Winter sea-level response asymmetry remained uncertain for San Diego minus Fremantle in 1951-2024

We tested equal warm and cold ENSO slopes in December-February San Diego minus Fremantle sea level. A fixed PSMSL snapshot and NOAA CPC ERSSTv5 index gave 62 complete winters within 1951-2024. A fit with a linear time trend gave warm and cold slopes of 70.46 and 111.85 mm per degree C. The warm minus cold slope was -41.39 mm per degree C. Its conditional 95% five-year wild block interval was -90.05 to 7.65. The primary result leaves asymmetry uncertain. A stricter missing-day check also included zero. Removing winters 1983, 1998, and 2016 gave an interval below zero, so the conclusion depends on support and quality rules. This is a test of association, not a physical cause or forecast. Two gauges, missing winters, one index baseline, and approximate uncertainty limit inference. The package contains source members, hashes, code, all winter values, uncertainty draws, a figure, and numerical checks.

sea level · ENSO · San Diego · Fremantle · response asymmetry · null result