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Creators/Authors contains: "Forbes, J. M."

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  1. Abstract

    A new Cloud Imaging and Particle Size (CIPS) gravity wave (GW) variance data set is available that facilitates automated analysis of GWs entering the mesosphere. This work examines several years of CIPS GW variances from 50 to 55 km in the context of the Arctic and Antarctic polar vortices. CIPS observes highest GW activity in the vortex edge region where horizontal wind speeds are largest, consistent with previously published GW climatologies in the stratosphere and mesosphere. CIPS observes the well‐documented planetary wave (PW)‐1 patterns in GW activity in both hemispheres. In the Northern Hemisphere, maximum GW activity occurs over the North Atlantic and western Europe. In the Southern Hemisphere, maximum GW activity stretches from the Andes over the South Atlantic and Indian Oceans, as expected. In the NH, CIPS GW spatial patterns are highly correlated with horizontal wind speed. In the SH, CIPS GW patterns are less positively correlated with the winds due to increased zonal symmetry and orographic forcing. The Andes Mountains and Antarctic Peninsula, South Georgia Island, Kerguelen/Heard Islands, New Zealand, and Tasmania are persistent sources of orographic GWs. Atmospheric Infrared sounder observations of stratospheric GWs are analyzed alongside CIPS to explore vertical GW coherence and to infer GW propagation and sources. NH midlatitude GW activity is reduced during the January 2021 SSW, as expected. This reduction in GWs leads to a simultaneous reduction in traveling ionospheric disturbances (TIDs), providing more evidence that weak polar vortex events with weak GW activity leads to reduced daytime TID activity.

     
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  2. Abstract

    Midlatitude thermospheric wind observations from the Michelson Interferometer for Global High‐resolution Thermospheric Imaging on board the Ionospheric Connections Explorer (ICON/MIGHTI) and from the ground‐based Boulder, Urbana, Millstone Hill and Morocco Fabry‐Perot interferometers (FPIs) are used to study a distinct solar local time (SLT) evolution in the nighttime wind field around the December solstice period. Our results show, to the best of our knowledge for the first time, strong non‐migrating tides in midlatitude thermospheric winds using coincident from different observing platforms. These observations exhibited a structure of strong (∼50–150 m/s) eastward and southward winds in the pre‐midnight sector (20:00–23:00 SLT) and in the post‐midnight sector (02:00–03:00 SLT), with a strong suppression around midnight. Tidal analysis of ICON/MIGHTI data revealed that the signature before midnight was driven by diurnal (D0, DE1, DE2, DW2) and semidiurnal (SE2, SE3, SW1, SW4) tides, and that strong terdiurnal (TE2, TW1, TW2, TW5) and quatradiurnal (QW2, QW3, QW6) tides were important contributors in the mid‐ and post‐midnight sectors. ICON/MIGHTI tidal reconstructions successfully reproduced the salient structures observed by the FPI and showed a longitudinal dual‐peak variation with peak magnitudes around 200°–120°W and 30°W–60°E. The signature of the structure extended along the south‐to‐north direction from lower latitudes, migrated to earlier local times with increasing latitude, and strengthened above 30°N. Tidal analysis using historical FPI data revealed that these structures were often seen during previous December solstices, and that they are much stronger for lower solar flux conditions, consistent with an upward‐propagating tidal origin.

     
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  3. Abstract

    An unusual sudden stratospheric warming (SSW) event occurred in the Southern Hemisphere in September 2019. Ground‐based and satellite observations show the presence of transient eastward‐ and westward‐propagating quasi‐10 day planetary waves (Q10DWs) during the SSW. The planetary wave activity maximizes in the mesosphere and lower thermosphere region approximately 10 days after the SSW onset. Analysis indicates that the westward‐propagating Q10DW with zonal wave numbers = 1 is mainly symmetric about the equator, which is contrary to theory which predicts the presence of an antisymmetric normal mode for such planetary wave. Observations from microwave limb sounder and sounding of the atmosphere using broadband emission radiometry are combined with meteor radar wind measurements from Antarctica, providing a comprehensive view of Q10DW wave activity in the Southern Hemisphere during this SSW. Analysis suggests that the Q10DWs of various wavenumbers are potentially excited from nonlinear wave‐wave interactions that also involve stationary planetary waves withs = 1 ands = 2. The Q10DWs are also found to couple the ionosphere with the neutral atmosphere. The timing of the quasi‐10‐day oscillations (Q10DOs) in the ionosphere are contemporaneous with the Q10DWs in the neutral atmosphere during a period of relatively low solar and geomagnetic activity, suggesting that the Q10DWs play a key role in driving the ionospheric Q10DOs during the Southern SSW event. This study provides observational evidence for coupling between the neutral atmosphere and ionosphere through the upward propagation of global scale planetary waves.

     
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