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Abstract Overly smooth topography in general circulation models (GCMs) underestimates the blocking effect of the steep mountain ranges flanking the eastern Pacific. We explore the impact of this bias on common biases in Pacific climate simulation [i.e., the unrealistic cross-equatorial symmetry of near-surface winds, sea surface temperatures (SSTs), and precipitation] through sensitivity experiments with modified Central and/or South American topography in an atmosphere–ocean coupled GCM. Quantifying orographic blocking potential via the Froude number, we determine that an envelope topographic interpolation scheme best captures observed blocking patterns. Implementing envelope topography only in Central America reduced model biases as greater blocking of the trade winds warmed SST and enhanced convergence in the northeastern Pacific. Doing so additionally over the Andes improved the simulation of South Pacific circulation and the South Pacific convergence zone as stronger deflection of the westerlies intensified the South Pacific anticyclone. This mitigated convection biases in the southeast Pacific by increasing subsidence and cooling SST. However, remote impacts of the Andes exacerbated the dry bias in the northeast tropical Pacific, resulting in negligible improvement in the East Pacific double-ITCZ. We find that, due to the significant role of large-scale convergence in driving precipitation patterns, other model biases, such as cloud-radiative biases, may modulate the impact of altering topography. Our results highlight the importance of considering alternate methods for calculating model topographic boundary conditions, though the optimal interpolation scheme will vary with model resolution and the impact of topography on GCM biases can be sensitive to choices made in formulating parameterizations. Significance StatementIn this study, we explore how the mountain ranges spanning Central and South America shape the climate of the Pacific by blocking large-scale midlatitude and tropical winds. We show that the height of these mountains is typically too low in climate models and that elevating them can improve patterns of rainfall, surface ocean temperatures, and near-surface winds in the Pacific. This is important because model biases in the Pacific climate limit their utility for understanding current and future climate variability. Improving the representation of blocking by mountains can thus be a simple method for reducing uncertainties in future climate projections. 

Abstract The Eastern Pacific Warm Pool (EPWP) modulates global climate through its connection with tropical Pacific circulation, but sparse paleoceanographic data from this region limits our understanding of its role in past climate variability. We present a 144 kyr alkenone‐sea surface temperature (SST) reconstruction from core NH22P, located in the northern EPWP, that shows local warming occurred during periods of global cooling. Climate model simulations of the Last Glacial Maximum indicate that both ice sheet and greenhouse gas forcing slowed wind speeds over the EPWP, which attenuated glacial cooling of local SST via the wind‐evaporation‐SST feedback. Spectral analysis further suggests precessional pacing of the warming spikes. Vernal equinox insolation could explain this pacing as direct shortwave heating during boreal spring would have contributed to the early seasonal intensification of the EPWP. This work provides crucial constraints on tropical Pacific glacial climate variability and highlights the unique response of the EPWP to global climate forcings. 

Abstract We explore the response of northeastern Pacific sea surface temperature (SST) to deglacial (16–7 ka) climate variability as recorded in‐based SST reconstructions spanning 65°N to 10°S. Included in the analysis is a new 23 kyr SST record from core NH8P from the northwest Mexican Margin. We isolate spatiotemporal patterns in regional SSTs with trend empirical orthogonal function (TEOF) analysis. The dominant TEOF mode reflects deglacial warming associated with rising. Tropical and subtropical SSTs correlated most strongly with this mode, suggesting that the thermodynamic response of the tropical eastern Pacific to greenhouse gas forcing was the dominant driver of regional SST change during deglaciation. The second TEOF mode reflects millennial‐scale variability and is most strongly expressed in subpolar SSTs. The synchronous timing between North Pacific and North Atlantic SST oscillations is evidence for the rapid transmission of millennial‐scale climate perturbations between the basins, likely through an atmospheric teleconnection. SSTs at NH8P have no correlation with either leading TEOF mode as there is minimal change in SST at this site after20 ka. A model simulation of the LGM indicates that glacial cooling was muted in much of the Eastern Pacific Warm Pool (EPWP), in which NH8P lies, due to reductions in latent heat flux. This suggests that the wind‐evaporation‐SST feedback was responsible for the attenuation of EPWP cooling. Overall, this study highlights the distinct latitudinal trends in the Pacific's response to deglaciation.