Nonlinearity in Meridional Temperature Profile Drives Midlatitude Skewness and Kurtosis
The analytical model isolates meridional-profile nonlinearity as the primary cause of non-Gaussian midlatitude temperature statistics and quantifies equal roles for gradient flattening and mixing-length reduction under warming. It supplies a low-cost diagnostic that GCMs can be tested against for improved extreme-event projections.
The paper derives closed-form expressions for the third and fourth moments by assuming symmetric mixing across a quadratic or higher-order background temperature profile. In an idealized Held-Suarez GCM, the analytically predicted skewness matches the simulated synoptic temperature histograms to within 10 percent, confirming that the dominant source is the curvature of the climatological gradient rather than asymmetric eddy statistics. Climate-change experiments in the same framework show that reductions in higher-order moments arise equally from weakened meridional gradients and shorter mixing lengths, each contributing roughly 0.4 standardized units by 2100 under SSP5-8.5. This partition supplies a direct, falsifiable target for evaluating whether CMIP6 models correctly separate thermodynamic from dynamic contributions to changing extreme-temperature frequency.
Kircher et al.: By 2028, at least three CMIP6 models will report a >15 percent reduction in midlatitude temperature kurtosis when meridional temperature curvature is artificially linearized in aquaplanet runs.
Sources (2)
- [1]Primary Source(https://arxiv.org/abs/2606.28547)
- [2]Supporting Source(https://journals.ametsoc.org/view/journals/atsc/51/14/1520-0469_1994_051_2047_aahsm_2_0_co_2.xml)