Attribution of uncertainties in predictions of monsoon precipitation using an energy framework

Abstract

<p>Recent studies on monsoon dynamics have emphasized that monsoon changes are due to local anomalous Net Energy Input (NEI) in the atmospheric column, rather than being associated with land-sea temperature contrasts as in the classical large-scale sea-breeze view of monsoons. In the energy framework, a positive NEI (convergence of energy) must be balanced by a lateral export of moist static energy, which, if achieved by an overturning cell, is associated with moisture import and net precipitation.</p><p>This suggests a strong link between monsoonal precipitations and NEI, providing a pathway to understand uncertainties in predictions of past and future monsoon precipitation.</p><p>To investigate this, we exploit the CMIP5 and PMIP3 archives (9 models), comparing simulations of Mid-Holocene (~6000 years ago) and future (end of 21<sup>st</sup> century, RCP8.5 scenario) climates to pre-industrial (PI) control climate.</p><p>Precipitation responses to past and future forcing in monsoon regions exhibit a wide spread which is, as expected, significantly (and positively) correlated with NEI changes. Yet, the latter explain at best 40% of the spread in the precipitation response. In fact, the correlation between NEI and precipitation changes hides a more complex picture.</p><p>We show that changes in atmospheric stratification and differences in the control climate contribute to the uncertainties, with varying degrees depending on regions and climates: while the southern hemisphere monsoons are linked to changes in both stratification and NEI, the northern hemisphere monsoons are more strongly associated with stratification changes. Meanwhile, changes in the mid-Holocene are more dominated by NEI changes than in the future climate when stratification changes are larger.</p>