Assessing environmental conditions associated with spatially varying rainfall structure of North Atlantic tropical cyclones: An object‐based climatological analysis

Abstract

This study utilizes geographic information system‐based shape analyses with spatial regressions to examine the spatial variations in the relationships between North Atlantic TC rain field patterns and the environmental conditions. We measure the area, solidity, dispersion and closure of rain fields associated with North Atlantic tropical cyclones (TCs) during 1998–2014 from satellite‐based rain rate estimates. The potential contributing factors examined include storm intensity, translational speed, sea surface temperature, total precipitable water, upper‐tropospheric divergence, deep‐layer vertical wind shear and distance to land. Spatial metrics of rainfall, TC attributes and environmental conditions are aggregated onto a hexagon grid, and the average values are used in regression models. Spatial autoregressive regression and geographically weighted regression are applied to investigate the relationships between contributing factors and rainfall patterns. Storm intensity is positively correlated with area, solidity and closure and negatively correlated with dispersion. Higher moisture and larger upper‐level divergence contribute to a larger rainfall field with a more dispersed and less solid pattern, especially over the western Gulf and the western Caribbean. Wind shear and storm motion affect rain field patterns differently depending on the juxtaposition and relative magnitude of storm motion and wind shear vectors and thus exhibit more regional variations. This research further highlights the importance of incorporating a spatial component into the research on TC rainfall climatology. An improved understanding of basin‐wide and sub‐basin‐wide relationships between TC rain fields and contributing factors would benefit rainfall forecasting and hazard mitigation.

Classification of tropical cyclone rain patterns using convolutional autoencoder

“…The environmental conditions were averaged within 800 km radius from the storm center. For the calculation of VWS, values within 200 km of each TC sample were not analyzed to exclude strong circulation of the TC 15 , 16 , 24 , 34 , 46 . As the R17 can represent the spatial scale of major vortex of a TC, we also performed the analyses using R17.…”

“…TC rain images were cropped from the IMERG precipitation data in a grid box of 96 × 96 pixels (approximately 1000 km × 1000 km size) along the TC center. Since the cropped image may contain rain fields not associated with the TC, only TC rain fields were extracted using the following method: 1) all rain polygons were searched in the cropped image where a rain polygon is defined as a set of one or more connected pixels with rain rates ≥ 1 mm h −1 , 2) rain polygons where the minimum distance between the edge of rain polygon and the TC center is > 500 km were removed 14 , 35 , 46 , 66 , 67 . This study focuses on major rain field of TC within 500 km radius including the eyewall and the rain band structures that spirals into the storm center 1 , 68 .…”

“…Previous studies have shown that regional variations exist in TC rain shape within the Atlantic Basin 35 , 46 . Thus, we examine the frequency with which each of our clusters occurs over the basin and find distinct variations in the geographical locations of their occurrences.…”

“…3 ). The five metrics include rainfall area (RA), asymmetries in north–south and east–west directions (ASYM_NS and ASYM_EW, respectively), dispersion (DISP), and degree of division (DIVD) (Data and methods) which have been commonly used to measure spatial characteristics of TC rain 33 , 35 , 46 , 47 . We calculate the five metrics for pixels with rain rates greater than 3 and 9 mm hr −1 to investigate patterns of moderate- and heavy-rain in TCs, respectively.…”

Leading role of Saharan dust on tropical cyclone rainfall in the Atlantic Basin

“…In addition, recent satellite observations revealed a decreasing trend of rain rate in the core part of TCs but increasing trend in outer bands (7,8). Besides ocean surface temperature and water vapor in the atmosphere, other environmental factors regulate the regional variations of TCR, including vertical wind shear (9)(10)(11), surface roughness change (12)(13)(14), and atmospheric aerosols (15,16). How the environment and climate influence the TCR remains unresolved, especially over multiyear to decadal time scales.…”