2024 Workshop: What is a Patch?

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.