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A new high-resolution Regional Earth System Model, namely ROM, has been implemented over CORDEX-SA towards examining the impact of air–sea coupling on the Indian summer monsoon characteristics. ROM's simulated mean ISM rainfall and associated dynamical and thermodynamical processes, including the representation of northward and eastward propagating convention bands, are closer to observation than its standalone atmospheric model component (REMO), highlighting the advantage of air–sea coupling. However, the value addition of air–sea coupling varies spatially with more significant improvements over regions with large biases. Bay of Bengal and the eastern equatorial Indian Ocean are the most prominent region where the highest added value is observed with a significant reduction up to 50–500% precipitation bias. Most of the changes in precipitation over the ocean are associated with convective precipitation (CP) due to the suppression of convective activity caused by the negative feedback due to the inclusion of air–sea coupling. However, CP and large-scale precipitation (LP) improvements show east–west asymmetry over the Indian land region. The substantial LP bias reduction is noticed over the wet bias region of western central India due to its suppression, while enhanced CP over eastern central India contributed to the reduction of dry bias. An insignificant change is noticed over Tibetan Plateau, northern India, and Indo Gangetic plains. The weakening of moisture-laden low-level Somalia Jets causes the diminishing of moisture supply from the Arabian Sea (AS) towards Indian land regions resulting in suppressed precipitation, reducing wet bias, especially over western central India. The anomalous high kinetic energy over AS, wind shear, and tropospheric temperature gradient in REMO compared to observation is substantially reduced in the ROM, facilitating the favourable condition for suppressing moisture feeding and hence the wet bias over west-central India in ROM. The warmer midlatitude in ROM than REMO over eastern central India strengthens the convection, enhancing precipitation results in reducing the dry bias. Despite substantially improved ROM'performance, it still exhibits some systematic biases (wet/dry) partially associated with the persistent warm/cold SST bias and land–atmosphere interaction. [ABSTRACT FROM AUTHOR]

In this work we use a regional atmosphere–ocean coupled model (RAOCM) and its stand-alone atmospheric component to gain insight into the impact of atmosphere–ocean coupling on the climate change signal over the Iberian Peninsula (IP). The IP climate is influenced by both the Atlantic Ocean and the Mediterranean sea. Complex interactions with the orography take place there and high-resolution models are required to realistically reproduce its current and future climate. We find that under the RCP8.5 scenario, the generalized 2-m air temperature (T2M) increase by the end of the twenty-first century (2070–2099) in the atmospheric-only simulation is tempered by the coupling. The impact of coupling is specially seen in summer, when the warming is stronger. Precipitation shows regionally-dependent changes in winter, whilst a drier climate is found in summer. The coupling generally reduces the magnitude of the changes. Differences in T2M and precipitation between the coupled and uncoupled simulations are caused by changes in the Atlantic large-scale circulation and in the Mediterranean Sea. Additionally, the differences in projected changes of T2M and precipitation with the RAOCM under the RCP8.5 and RCP4.5 scenarios are tackled. Results show that in winter and summer T2M increases less and precipitation changes are of a smaller magnitude with the RCP4.5. Whilst in summer changes present a similar regional distribution in both runs, in winter there are some differences in the NW of the IP due to differences in the North Atlantic circulation. The differences in the climate change signal from the RAOCM and the driving Global Coupled Model show that regionalization has an effect in terms of higher resolution over the land and ocean. [ABSTRACT FROM AUTHOR]

The tropical Atlantic Ocean receives an important freshwater supply from river runoff and from precipitation in the intertropical convergence zone. It results in a strong salinity stratification that may influence vertical mixing, and thus sea surface temperature (SST) and air–sea fluxes. The aim of this study is to assess the impact of salinity stratification on the tropical Atlantic surface variables. This is achieved through comparison among regional 1/4 ∘ coupled ocean–atmosphere simulations for which the contribution of salinity stratification in the vertical mixing scheme is included or discarded. The analysis reveals that the strong salinity stratification in the northwestern tropical Atlantic induces a significant increase of SST (0.2 ∘ C–0.5 ∘ C) and rainfall (+ 19%) in summer, hereby intensifying the ocean–atmosphere water cycle, despite a negative atmospheric feedback. Indeed, the atmosphere dampens the oceanic response through an increase in latent heat loss and a reduction of shortwave radiation reaching the ocean surface. In winter, the impacts of salinity stratification are much weaker, most probably because of a deeper mixed layer at this time. In the equatorial region, we found that salinity stratification induces a year-round shoaling of the thermocline, reinforcing the cold tongue cool anomaly in summer. The concept of barrier layer has not been identified as relevant to explain the SST response to salinity stratification in our region of interest. [ABSTRACT FROM AUTHOR]

Tibetan Plateau (TP) summer precipitation, whose first leading mode presents a dipole oscillation between the northeastern and southeastern TP, plays important roles in the water cycle and atmospheric circulation. Using a weakly coupled data assimilation (WCDA) system to constrain the atmospheric component in a coupled model with a global atmospheric reanalysis product, this study demonstrates significant improvements in predicting the interannual variation of summer precipitation over the eastern TP, capturing the strong reversal mode between the northeastern and southeastern TP. These improvements are mainly attributed to the strong air–sea coupling over the North Atlantic (NA) and its remote impacts on the TP precipitation. This coupling allows observation-constrained atmosphere to significantly influence initial conditions (ICs) of sea surface temperature (SST) in the NA area and then obviously affect predictions of both NA SST and summer North Atlantic Oscillation (SNAO), which affects the downstream TP atmospheric circulation through the wave train of Eliassen-Palm (EP) stationary wave flux. This study highlights the importance of NA air–sea coupling in the interannual predictability of TP precipitation and suggests a new source of interannual predictability of TP precipitation. [ABSTRACT FROM AUTHOR]

The roles of air–sea coupling and horizontal resolution in the representation of Indian monsoon low pressure systems (LPS) in Met Office Unified Model (MetUM) global climate simulations are investigated. To avoid the generally large sea surface temperature (SST) biases in standard coupled atmosphere–ocean global climate models (GCMs), the analysis is performed on experiments from an atmosphere model coupled to a mixed-layer ocean model (MetUM-GOML2), which allows coupling to be applied regionally as well as globally, while constraining the ocean mean state in coupled regions. Compared to the standard AMIP-style MetUM atmosphere-only simulations, the MetUM-GOML2 simulations produce more monsoon LPS, which is attributed to effects of relatively small remaining (Indian Ocean) SST biases that somewhat strengthen the atmospheric monsoon base state. However, the MetUM-GOML2 simulations, all starting from the same atmospheric and oceanic base state, allow for an idealised approach to evaluate the relative effects of coupling and resolution. When the effects of SST biases are excluded, global coupling has a neutral impact on the number of LPS formed, while the associated rainfall is somewhat reduced due to a local negative air–sea feedback reducing the strength of atmospheric convection and weakening individual LPS. The MetUM-GOML2 simulations show particular sensitivity to localised coupling in the Indian and Pacific Oceans, which appears to enhance the effect of monsoon LPS. Although, in contrast to the global coupling comparison, the comparison of regionally coupled simulations is affected by both differences in interannual SST variability and SST biases, and it is likely that this causes at least part of the positive effects from Indian and Pacific Ocean coupling. More importantly, however, is that the effects of air–sea coupling are substantially smaller than the positive effects of the increase in horizontal resolution from N96 (approx. 200 km) to N216 (approx. 90 km). The resolution effect is also larger than that seen in older MetUM configurations. [ABSTRACT FROM AUTHOR]

The climate variability in the Western North Pacific (WNP), which is surrounded by densely populated countries, is closely tied to the lives of the people in the East Asia in terms of climate and socioeconomics. Along with global warming, remarkable interannual and interdecadal variations in sea surface temperature (SST) and sea surface height have been observed in the WNP. Here we demonstrated that boreal summer SST variability in the western hemisphere warm pool (WHWP, a.k.a. Atlantic Warm Pool) near the Intra-Americas Sea, which is known as the second largest warm pool on the planet, has considerably contributed to the climate variability in the WNP in subsequent winter. This is possible due to westward propagation of Rossby waves associated with a WHWP-SST warming (cooling) in mid-summer to early fall season, which induces northerly (southerly) wind anomalies over the North Pacific. In the presence of northeasterly mean trade winds, the anomalous meridional winds interact with SST and precipitation anomalies. Such air-sea coupling processes gradually move equatorward and westward along the climatological migration of the Pacific Intertropical Convergence Zone, and it has finally an effect on the climate variability over the WNP in winter. Further diagnosis verifies that WHWP-WNP connection exists not only on interannual time scale but also on decadal time scale. The analysis using state-of-the-art climate models reasonably supports this argument. A better understanding of the WHWP influence is expected to improve forecasts for the WNP climate and assist socioeconomic development in the East Asia. [ABSTRACT FROM AUTHOR]

Low-frequency variations of typhoon paths are often attributed to changes in the North Pacific subtropical high and monsoon through influences on the steering wind. Evidence indicates however a strong imprint of the Kuroshio on the atmosphere. Here we show that the meridional oscillation of sea surface temperature (SST) front over the Kuroshio Extension east of Japan significantly correlates with the number of land-falling typhoons along East Asia from June to October, accounting for 70% of the low-frequency variance since 1980. We used observations and a simple model to show that when the SST front shifts poleward (equatorward), SST gradient south of the current and westerly tropospheric wind weaken (strengthen), steering more typhoons to veer toward (away from) the East Asian continent. Our analysis also indicates that long-term weakening of SST gradient and westerly wind appears to be concomitant with poleward shifting of the Kuroshio, attributed to global warming in some studies, and suggests the potential for more land-falling typhoons in East Asia in the coming decades. [ABSTRACT FROM AUTHOR]

Based on the conventional weather research and forecasting (WRF) model and the air-sea coupled mode WRF-OMLM, we investigate the potential regulation on the climatic effect of Tibetan Plateau (TP) heating by the air-sea coupling over the tropical Indian Ocean and western Pacific. Results indicate that the TP heating significantly enhances the southwesterly monsoon circulation over the northern Indian Ocean and the South Asia subcontinent. The intensified southwesterly wind cools the sea surface mainly through the wind-evaporation-SST (sea surface temperature) feedback. Cold SST anomaly then weakens monsoon convective activity, especially that over the Bay of Bengal, and less water vapor is thus transported into the TP along its southern slope from the tropical oceans. As a result, summer precipitation decreases over the TP, which further weakens the TP local heat source. Finally, the changed TP heating continues to influence the summer monsoon precipitation and atmospheric circulation. To a certain extent, the air-sea coupling over the adjacent oceans may weaken the effect of TP heating on the mean climate in summer. It is also implied that considerations of air-sea interaction are necessary in future simulation studies of the TP heating effect. [ABSTRACT FROM AUTHOR]

This paper assesses the impact of air-sea coupling on Indian Ocean tropical cyclones (TCs) by comparing a 20-year long simulation of a ¼° regional coupled ocean-atmosphere model with a twin experiment, where the atmospheric component is forced by sea surface temperature from the coupled simulation. The coupled simulation reproduces the observed spatio-temporal TCs distribution and TC-induced surface cooling reasonably well, but overestimates the number of TCs. Air-sea coupling does not affect the cyclogenesis spatial distribution but reduces the number of TCs by ~ 20% and yields a better-resolved bimodal seasonal distribution in the northern hemisphere. Coupling also affects intensity distribution, inducing a four-fold decrease in the proportion of intense TCs (Cat-2 and stronger). Air-sea coupling damps TCs growth through a reduction of inner-core upward enthalpy fluxes due to the TC-induced cooling. This reduction is particularly large for the most intense TCs of the northern Indian Ocean (up to 250 W m−2), due to higher ambient surface temperatures and larger TC-induced cooling there. The negative feedback of air-sea coupling on strongest TCs is mainly associated with slow-moving storms, which spend more time over the cold wake they induce. Sensitivity experiments using a different convective parameterization yield qualitatively similar results, with a larger (~ 65%) reduction in the number of TCs. Because of their relatively coarse resolution (¼°), both set of experiments however fail to reproduce the most intense observed TCs. Further studies with finer resolution models in the Bay of Bengal will be needed to assess the expectedly large impact of air-sea coupling on those intense and deadly TCs. [ABSTRACT FROM AUTHOR]

Climate modeling groups nowadays develop earth system models (ESMs) by incorporating biogeochemical processes in their climate models. The ESMs, however, often show substantial bias in simulated marine biogeochemistry which can potentially introduce an undesirable bias in physical ocean fields through biogeophysical interactions. This study examines how and how much the chlorophyll bias in a state-of-the-art ESM affects the mean and seasonal cycle of tropical Pacific sea-surface temperature (SST). The ESM used in the present study shows a sizeable positive bias in the simulated tropical chlorophyll. We found that the correction of the chlorophyll bias can reduce the ESM’s intrinsic cold SST mean bias in the equatorial Pacific. The biologically-induced cold SST bias is strongly affected by seasonally-dependent air-sea coupling strength. In addition, the correction of chlorophyll bias can improve the annual cycle of SST by up to 25%. This result suggests a possible modeling approach in understanding the two-way interactions between physical and chlorophyll biases by biogeophysical effects. [ABSTRACT FROM AUTHOR]

This study introduces a new approach to investigate the potential effects of air-sea coupling on simulated precipitation inland over Central Europe. We present an inter-comparison of two regional climate models (RCMs), namely, the COSMO-CLM (hereafter CCLM) and RCA4 models, which are configured for the EURO-CORDEX domain in the coupled and atmosphere-only modes. Two versions of the CCLM model, namely, 4.8 and 5.0, join the inter-comparison being almost two different models while providing pronouncedly different summer precipitation simulations because of many changes in the dynamics and physics of CCLM in version 5.0. The coupling effect on the prominent summer dry bias over Central Europe is analysed using seasonal (JJA) mean statistics for the 30-year period from 1979 to 2009, with a focus on extreme precipitation under specific weather regimes. The weather regimes are compared between the coupled and uncoupled simulations to better understand the mechanism of the coupling effects. The comparisons of the coupled systems with the atmosphere-only models show that coupling clearly reduces the dry bias over Central Europe for CCLM 4.8, which has a large dry summer bias, but not for CCLM 5.0 and RCA4, which have smaller dry biases. This result implies that if the atmosphere-only model already yields reasonable summer precipitation over Central Europe, not much room for improvement exists that can be caused by the air-sea coupling over the North Sea and the Baltic Sea. However, if the atmosphere-only model shows a pronounced summer dry bias because of a lack of moisture transport from the seas into the region, the considered coupling may create an improved simulation of summer precipitation over Central Europe, such as for CCLM 4.8. For the latter, the benefit of coupling varies over the considered timescales. The precipitation simulations that are generated by the coupled system COSTRICE 4.8 and the atmosphere-only CCLM 4.8 are mostly identical for the summer mean. However, the COSTRICE simulations are generally more accurate than the atmosphere-only CCLM simulations if extreme precipitation is considered, particularly under Northerly Circulation conditions, in which the airflow from the North Atlantic Ocean passes the North Sea in the coupling domain. The air-sea feedback (e.g., wind, evaporation and sea surface temperature) and land-sea interactions are better reproduced with the COSTRICE model system than the atmosphere-only CCLM and lead to an improved simulation of large-scale moisture convergence from the sea to land and, consequently, increased heavy precipitation over Central Europe. [ABSTRACT FROM AUTHOR]

Eight weather types (WTs) are computed over 98.75°W-56.25°W, 8.75°N-31.25°N using cluster analysis of daily low-level (925 hPa) winds and outgoing longwave radiation, without removing the mean annual cycle, by a k-means algorithm from 1979 to 2013. The WTs can be firstly interpreted as snapshots of the annual cycle with a clear distinction between 5 'wintertime' and 3 'summertime' WTs, which account together for 70 % of the total mean annual rainfall across the studied domain. The wintertime WTs occur mostly from late November to late April and are characterized by varying intensity and location of the North Atlantic subtropical high (NASH) and transient synoptic troughs along the northern edge of the domain. Large-scale subsidence dominates the whole basin but rainfall can occur over sections of the basin, especially on the windward shores of the troughs associated with the synoptic waves. The transition between wintertime and summertime WTs is rather abrupt, especially in May. One summertime WT (WT 4) is prevalent in summer, and almost exclusive around late July. It is characterized by strong NASH, fast Caribbean low level jet and rainfall mostly concentrated over the Caribbean Islands, the Florida Peninsula, the whole Central America and the tropical Eastern Pacific. The two remaining summertime WTs display widespread rainfall respectively from Central America to Bermuda (WT 5) and over the Eastern Caribbean (WT 6). Both WTs combine reduced regional scale subsidence and weaker Caribbean low-level jet relatively to WT 4. The relationships between WT frequency and El Niño Southern Oscillation (ENSO) events are broadly linear. Warm central and eastern ENSO events are associated with more WT 4 (less WT 5-6) during boreal summer and autumn (0) while this relationship is reversed during boreal summer (+1) for central events only. In boreal winter, the largest anomalies are observed for two WTs consistent with negative (WT 2) and positive (WT 8) phases of the North Atlantic Oscillation; more (less) WT 2 and less (more) WT 8 than usually occur from January to early April during warm (cold) ENSO events, the strongest anomalies being recorded during eastern events. Multinomial logistic regression is used to hindcast the 11-day low-pass filtered occurrence of WTs from local (Caribbean Sea and Gulf of Mexico) and remote (Eastern and Central Tropical Pacific) sea surface temperatures (SSTs). In boreal summer, the interannual variability of the seasonal occurrence of WTs 4-6 is well hindcast when at least the Caribbean Sea and Eastern Tropical Pacific are included as predictors with anomalously warm (cold) SSTs over the Caribbean Sea (Eastern Tropical Pacific) being related to more WT 5-6 and less WT 4 and vice-versa. Using antecedent SST to forecast WT frequency shows that the SST forcing is negligible at the start of boreal summer and increases toward its end. [ABSTRACT FROM AUTHOR]

Marine heat waves along the Western Australian coast are potentially damaging to the marine environment especially coastal fisheries and the Ningaloo Reef. Initiation and amplification mechanisms for marine heat waves (referred to as 'Ningaloo Niño' events) are explored using ocean and atmosphere reanalyses for the period 1960-2011. We find that the onset stage from October to November is promoted by wind-evaporation-SST feedback that operates to the northwest of the coast on the north-eastern flank of the Mascarene subtropical high: cyclonic anomalies act to reduce the surface wind speed and warm the ocean surface, thereby driving increased rainfall and stronger cyclonic anomalies. The growth and southward expansion of positive SST anomalies along the Australian west coast is further supplemented by anomalous poleward advection of heat by the Leeuwin Current, which is coupled with the cyclonic anomalies off the coast. The strongest Ningaloo Niño events, such as the record strong 2011 event, occur in conjunction with La Niña conditions in the Pacific, which drives westerly wind anomalies to the northwest of Australia that can promote the WES feedback and accelerate the Leeuwin Current via transmission of thermocline anomalies from the western Pacific onto the west Australian coast. However, many Ningaloo Niño events occur independent of La Niña and some Ningaloo Niño events even occur during certain El Niños. We explain this general independence from ENSO because the triggering of Ningaloo Niño events from the Pacific is most sensitive to antecedent SST anomalies in the far western Pacific, rather than in the central Pacific where ENSO typically has greatest magnitude. [ABSTRACT FROM AUTHOR]

Strong sea surface temperature fronts in open seas are known to affect the atmosphere. Shelf-sea fronts in winter have comparable strengths, yet their impacts on winds have not been studied. In January of 2012, a persistent, narrow band of cloud stretching 600-1,000 km was observed along the front of East China Sea (ECS). Numerical and analytical models show that the cloud was formed atop a recirculating cell induced by the front and, more generally, that β-plumes of low and high pressures emanate and spread far from fronts. Consistent with the theory, observations show that in ECS at inter-annual time scales, strong fronts co-vary with on-shelf convergent wind, strong northeasterly monsoon, and alongshelf alignment of clouds with low clouds near the coast and higher clouds offshore. Our results suggest that shelf-sea fronts are potentially an important dynamic determinant of climate variability of East Asia. [ABSTRACT FROM AUTHOR]

The Mediterranean Sea water budget (MWB) is a key parameter, as it controls the Mediterranean Sea water loss and thus the Atlantic Water inflow and the Mediterranean general circulation. More accurately, the MWB controls the net flow through the Strait of Gibraltar, which implies both inflow and outflow. Generally considered at the basin scale and over long-term periods, the MWB is in fact characterized by a large variability in space and time, induced by the complex topography of the region, mesoscale processes and (short) intense events in the ocean and atmosphere compartments. In this study, we use an ocean-atmosphere coupled system at mesoscale able to represent such phenomena, to evaluate the MWB atmospheric components: Evaporation (E) and Precipitation (P). We compare two companion regional simulations: an uncoupled atmospheric run using the ERA-interim Sea Surface Temperature (SST) reanalysis and a coupled run using the MORCE system with the two-way coupling between the NEMO-MED12 eddy-resolving ocean model and the non-hydrostatic Weather Research and Forecasting atmospheric model. We first evaluate the SST validity against satellite data and evidence the coupled system ability in representing SST mesoscale structures, characteristics of the Mediterranean circulation and of small-scale ocean processes, despite a colder mean value and a lower amplitude of the annual cycle. Then, the comparison aims to examine the coupled processes effects (meaning the impacts of the interactive high-resolution and high-frequency SST) on E and P and on their variability. The comparison highlights that the SST is the controlling factor for E and P budgets, with reduction by 6 and 3 % in the coupled run compared to the uncoupled run, respectively. The modifications propagate until 750 km inland far from the Mediterranean coast, as towards the Atlantic Ocean and the Black Sea. This indicates that coupling plays a major role in distributing water at mesoscale. The coupling directly modifies the seasonal variability. It also significantly decreases extreme evaporation and precipitation occurences and intensities. This extreme events mitigation in the coupled run contributes for ~50 % to the decrease in the E and P budgets. [ABSTRACT FROM AUTHOR]

This study presents the first multidecadal and coupled regional simulation of cyclonic activity in the South Pacific. The long-term integration of state-of the art models provides reliable statistics, missing in usual event studies, of air-sea coupling processes controlling tropical cyclone (TC) intensity. The coupling effect is analyzed through comparison of the coupled model with a companion forced experiment. Cyclogenesis patterns in the coupled model are closer to observations with reduced cyclogenesis in the Coral Sea. This provides novel evidence of air-sea coupling impacting not only intensity but also spatial cyclogenesis distribution. Storm-induced cooling and consequent negative feedback is stronger for regions of shallow mixed layers and thin or absent barrier layers as in the Coral Sea. The statistical effect of oceanic mesoscale eddies on TC intensity (crossing over them 20 % of the time) is also evidenced. Anticyclonic eddies provide an insulating effect against storm-induced upwelling and mixing and appear to reduce sea surface temperature (SST) cooling. Cyclonic eddies on the contrary tend to promote strong cooling, particularly through storm-induced upwelling. Air-sea coupling is shown to have a significant role on the intensification process but the sensitivity of TCs to SST cooling is nonlinear and generally lower than predicted by thermodynamic theories: about 15 rather than over 30 hPa °C and only for strong cooling. The reason is that the cooling effect is not instantaneous but accumulated over time within the TC inner-core. These results thus contradict the classical evaporation-wind feedback process as being essential to intensification and rather emphasize the role of macro-scale dynamics. [ABSTRACT FROM AUTHOR]

The present study assesses the forecast skill of the Madden-Julian Oscillation (MJO) observed during the period of DYNAMO (Dynamics of the MJO)/CINDY (Cooperative Indian Ocean Experiment on Intraseasonal Variability in Year 2011) field campaign in the GFS (NCEP Global Forecast System), CFSv2 (NCEP Climate Forecast System version 2) and UH (University of Hawaii) models, and revealed their strength and weakness in forecasting initiation and propagation of the MJO. Overall, the models forecast better the successive MJO which follows the preceding event than that with no preceding event (primary MJO). The common modeling problems include too slow eastward propagation, the Maritime Continent barrier and weak intensity. The forecasting skills of MJO major modes reach 13, 25 and 28 days, respectively, in the GFS atmosphere-only model, the CFSv2 and UH coupled models. An equal-weighted multi-model ensemble with the CFSv2 and UH models reaches 36 days. Air-sea coupling plays an important role for initiation and propagation of the MJO and largely accounts for the skill difference between the GFS and CFSv2. A series of forecasting experiments by forcing UH model with persistent, forecasted and observed daily SST further demonstrate that: (1) air-sea coupling extends MJO skill by about 1 week; (2) atmosphere-only forecasts driven by forecasted daily SST have a similar skill as the coupled forecasts, which suggests that if the high- resolution GFS is forced with CFSv2 forecasted daily SST, its forecast skill can be much higher than its current level as forced with persistent SST; (3) atmosphere-only forecasts driven by observed daily SST reaches beyond 40 days. It is also found that the MJO-TC (Tropical Cyclone) interactions have been much better represented in the UH and CFSv2 models than that in the GFS model. Both the CFSv2 and UH coupled models reasonably well capture the development of westerly wind bursts associated with November 2011 MJO and the cyclogenesis of TC05A in the Indian Ocean with a lead time of 2 weeks. However, the high-resolution GFS atmosphere-only model fails to reproduce the November MJO and the genesis of TC05A at 2 weeks' lead. This result highlights the necessity to get MJO right in order to ensure skillful extended-range TC forecasting. [ABSTRACT FROM AUTHOR]

Associated with the double 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 inherent in many contemporary coupled models. Based on a newly-developed coupled model, we performed a control run and two sensitivity runs, one is a coupled run with annual mean SST correction and the other is an ocean forced run. By comparison of these three runs, we demonstrated that a serious consequence of this SST bias is to severely suppress the thermocline feedback in a realistic simulation of the El Niño/Southern Oscillation. Firstly, the excessive cold tongue extension pushes the anomalous convection far westward from the equatorial central Pacific, prominently diminishing the convection-low level wind feedback and thus the air-sea coupling strength. Secondly, the equatorial surface wind anomaly exhibits a relatively uniform meridional structure with weak gradient, contributing to a weakened wind-thermocline feedback. Thirdly, the equatorial cold SST bias induces a weakened upper-ocean stratification and thus yields the underestimation of the thermocline-subsurface temperature feedback. Finally, the dipole SST bias underestimates the mean upwelling through (a) undermining equatorial mean easterly wind stress, and (b) enhancing convective mixing and thus reducing the upper ocean stratification, which weakens vertical shear of meridional currents and near-surface Ekman-divergence. [ABSTRACT FROM AUTHOR]

The effects of air-sea coupling over the tropical Indian Ocean (TIO) on the eastward- and northward-propagating boreal summer intraseasonal oscillation (BSISO) are investigated by comparing a fully coupled (CTL) and a partially decoupled Indian Ocean (pdIO) experiment using SINTEX-F coupled GCM. Air-sea coupling over the TIO significantly enhances the intensity of both the eastward and northward propagations of the BSISO. The maximum spectrum differences of the northward- (eastward-) propagating BSISO between the CTL and pdIO reach 30% (25%) of their respective climatological values. The enhanced eastward (northward) propagation is related to the zonal (meridional) asymmetry of sea surface temperature anomaly (SSTA). A positive SSTA appears to the east (north) of the BSISO convection, which may positively feed back to the BSISO convection. In addition, air-sea coupling may enhance the northward propagation through the changes of the mean vertical wind shear and low-level specific humidity. The interannual variations of the TIO regulate the air-sea interaction effect. Air-sea coupling enhances (reduces) the eastward-propagating spectrum during the negative Indian Ocean dipole (IOD) mode, positive Indian Ocean basin (IOB) mode and normal years (during positive IOD and negative IOB years). Such phase dependence is attributed to the role of the background mean westerly in affecting the wind-evaporation-SST feedback. A climatological weak westerly in the equatorial Indian Ocean can be readily reversed by anomalous zonal SST gradients during the positive IOD and negative IOB events. Although the SSTA is always positive to the northeast of the BSISO convection for all interannual modes, air-sea coupling reduces the zonal asymmetry of the low-level specific humidity and thus the eastward propagation spectrum during the positive IOD and negative IOB modes, while strengthening them during the other modes. Air-sea coupling enhances the northward propagation under all interannual modes due to the persistent westerly monsoon flow over the northern Indian Ocean. [ABSTRACT FROM AUTHOR]