Mechanisms rectifying the annual mean response of tropical Atlantic rainfall to precessional forcing

Abstract

precipitation changes are largest in boreal summer, thus skewing the annual mean response. These results show that it is important to take into account the seasonality of climatic forcings, even when studying annual mean climate change.

A Conceptual Model for the Response of Tropical Rainfall to Orbital Variations

“…The discrepancies for the past 60 ka cannot be resolved by manipulating the model parameters, which points to effects not captured by our model, such as the zonal variations shown to be important in GCM simulations (Tigchelaar and Timmermann 2016). The model agrees reasonably well with the record from Papua New Guinea, capturing many of the variations over the past 350 ka, although apparently with some phase lags, pointing to factors not considered in our modeling approach.…”

“…At the same time, in the annual mean, the location of maximum precipitation shifts from the Southern to the Northern Hemisphere due to the nonlinear dependence of the model precipitation on local insolation. (Tigchelaar and Timmermann 2016). The zonal inhomogeneities lead to cancellations in the zonal average; hence, the pattern does not appear in the average.…”

“…Because our model cannot capture zonal variations in precipitation, it should be regarded as a zeroth-order approximation to regions such as the Australo-Asian monsoon sector. For example, in simulations with comprehensive climate models (Clement et al 2004;Tigchelaar and Timmermann 2016), annual-and zonalmean precipitation changes do not generally have a double dipole pattern because of zonal inhomogeneities in the precipitation field. Instead, the double dipole is present locally, for example, over Asia and Australia 21 .…”

“…Previous modeling studies have focused on general circulation model (GCM) simulations that either compare two different climate scenarios (e.g., high vs low obliquity or June vs December perihelion) or use accelerated orbital variations to study the seasonality of tropical precipitation (e.g., Kutzbach 1981;Kutzbach and Guetter 1986;Joussaume et al 1999;Clement et al 2004;Kutzbach et al 2008;Khon et al 2010;Pausata et al 2011;Merlis et al 2013;Tigchelaar and Timmermann 2016). The main benefit of these models lies in the fact that they can incorporate realistic continental boundary conditions and clouds, among other things.…”

Contrasting responses to orbital precession on Titan and Earth

“…But simulations with a Titan general circulation model (GCM) show that even without asymmetries in surface boundary conditions and consistent with the observed preferential hydrocarbon accumulation in the north, more annual‐mean net precipitation occurs in the northern hemisphere, preferentially in the north polar region in summer—apparently because the northern summer, albeit dimmer, is currently longer [ Schneider et al , ; Lora et al , ]. By contrast, enhanced annual‐mean net precipitation in Earth simulations occurs in the hemisphere with the brighter summer [ Kutzbach and Guetter , ], possibly because of correlations between insolation variations and the seasonal cycle of moisture advection [ Merlis et al , ] and/or because of nonlinear dynamical effects of continents on the mean circulation [ Tigchelaar and Timmermann , ].…”