Large-scale climate response to regionally confined extratropical cooling: effect of ocean dynamics

This study investigates the effect of ocean dynamics on the tropical climate response to localized radiative cooling over three northern extratropical land regions using hierarchical model simulations that vary in the degree of ocean coupling. Without ocean dynamics, the tropical climate response is independent of the extratropical forcing location, characterized by a southward tropical precipitation shift with a high degree of zonal symmetry, a reduced zonal sea surface temperature gradient along the equatorial Pacific, and the eastward-shifted Walker circulation. When ocean dynamical adjustments are allowed, the zonal-mean tropical precipitation shift is damped primarily via Eulerian-mean ocean heat transport. The oceanic damping effect is strongest (weakest) for North Asian (American) cooling, associated with the largest (smallest) Eulerian-mean ocean heat transport across the equatorial Pacific. The cross-equatorial ocean heat transport in the Pacific is anchored to the North Pacific subtropical high, the response of which can be inferred from the corresponding slab ocean simulations. Hence, the slab ocean simulations provide useful a priori prediction for oceanic damping efficiency. Ocean dynamics also modulates the spatial pattern of climate response in a distinct manner depending on the zonal distribution of imposed forcing. North Asian forcing induces a pronounced eastern equatorial Pacific cooling extending to the western basin, accompanying the westward shifted Walker circulation. European forcing causes cooling confined to the eastern equatorial Pacific and strengthens the Walker circulation. The tropical precipitation response in these two cases exhibits large zonal variations with a high degree of equatorial symmetry, being essentially uncorrelated with the corresponding slab ocean simulations. By contrast, North American forcing induces a sufficiently strong inter-hemispheric contrast in the tropical Pacific SST response, due to the relatively weak oceanic damping effect, producing a weaker but spatially similar tropical response to that in the slab ocean simulation. This study demonstrates that the effect of ocean dynamics in modulating the tropical climate response depends on the extratropical forcing location. The results are relevant for understanding the distinct climate response induced by aerosols from different continental sites

Walker circulation response to extratropical radiative forcing

Walker circulation variability and associated zonal shifts in the heating of the tropical atmosphere have far-reaching global impacts well into high latitudes. Yet the reversed high latitude-to-Walker circulation teleconnection is not fully understood. Here, we reveal the dynamical pathways of this teleconnection across different components of the climate system using a hierarchy of climate model simulations. In the fully coupled system with ocean circulation adjustments, the Walker circulation strengthens in response to extratropical radiative cooling of either hemisphere, associated with the upwelling of colder subsurface water in the eastern equatorial Pacific. By contrast, in the absence of ocean circulation adjustments, the Walker circulation response is sensitive to the forcing hemisphere, due to the blocking effect of the northward-displaced climatological intertropical convergence zone and shortwave cloud radiative effects. Our study implies that energy biases in the extratropics can cause pronounced changes of tropical climate patterns

Observed and simulated air-sea feedbacks associated with enso and monsoon

Ph.D. University of Hawaii at Manoa 2011.Includes bibliographical references.Associated with the double ITCZ (Inter-tropical convergence zone) problem, a dipole SST bias pattern (cold in the equatorial central Pacific and warm in the southeast tropical Pacific) remains a common problem in current coupled models. Based on a newly-developed model, we demonstrated that a serious consequence of this SST bias is to suppress the thermocline feedback in El Niño/Southern Oscillation (ENSO) simulation. Firstly, the excessive cold tongue extension pushes the anomalous convection far westward, diminishing the convection-low level wind feedback and thus the air-sea coupling strength. Secondly, the equatorial surface wind anomaly exhibits weak meridional gradient, leading to a weakened wind-thermocline feedback. Thirdly, the equatorial cold SST bias induces a weakened upper-ocean stratification, yielding the underestimation of the thermocline-subsurface temperature feedback. Finally, the dipole SST bias underestimates the mean upwelling through both dynamic and thermodynamic effects. In recent decades, El Niño events have occurred more frequently over the equatorial central Pacific (CP Warming, CPW). Here, we ascribe this predominance of the CPW to a dramatic decadal change in the Pacific mean state and annual cycle. The mean state change characterized by a decadal La Niña-like pattern tends to anchor convection and surface zonal wind anomalies to the vicinity of the dateline, facilitating surface warming to occur in the CP. The annual cycle change, with the trade winds intensifying during boreal winter and spring, prevents the warming development but helps the warming decay in the EP. More CPW events are expected in the coming decade if the La-Niña-like pattern persists. The western North Pacific (WNP) Subtropical High (SH) has profound impacts on Asian summer monsoon, North Pacific storms. The cause of the interannual variability of WNPSH, however, remains controversial. Here we show that the anomalous WNPSH is primarily determined by a remote cooling/warming in the equatorial central Pacific and a positive thermodynamic feedback between the local circulation and a dipole sea surface temperature in the Indo-Pacific warm pool. We demonstrate that a physical-empirical prediction model built on these physical understandings has comparable performance with those of three state-of-the-art coupled climate models in re-forecast of the strength of the WNPSH

Hydrological character and sea-current structure in the front of Amery Ice Shelf

Hydrological character and Sea-current profiles structure are studied and analyzed in sea-area of the front of Amery Ice Shelf, Prydz Bay with LADCP, CTD data. These LADCP, CTD data were acquired during the 19th Chinese Antarctic Scientific Expedition. Results of this study agree with that, there exist four different kinds of water masses in the area of the front of Amery Ice Shelf in the summer of Antarctica. Current distribution presents a semi-circumfluence which flows in at the east and flows out in the west. Moreover, clockwise and anti-clockwise vortices were found in upper layer and mid-layer in the Prydz Bay. Western areas of these anti-clockwise vortices are positions of inflows from Prydz Bay to Amery Ice Shelf. The source of these inflows is the coastal westward current originated in the east of Prydz Bay. All these characteristics come down to the pattern of circumfluence, ice melt rate under Ice Shelf, scale of Ice Shelf water production and form of water exchanges between area of Ice Shelf and area of Prydz Bay

The effect of aging on the dynamics of reactive and proactive cognitive control of response interference

A prime-target interference task was used to investigate the effects of cognitive aging on reactive and proactive control in which frequency confounds and feature repetitions were eliminated from the cognitive control measures. We used distributional analyses to explore the dynamics of the two control functions by distinguishing the strength of incorrect response capture and the efficiency of suppression control. For reactive control, within-trial conflict control and between-trial conflict adaption were analyzed. The statistical analysis showed that there were no reliable between-trial conflict adaption effects for both young and older adults. For within-trial conflict control, the results revealed that older adults showed larger interference effects on mean RT and mean accuracy. Distributional analyses showed that the decline mainly stemmed from inefficient suppression rather than from stronger incorrect responses. For proactive control, older adults showed comparable proactive conflict resolution than young adults on mean RT and mean accuracy. Distributional analyses showed older adults were as effective as younger adults in adjusting their responses to minimize automatic response capture and actively suppress the direct response activation based on congruency proportion information. The results suggest that older adults were less proficient at suppressing interference after conflict was detected but can anticipate and prevent inference in response to congruency proportion manipulation. The results challenge earlier views that older adults have selective deficits in proactive control but are spared in reactive control

Disentangling the effect of regional SST bias on the double-ITCZ problem

This study investigates the causes of the double intertropical convergence zone (ITCZ) bias by disentangling the individual contribution of regional sea surface temperature (SST) biases. We show that a previously suggested Southern Ocean warm bias effect in displacing the zonal-mean ITCZ southward is diminished by the southern midlatitude cold bias effect. The northern extratropical cold bias turns out to be most responsible for a southward-displaced zonal-mean precipitation, but the zonal-mean diagnostics poorly represent the spatial pattern of the tropical Pacific response. Examination of longitude-latitude structure indicates that the overall spatial pattern of tropical precipitation bias is largely shaped by the local SST bias. The southeastern tropical Pacific wet bias is driven by warm bias along the west coast of South America with negligible influence from the Southern Ocean warm bias. While our model experiments are idealized with ocean dynamics being absent, the results shed light on where preferential foci should be applied in model development to improve the certain features of tropical precipitation bias

Features and spatial distribution of circumpolar deep water in the southern Indian Ocean and the effects of Antarctic circumpolar current

The data from the Southern Ocean observations of World Ocean Circulation Experiment (WOCE) are used for analysis and illustration of the features and spatial distributions of Circumpolar Deep Water (CDW) in the southern Indian Ocean. It is learnt from the comparison among the vertical distributions of temperature/salinity/oxygen along the 30°E, 90°E and 145°E sections respectively that some different features of CDW and the fronts can be found at those longitudes, and those differences can be attributed to the zonal transoceanic flow and the merizonal movement in the Circumpolar Deep Water. In fact, the zonal transoceanic flow is the main dynamic factor for the water exchange between the Pacific Ocean and the Indian Ocean or between the Atlantic Ocean and the Indian Ocean, and for the effects on the spatial distributions of the physical properties in CDW

Effects of spring low-temperature stress on winter wheat seed-setting characteristics of spike

Global climate change leads to frequent occurrence of low-temperature stress (LTS), which poses a serious threat to global food security. Here, environment-control phytotron experiments were conducted on cold-responsive cv. XM26 and cold-tolerant cv. YN19 during the anther differentiation period. Six LTS levels (4, 2, 0, -2, -4, -6 °C) and a control treatment (10 °C) were set to study the effects of different levels of LTS on wheat seed-setting characteristics and yield. LTS significantly decreased grain number per spike, 1 000-grain weight, and grain yield per plant (GYPP) of the two wheat cultivars. Each spike's grain number and weight distribution showed a quadratic curve, and the near-medium dominance of grain development was not affected by temperature. The grain number percentage and grain weight of wheat at different grain positions were G2 (2nd grain position) ≥ G1 (1st grain position) > G3 (3rd grain position) > G4 (4th grain position), in which G3 and G4 grain positions were more sensitive to LTS. In summary, LTS during the anther differentiation in wheat mainly led to a decrease in GYPP by significantly reducing the number and weight of inferior grains. Improving wheat cultivation measures and promoting the development of inferior grains are significant ways to prevent disasters and increase wheat quality and productivity in the future