Observations of polar mesospheric summer echoes resembling kilometer-scale varicose-mode flows
The mesosphere and lower thermosphere (MLT) region represents a captivating yet challenging field of research. Remote sensing techniques, such as radar, have proven invaluable for investigating this domain. The Middle Atmosphere Alomar Radar System (MAARSY), located in northern Norway (69 ∘ N, 16 ∘...
| Published in: | Annales Geophysicae |
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| Main Authors: | , , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Copernicus Publications
2024
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| Subjects: | |
| Online Access: | https://doi.org/10.5194/angeo-42-29-2024 https://doaj.org/article/b173710ab09241be9c21638166236600 |
| Summary: | The mesosphere and lower thermosphere (MLT) region represents a captivating yet challenging field of research. Remote sensing techniques, such as radar, have proven invaluable for investigating this domain. The Middle Atmosphere Alomar Radar System (MAARSY), located in northern Norway (69 ∘ N, 16 ∘ E), uses polar mesospheric summer echoes (PMSEs) as tracers to study MLT dynamics across multiple scales. Chau et al. ( 2021 ) recently discovered a spatiotemporally highly localized event showing a varicose mode (simultaneous upward and downward movements), which is characterized by extreme vertical velocities ( | w | ≥ 3 σ <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="40pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="19a3c5d15fd5057a0ad7c4c6aae5b224"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="angeo-42-29-2024-ie00001.svg" width="40pt" height="13pt" src="angeo-42-29-2024-ie00001.png"/></svg:svg> ) of up to 60 m s −1 in the vertical drafts. Motivated by this finding, our objective is to identify and quantify similar extreme events or comparable varicose structures, i.e., defined by quasi-simultaneous updrafts and downdrafts, that may have been previously overlooked or filtered out. To achieve this, we conducted a thorough manual search through a MAARSY dataset, considering the PMSE months (i.e., May, June, July, August) spanning from 2015 to 2021. This search has revealed that these structures do indeed occur relatively frequently with an occurrence rate of up to 2.5 % per month. Over the 7-year period, we observed and recorded more than 700 varicose-mode events with a total duration of about 265 h and documented their vertical extent, vertical velocity characteristics, duration, and their occurrence behavior. Remarkably, these events manifest throughout the entire PMSE season with pronounced occurrence rates in June and July, while the probability of their occurrence decreases towards the beginning and end of the PMSE seasons. Furthermore, their ... |
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