Reply to Comment on Moist Static Energy Transport Trends in Four Global Reanalyses: Are They Downgradient? by Clark et al. (2022)

In a previous study, we investigated whether reanalysis moist static energy (MSE) transport trends over the 1980 through 2018 period are consistent (a) with each other and (b) with the finding that these transport trends are downgradient, as found in climate models. Regarding point (a), our conclusion was that MSE transport trends were dependent on the reanalysis data set. However, Cox et al. (2023) correctly point out that the reanalysis dependence is reduced dramatically if a barotropic mass flux correction is applied at a monthly mean timescale prior to computing the MSE transport trends. In our reply below, we revisit point (b) after applying this correction. We find that even after the correction, reanalysis MSE transport trends are not downgradient nor poleward in the Northern Hemisphere extratropics. However, reanalysis does show a compensation between dry static and latent energy transport trends, which has been shown in climate models historically. Plain Language Summary Energy is transported poleward by the atmospheric circulation. As the climate warms, the amount of energy transported poleward is projected to increase. In a previous study, we investigated whether this holds in reanalysis data sets (data sets that obtain global coverage by combining measurements with numerical models). However, as pointed out by Cox et al. (2023), we did not account for the fact that reanalysis products do not respect mass conservation. Correcting for this, MSE transport trends do not exhibit a reanalysis dependence to the degree we previously found. Nevertheless, reanalysis MSE transports are not associated with changes in the surface MSE gradient, as models suggest, nor are these fluxes poleward in the Northern Hemisphere extratropics. An aspect that becomes more consistent between models and reanalysis after correcting the mass budget is an anticorrelation between dry static and latent energy transports trends.

Automated summary

This study examines whether the reanalysis moist static energy (MSE) transport trends are consistent with the downgradient transport trends found in climate models. It is found that the MSE transport trends depend on the reanalysis dataset, but this dependence is reduced when a barotropic mass flux correction is applied. However, even after the correction, the reanalysis MSE transport trends are not consistent with the models' predictions.