2024 Workshop: What is a Patch?
Gareth Perry
Lindsay Goodwin
Shasha Zou
Toshi Nishimura
Angeline Burrell
Asti Bhatt
Katrina Bossert
Matt Zettergren
Alanah Cardenas-O’Toole
Polar cap patches (or just “patches”) have been ubiquitous in discussions of dynamics and structuring in the polar cap for decades. These have traditionally been defined as F-region plasma density enhancements that are at least double the background density, often with the assumption that these are structures on scales of ~100 km. Recently, there has been a significant amount of debate over whether this traditional definition is accurate, or even if it is appropriate to consider all “patches” one single phenomena. There are a number of processes that could cause localized plasma density enhancements, including but not limited to soft precipitation, waves like Traveling Ionospheric Disturbances (TIDs), and Tongues of Ionization (TOIs). It is possible that many of these “other” phenomena have been routinely misidentified as patches in the polar cap. There is further debate about the extent to which observational biases (i.e., under-resolving or limited viewing geometries) impact how we describe patches. These plasma structures are important as they are known to be connected to a variety of physical processes, such as trailing-edge gradient drift instability that drives small-scale structuring or off-great-circle HF propagation.
This session welcomes open discussion of the questions “What is a patch?” from a variety of modeling, theory, and observational perspectives. This includes both debate over the technical definition of patches, as well as details about their generation mechanisms and properties, as it is likely these will be integral to describing the phenomena. The session will consist of several talks to give background on the issue and an extended discussion period. We welcome submitted presentations with specific results that contribute to the discussion of what is (or is not) a patch in the polar cap, but encourage authors to reach out to conveners early with their topics as there will be a concerted effort to keep the session focused. Students and early-career researchers are highly encouraged to participate in this session as changing consensus will impact how the polar cap is viewed and studied in the future.
Descriptions of polar cap patches have percolated high-latitude literature for 75 years. However there has recently been debate over whether the terminology, or even the idea of patches as an unique and unambiguous phenomena, is appropriate. Effectively, it is unclear the extent to which the term “patch” has been used to describe potentially unrelated phenomena (convoluting processes that occur within, above, and below the ionosphere), or traditionally discrete phenomena. For instance, an argument could be made that many plasma structures that would typically be described as patches could be more similar to wave-like structures, such as TIDs. Similarly, there is debate as to the extent that patches and TOIs are actually independent phenomena vs the same thing observed with different techniques or at different stages in its life cycle. This session aims to bring together experts not only in polar cap structuring, but also waves and other high-latitude phenomena to see evidence of similarities and differences in different identified structuring in the polar cap and come to some consensus about whether or not present categorization makes physical sense, or if it should be reconsidered.