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Why does the October Effect not occur at nighttime?

Wendt, Vivien and Schneider, Helen and Banyś (geb. Wenzel), Daniela and Hansen, Marc and Clilverd, Mark (2023) Why does the October Effect not occur at nighttime? IUGG 2023, 12.-19.Jul. 2023, Berlin, Deutschland.

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Abstract

Radar waves with very low frequency (VLF) are reflected at the lower edge of the ionosphere, in the D-region. The D-region (60 - 90km) is influenced by the solar zenith angle and space weather from above as well as by dynamical and chemical processes in the mesosphere. During October there is a well-known sharp decrease of the daytime VLF amplitude between transmitter and receiver combinations whose great circle paths lie mainly in polar latitudes. Until now we do not know what causes the October effect. Space weather phenomena can be ruled out as a cause since their time scales are either too short or too long. The solar zenith angle, strongly influencing the seasonal variation of the VLF amplitude can also be ruled out as a similar behavior is not observed in spring. Thus, there is a strong assumption that neutral dynamical processes in the mesosphere play a major role. We assume and confirm that a regional warming in the lower mesosphere, occurring simultaneously and with similar characteristics as the October effect, plays a major role in the formation process of the October effect. The VLF reflection height is about 15km higher during nighttime than during daytime. This difference in combination with the location of the regional warming explains, why the October effect can not be observed during nighttime.

Item URL in elib:https://elib.dlr.de/196217/
Document Type:Conference or Workshop Item (Poster)
Title:Why does the October Effect not occur at nighttime?
Authors:
AuthorsInstitution or Email of AuthorsAuthor's ORCID iDORCID Put Code
Wendt, VivienUNSPECIFIEDhttps://orcid.org/0000-0003-1806-4507UNSPECIFIED
Schneider, HelenUNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Banyś (geb. Wenzel), DanielaUNSPECIFIEDhttps://orcid.org/0000-0001-6623-6612UNSPECIFIED
Hansen, MarcUNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Clilverd, MarkBritish Antarctic Survey, High Cross, Cambridge, UKhttps://orcid.org/0000-0002-7388-1529UNSPECIFIED
Date:16 July 2023
Refereed publication:No
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Status:Published
Keywords:October effect, VLF observation, Atmosphere Dynamics
Event Title:IUGG 2023
Event Location:Berlin, Deutschland
Event Type:international Conference
Event Dates:12.-19.Jul. 2023
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Earth Observation
DLR - Research area:Raumfahrt
DLR - Program:R EO - Earth Observation
DLR - Research theme (Project):R - Middle Atmosphere
Location: Neustrelitz
Institutes and Institutions:Institute for Solar-Terrestrial Physics > Solar-Terrestrial Coupling Processes
Deposited By: Wendt, Dr. Vivien
Deposited On:22 Aug 2023 09:41
Last Modified:22 Aug 2023 09:41

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