ROTATE: A Coordinate System for Analyzing Atmospheric Rivers

This study introduces the ROTated Atmospheric river coordinaTE (ROTATE) system — a novel storm‐centric coordinate system designed specifically for analyzing atmospheric rivers (ARs). It effectively preserves key AR signals in the time mean that may be lost or obscured in simple averaging due to diverse AR orientations and shapes. By applying the ROTATE system, we compared climatological characteristics for northern hemisphere ARs. Composites of four key meteorological variables, integrated vapor transport, integrated water vapor, precipitation, and windspeed, indicate distinct and clearer patterns of ARs compared to the conventional non‐rotated AR centroid‐based compositing approach. Moreover, the ROTATE system improves precipitation rates, particularly around the AR center and its head and tail regions, providing more distinct delineations of the precipitation signals between landfalling and oceanic ARs. Overall, the ROTATE system has the potential to serve as a valuable tool for better comparing and understanding the characteristics, processes, and impacts of ARs across different regions. Plain Language Summary This study introduces a new method called ROTATE, designed to study long, narrow filamentary regions of intense water vapor transport in the lower atmosphere or so‐called atmospheric rivers (ARs). ROTATE helps us retain essential details in weather systems when averaging over time that otherwise might get lost using the usual averaging method. We used ROTATE to look at crucial characteristics of ARs such as how wet the air is, how fast the wind blows, how much water vapor is being transported, and how much rain falls. We found more apparent AR patterns with ROTATE compared to the traditional way of averaging ARs. The new method also helps us see finer details in rain distributions over land versus over the oceans. The results indicate ROTATE is a valuable tool to help us better compare and understand mean characteristics of ARs in different places. Key Points Introduces a new coordinate system for analyzing atmospheric rivers (ARs) Provides clearer AR composite patterns and their multi‐variate relationships when compared to the conventional non‐rotated AR centroid Enhances the distinction of precipitation signals between landfall and oceanic ARs, especially around the AR center and its head/tail