Hoboken, NJ : Wiley, 2021) Sivakandan, M.; Mondal, S.; Sarkhel, S.; Chakrabarty, D.; Sunil Krishna, M.V.; Upadhayaya, A.K.; Shinbori, A.; Sori, T.; Kannaujiya, S.; Champati Ray, P.K.On a geomagnetic quiet night of October 29, 2018, we captured an observational evidence of the onset of dark band structures within the field-of-view of an all-sky airglow imager operating at 630.0 nm over a geomagnetic low-mid latitude transition region, Hanle, Leh Ladakh. Simultaneous ionosonde observations over New Delhi shows the occurrence of spread-F in the ionograms. Additionally, virtual and peak height indicate vertical upliftment in the F layer altitude and reduction in the ionospheric peak frequency were also observed when the dark band pass through the ionosonde location. All these results confirmed that the observed depletions are indeed associated with ionospheric F region plasma irregularities. The rate of total electron content index (ROTI) indicates the absence of plasma bubble activities over the equatorial/low latitude region which confirms that the observed event is a mid-latitude plasma depletion. Our calculations reveal that the growth time of the plasma depletion is ∼2 h if one considers only the Perkins instability mechanism. This is not consistent with the present observations as the plasma depletion developed within ∼25 min. By invoking possible Es layer instabilities and associated E-F region coupling, we show that the growth rate increases roughly by an order of magnitude. This strongly suggests that the Cosgrove and Tsunoda mechanism may be simultaneously operational in this case. Furthermore, it is also suggested that reduced F region flux-tube integrated conductivity in the southern part of onset region created conducive background conditions for the growth of the plasma depletion on this night.
- ItemMulti‐Point Measurements of the Plasma Properties Inside an Aurora From the SPIDER Sounding Rocket(Hoboken, NJ : Wiley, 2021) Giono, Gabriel; Ivchenko, Nickolay; Sergienko, Tima; Brändström, UrbanThe Small Payloads for Investigation of Disturbances in Electrojet by Rockets (SPIDER) sounding rocket was launched on February 2nd, 2016 (21:09 UT), deploying 10 free falling units (FFUs) inside a westward traveling auroral surge. Each FFUs deployed spherical electric field and Langmuir probes on wire-booms, providing in situ multi-point recordings of the electric field and plasma properties. The analytical retrieval of the plasma parameters, namely the electron density, electron temperature and plasma potential, from the Langmuir probe measurements was non-trivial due to sheath effects and detailed explanation are discussed in this article. An empirical assumption on the sheath thickness was required, which was confirmed by simulating the plasma environment around the FFU using the Spacecraft Plasma Interaction Software (SPIS). In addition, the retrieved electron density and temperature are also in agreement with the simultaneous incoherent scatter radar measurements from the EISCAT facility. These two independent confirmations provided a good level of confidence in the plasma parameters obtained from the FFUs, and events observed during the flight are discussed in more details. Hints of drift-wave instabilities and increased currents inside a region of enhanced density were observed by the FFUs.
- ItemRadar Observation of Extreme Vertical Drafts in the Polar Summer Mesosphere(Hoboken, NJ : Wiley, 2021) Chau, J.L.; Marino, R.; Feraco, F.; Urco, J.M.; Baumgarten, G.; Lübken, F.‐J.; Hocking, W.K.; Schult, C.; Renkwitz, T.; Latteck, R.The polar summer mesosphere is the Earth's coldest region, allowing the formation of mesospheric ice clouds. These ice clouds produce strong polar mesospheric summer echoes (PMSE) that are used as tracers of mesospheric dynamics. Here, we report the first observations of extreme vertical drafts (+/-50 ms [hoch]-1) in the mesosphere obtained from PMSE, characterized by velocities more than five standard deviations larger than the observed vertical wind variability. Using aperture synthesis radar imaging, the observed PMSE morphology resembles a solitary wave in a varicose mode, narrow along propagation (3–4 km) and elongated (>10 km) transverse to propagation direction, with a relatively large vertical extent (~13 km). These spatial features are similar to previously observed mesospheric bores, but we observe only one crest with much larger vertical extent and higher vertical velocities.
- ItemMesospheric Q2DW Interactions With Four Migrating Tides at 53°N Latitude: Zonal Wavenumber Identification Through Dual‐Station Approaches(Hoboken, NJ : Wiley, 2021) He, Maosheng; Forbes, Jeffrey M.; Li, Guozhu; Jacobi, Christoph; Hoffmann, PeterMesospheric winds from two longitudinal sectors at 53°N latitude are combined to investigate quasi-two-day waves (Q2DWs) and their nonlinear interactions with tides. In a summer 2019 case study, we diagnose the zonal wavenumber m of spectral peaks at expected frequencies through two dual-station approaches, a phase differencing technique (PDT) on individual spectral peaks and a least squares procedure on family batched peaks. Consistent results from the approaches verify the occurrences of Rossby-gravity modes (m = 3 and 4 at periods T = 2.1 and 1.7 days), and their secondary waves (SWs) generated from interactions with diurnal, semi-diurnal, ter-diurnal, and quatra-diurnal migrating tides. We further extend the PDT to 2012–2019, illustrating that Q2DWs exhibit significant interannual variability. Composite analysis reveals seasonal and altitude variations of the Rossby-gravity modes and their SWs. The Rossby-gravity modes maximize in local summer, whereas their 16- and 9.6-h SWs appear more in winter.
- ItemQuasi‐2‐Day Wave in Low‐Latitude Atmospheric Winds as Viewed From the Ground and Space During January–March, 2020(Hoboken, NJ : Wiley, 2021) He, Maosheng; Chau, Jorge L.; Forbes, Jeffrey M.; Zhang, Xiaoli; Englert, Christoph R.; Harding, Brian J.; Immel, Thomas J.; Lima, Lourivaldo M.; Bhaskar Rao, S. Vijaya; Ratnam, M. Venkat; Li, Guozhu; Harlander, John M.; Marr, Kenneth D.; Makela, Jonathan J.Horizontal winds from four low-latitude (±15°) specular meteor radars (SMRs) and the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument on the ICON satellite, are combined to investigate quasi-2-day waves (Q2DWs) in early 2020. SMRs cover 80–100 km altitude whereas MIGHTI covers 95–300 km. Q2DWs are the largest dynamical feature of the summertime middle atmosphere. At the overlapping altitudes, comparisons between the derived Q2DWs exhibit excellent agreement. The SMR sensor array analyses show that the dominant zonal wavenumbers are s = +2 and + 3, and help resolve ambiguities in MIGHTI results. We present the first Q2DW depiction for s = +2 and s = +3 between 95 and 200 km, and show that their amplitudes are almost invariant between 80 and 100 km. Above 106 km, Q2DW amplitudes and phases present structures that might result from the superposition of Q2DWs and their aliased secondary waves.
- ItemSpring‐Fall Asymmetry in VLF Amplitudes Recorded in the North Atlantic Region: The Fall‐Effect(Hoboken, NJ : Wiley, 2021) Macotela, E.L.; Clilverd, M.; Renkwitz, T.; Chau, J.; Manninen, J.; Banyś, D.A spring-fall asymmetry is observed in daytime amplitude values of very low frequency (VLF) radio wave signals propagating over the North Atlantic during 2011–2019. We explore the processes behind this asymmetry by comparing against mesospheric mean temperatures and the semidiurnal solar tide (S2) in mesospheric winds. The solar radiation influence on VLF subionospheric propagation was removed from the daytime VLF amplitude values, isolating the fall-effect. Similarly, the symmetric background level was removed from mesospheric mean temperatures undertaking comparable analysis. During fall, all three analyzed parameters experience significant deviation from their background levels. The VLF amplitude variation during spring is explained by the seasonal variation in solar illumination conditions, while the fall-effect can be interpreted as a mean zonal wind reversal associated with both a S2 enhancement, and temperature reductions. Decreases in temperature can produce decreases in collision frequency, reducing VLF signal absorption, driving the observed VLF asymmetry.
- ItemCalifornian Wildfire Smoke Over Europe: A First Example of the Aerosol Observing Capabilities of Aeolus Compared to Ground‐Based Lidar(Hoboken, NJ : Wiley, 2021) Baars, Holger; Radenz, Martin; Floutsi, Athena Augusta; Engelmann, Ronny; Althausen, Dietrich; Heese, Birgit; Ansmann, Albert; Flament, Thomas; Dabas, Alain; Trapon, Dimitri; Reitebuch, Oliver; Bley, Sebastian; Wandinger, UllaIn September 2020, extremely strong wildfires in the western United States of America (i.e., mainly in California) produced large amounts of smoke, which was lifted into the free troposphere. These biomass-burning-aerosol (BBA) layers were transported from the US west coast toward central Europe within 3–4 days turning the sky milky and receiving high media attention. The present study characterizes this pronounced smoke plume above Leipzig, Germany, using a ground-based multiwavelength-Raman-polarization lidar and the aerosol/cloud product of ESA’s wind lidar mission Aeolus. An exceptional high smoke-AOT >0.4 was measured, yielding to a mean mass concentration of 8 μg m−3. The 355 nm lidar ratio was moderate at around 40–50 sr. The Aeolus-derived backscatter, extinction and lidar ratio profiles agree well with the observations of the ground-based lidar PollyXT considering the fact that Aeolus’ aerosol and cloud products are still preliminary and subject to ongoing algorithm improvements.
- ItemEarly Warning of the Pacific Decadal Oscillation Phase Transition Using Complex Network Analysis(Hoboken, NJ : Wiley, 2021) Lu, Zhenghui; Yuan, Naiming; Yang, Qing; Ma, Zhuguo; Kurths, JürgenObtaining an efficient prediction of the Pacific Decadal Oscillation (PDO) phase transition is a worldwide challenge. Here, we employed the climate network analysis to uncover early warning signals prior to a PDO phase transition. This way an examination of cooperative behavior in the PDO region revealed an enhanced signal that propagated from the western Pacific to the northwest coast of North America. The detection of this signal corresponds very well to the time when the upper ocean heat content in the off-equatorial northwestern tropical Pacific reaches a threshold, in which case a PDO phase transition may be expected with the arising of the next El Ni urn:x-wiley:00948276:media:grl61986:grl61986-math-0001o/La Niurn:x-wiley:00948276:media:grl61986:grl61986-math-0002 a event. The objectively detected early warning signal successfully forewarned all the six PDO phase transitions from the 1890–2000, and also underpinned the possible PDO phase transition around 2015, which may be triggered by the strong El Niurn:x-wiley:00948276:media:grl61986:grl61986-math-0003o event in 2015–2016.
- ItemDetermination of the Azimuthal Extent of Coherent E‐Region Scatter Using the ICEBEAR Linear Receiver Array(Hoboken, NJ : Wiley, 2021) Huyghebaert, Devin; McWilliams, Kathryn; Hussey, Glenn; Galeschuk, Draven; Chau, Jorge L.; Vierinen, JuhaThe Ionospheric Continuous-wave E-region Bistatic Experimental Auroral Radar (ICEBEAR) is a VHF coherent scatter radar that operates with a field-of-view centered on 58°N, 106°W and measures characteristics of ionospheric E-region plasma density irregularities. The initial operations of ICEBEAR utilized a wavelength-spaced linear receiving array to determine the angle of arrival of the ionospheric scatter at the receiver site. Initially only the shortest baselines were used to determine the angle of arrival of the scatter. This publication uses this linear antenna array configuration and expands on the initial angle of arrival determination by including all the cross-spectra available from the antenna array to determine both the azimuthal angle of arrival and the azimuthal extent of the incoming ionospheric scatter. This is accomplished by fitting Gaussian distributions to the complex coherence of the signal between different antennas and deriving the azimuthal angle and extent based on the best fit. Fourteen hours of data during an active ionospheric period (March 10, 2018, 0–14 UT) were analyzed to investigate the Gaussian fitting procedure and determine its feasibility for implementation with ICEBEAR. A comparison between mapped scatter, both neglecting azimuthal extent and including azimuthal extent is presented. It demonstrates that the azimuthal extent of the ionospheric E-region scatter is very important for accurately portraying and analyzing the ICEBEAR measurements.