A suite of general circulation models is used to investigate the surface magnetic perturbations due to the ionospheric currents driven by an eastward‐propagating ultrafast Kelvin wave (UFKW) packet with periods between 2 and 4 days and zonal wave number
Numerical experiments are performed using a suite of general circulation models that enable the interaction between a Kelvin wave packet and the ionosphere‐thermosphere (IT) to be elucidated. Focus is on an eastward‐propagating ultra‐fast Kelvin wave (UFKW) packet with periods between 2 and 4 days and zonal wavenumber
- NSF-PAR ID:
- 10375342
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 125
- Issue:
- 5
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract . The simulated daytime UFKW‐driven meridional magnetic perturbations dBn ( ∼± 5 nT) (or zonal currents) between about 5° and 20° magnetic latitude in each hemisphere are opposite in sign to those equatorward of± 5° and produced by the equatorial electrojet (EEJ), with the directions on any given day determined by the phase of the UFKW as it propagates eastward with respect to the sunlit ionosphere. Since the nominal daytime zonal current betweenS q ∼± 30° is uniformly eastward flowing, the present results are consistent with the hypothesis that the EEJ is part of a local current vortex with oppositely directed currents near the equator versus those between 5° and 20° at low latitudes. UFKWs are a special wave type wherein meridional winds are relatively small, which leads to our finding that the EEJ dBn constitutes a simple quantitative proxy forE ‐region UFKW neutral winds near the 107‐km peak height of the Hall conductivity, including the variable wave period of the UFKW packet. Numerical experiments are also performed to understand the longitude distribution of actual ground magnetometer measurements that are needed to reliably extract the UFKW dBn signal and hence the neutral winds, both of which are closely linked to plasma drifts and electron densities in the equatorialF region. Using actual magnetometer data it is moreover shown that the UFKW dBn signal is easily measurable. Therefore measurements of EEJ dBn can potentially be used to infer UFKW activity for scientific investigations focusing on coupling between the tropical troposphere and the ionosphere‐thermosphere. -
Abstract This work shows a 3-year climatology of the horizontal components of the solar diurnal tide, obtained from wind measurements made by a multistatic specular meteor radar (SIMONe) located in Jicamarca, Peru (12
S, 77$$^\circ$$ W). Our observations show that the meridional component is more intense than the zonal component, and that it exhibits its maxima shifted with respect to the equinox times (i.e., the largest peak occurs in August–September, and the second one in April–May). The zonal component only shows a clear maximum in August–September. This observational climatology is compared to a climatology obtained with the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X). Average comparisons indicate that the model amplitudes are 50% smaller than the observed ones. The WACCM-X results are also used in combination with observed altitude profiles of the tidal phases to understand the relative contributions of migrating and non-migrating components. Based on this, we infer that the migrating diurnal tide (DW1) dominates in general, but that from June until September (November until July) the DE3 (DW2) may have a significant contribution to the zonal (meridional) component. Finally, applying wavelet analysis to the complex amplitude of the total diurnal tide, modulating periods between 5 and 80 days are observed in the SIMONe measurements and the WACCM-X model. These modulations might be associated to planetary waves and intraseasonal oscillations in the lower tropical atmosphere.$$^\circ$$ Graphical Abstract -
Abstract “Ultra‐fast” Kelvin waves (UFKWs) serve as a mechanism for coupling the tropical troposphere with the mesosphere, thermosphere and ionosphere. Herein, solutions to the linearized wave equations in a dissipative thermosphere in the form of “Hough Mode Extensions (HMEs)” are employed to better understand the vertical propagation of the subset of these waves that most effectively penetrate into the thermosphere above about 100 km altitude; namely, UFKWs with periods ≲4 days, vertical wavelengths (
λ z ) ≳30 km, and zonal wavenumbers = −1. Molecular dissipation is found to broaden latitude structures of UFKWs with increasing height while their vertical wavelengths (λ z ) increase with latitude. Collisions with ions fixed to Earth's magnetic field (“ion drag”) are found to dampen UFKW amplitudes, increasingly so as the densities of those ions increase with increased solar flux. The direct effect of ion drag is to decelerate the zonal wind. This leads to suppression of vertical velocity and the velocity divergence, and related terms in the continuity and thermal energy equations, respectively, that lead to diminished perturbation temperature and density responses. Access is provided to the UFKW HMEs analyzed here in tabular and graphical form, and potential uses for future scientific studies are noted. -
Abstract The boreal‐winter stratospheric polar vortex is more disturbed when the quasi‐biennial oscillation (QBO) in the lower stratosphere is in its easterly phase (eQBO), and more stable during the westerly phase (wQBO). This so‐called “Holton–Tan effect” (HTE) is known to involve Rossby waves (RWs) but the details remain obscure. This tropical–extratropical connection is re‐examined in an attempt to explain its intraseasonal variation and its relation to Rossby wave breaking (RWB). Reanalyses in isentropic coordinates from the National Centers for Environmental Prediction Climate Forecast System for the 1979–2017 period are used to evaluate the relevant features of RWB in the context of waveguide, wave–mean‐flow interaction, and the QBO‐induced meridional circulation. During eQBO, the net extratropical wave forcing is enhanced in early winter with ∼25% increase in upward propagating planetary‐scale Rossby waves (PRWs) of zonal wave‐number 1 (wave‐1). RWB is also enhanced in the lower stratosphere, characterized by convergent anomalies in the subtropics and at high latitudes and strengthened waveguide in between at 20°N–40°N, 350–650 K. In late winter, RWB leads to finite amplitude growth, which hinders upward propagating PRWs. The effect is most significant for zonal wave‐numbers 2 and 3 (wave‐2‐3). During wQBO, RWB in association with wave‐2‐3 is enhanced in the upper stratosphere. Wave absorption/mixing in the surf zone reinforces a stable polar vortex in early to middle winter. A poleward confinement of the extratropical waveguide in the upper stratosphere forces RWB to extend downward around January. A strengthening of upward propagating wave‐2‐3 follows and the polar‐vortex response switches from reinforcement to disturbance around February, thus a sign reversal of the HTE in late winter.
Key Findings • Rossby wave breaking (RWB) is enhanced in the height regions where the zero‐wind line is shifted into the winter hemisphere and where the QBO‐induced meridional circulation is directed toward the winter pole
• Polar vortex responses differ in terms of the height location of RWB, zonal wave‐number‐dependent disturbances and seasonal development
• Significant increase in wave‐1 occurs when the QBO is in its easterly phase
• A cumulative effect of RWB results in enhanced wave forcing of zonal wave‐numbers 2 and 3 during westerly QBO, which manifests in a sign reversal of the Holton–Tan effect in late winter.
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