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2019
Wang, X, Zhang GJ.  2019.  Evaluation of the quasi-biweekly oscillation over the South China Sea in early and late summer in CAM5. Journal of Climate. 32:69-84.   10.1175/jcli-d-18-0072.1   AbstractWebsite

Low-frequency intraseasonal oscillations in the tropical atmosphere in general circulation models (GCMs) were studied extensively in many previous studies. However, the simulation of the quasi-biweekly oscillation (QBWO), which is an important component of the intraseasonal oscillations, in GCMs has not received much attention. This paper evaluates the QBWO features over the South China Sea in early [May-June (MJ)] and late [August-September (AS)] summer in the National Center for Atmospheric Research (NCAR) Community Atmosphere Model, version 5.3 (CAM5), using observations and reanalysis data. Results show that the major features of the spatial distribution of the QBWO in both MJ and AS are simulated reasonably well by the model, although the amplitude of the variation is overestimated. CAM5 captures the local oscillation in MJ and the westward propagation in AS of the QBWO. Although there are important biases in geographical location and intensity in MJ, the model represents the QBWO horizontal and vertical structure qualitatively well in AS. The diagnosis of the eddy vorticity budget is conducted to better understand the QBWO activities in the model. Both horizontal advection of relative vorticity and that of planetary vorticity (Coriolis parameter) are important for the local evolution of the QBWO in MJ in observations as well as model simulation, whereas advection of planetary vorticity contributes to the westward propagation of QBWO vorticity anomalies in AS. Since the Coriolis parameter f only changes with latitude, this suggests that the correct simulation of anomalous meridional wind is a key factor in the realistic simulation of the QBWO in the model.

2018
Liu, YC, Fan JW, Xu KM, Zhang GJ.  2018.  Analysis of cloud-resolving model simulations for scale dependence of convective momentum transport. Journal of the Atmospheric Sciences. 75:2445-2472.   10.1175/jas-d-18-0019.1   AbstractWebsite

We use 3D cloud-resolving model (CRM) simulations of two mesoscale convective systems at midlatitudes and a simple statistical ensemble method to diagnose the scale dependency of convective momentum transport (CMT) and CMT-related properties and evaluate a parameterization scheme for the convection-induced pressure gradient (CIPG) developed by Gregory et al. Gregory et al. relate CIPG to a constant coefficient multiplied by mass flux and vertical mean wind shear. CRM results show that mass fluxes and CMT exhibit strong scale dependency in temporal evolution and vertical structure. The upgradient-downgradient CMT characteristics for updrafts are generally similar between small and large grid spacings, which is consistent with previous understanding, but they can be different for downdrafts across wide-ranging grid spacings. For the small to medium grid spacings (4-64 km), Gregory et al. reproduce some aspects of CIPG scale dependency except for underestimating the variations of CIPG as grid spacing decreases. However, for large grid spacings (128-512 km), Gregory et al. might even less adequately parameterize CIPG because it omits the contribution from either the nonlinear-shear or the buoyancy forcings. Further diagnosis of CRM results suggests that inclusion of nonlinear-shear forcing in Gregory et al. is needed for the large grid spacings. For the small to median grid spacings, a modified Gregory et al. with the three-updraft approach help better capture the variations of CIPG as grid spacing decreases compared to the single updraft approach. Further, the optimal coefficients used in Gregory et al. seem insensitive to grid spacings, but they might be different for updrafts and downdrafts, for different MCS types, and for zonal and meridional components.

Yang, MM, Zhang GJ, Sun DZ.  2018.  Precipitation and moisture in four leading CMIP5 models: Biases across large-scale circulation regimes and their attribution to dynamic and thermodynamic factors. Journal of Climate. 31:5089-5106.   10.1175/jcli-d-17-0718.1   AbstractWebsite

As key variables in general circulation models, precipitation and moisture in four leading models from CMIP5 (phase 5 of the Coupled Model Intercomparison Project) are analyzed, with a focus on four tropical oceanic regions. It is found that precipitation in these models is overestimated in most areas. However, moisture bias has large intermodel differences. The model biases in precipitation and moisture are further examined in conjunction with large-scale circulation by regime-sorting analysis. Results show that all models consistently overestimate the frequency of occurrence of strong upward motion regimes and peak descending regimes of 500-hPa vertical velocity JCLI-D-17-0718.1 regime, models produce too much precipitation compared to observation and reanalysis. But for moisture, their biases differ from model to model and also from level to level. Furthermore, error causes are revealed through decomposing contribution biases into dynamic and thermodynamic components. For precipitation, the contribution errors in strong upward motion regimes are attributed to the overly frequent . In the weak upward motion regime, the biases in the dependence of precipitation on probability density function (PDF) make comparable contributions, but often of opposite signs. On the other hand, the biases in column-integrated water vapor contribution are mainly due to errors in the frequency of occurrence of , while thermodynamic components contribute little. These findings suggest that errors in the frequency of occurrence are a significant cause of biases in the precipitation and moisture simulation.

2016
Wang, Y, Zhang GJ.  2016.  Global climate impacts of stochastic deep convection parameterization in the NCAR CAM5. Journal of Advances in Modeling Earth Systems. 8:1641-1656.   10.1002/2016ms000756   AbstractWebsite

In this study, the stochastic deep convection parameterization of Plant and Craig (PC) is implemented in the Community Atmospheric Model version 5 (CAM5) to incorporate the stochastic processes of convection into the Zhang-McFarlane (ZM) deterministic deep convective scheme. Its impacts on deep convection, shallow convection, large-scale precipitation and associated dynamic and thermodynamic fields are investigated. Results show that with the introduction of the PC stochastic parameterization, deep convection is decreased while shallow convection is enhanced. The decrease in deep convection is mainly caused by the stochastic process and the spatial averaging of input quantities for the PC scheme. More detrained liquid water associated with more shallow convection leads to significant increase in liquid water and ice water paths, which increases large-scale precipitation in tropical regions. Specific humidity, relative humidity, zonal wind in the tropics, and precipitable water are all improved. The simulation of shortwave cloud forcing (SWCF) is also improved. The PC stochastic parameterization decreases the global mean SWCF from 252.25 W/m(2) in the standard CAM5 to 248.86 W/m(2), close to 247.16 W/m(2) in observations. The improvement in SWCF over the tropics is due to decreased low cloud fraction simulated by the stochastic scheme. Sensitivity tests of tuning parameters are also performed to investigate the sensitivity of simulated climatology to uncertain parameters in the stochastic deep convection scheme.

Song, FF, Zhang GJ.  2016.  Effects of Southeastern Pacific sea surface temperature on the double-ITCZ bias in NCAR CESM1. Journal of Climate. 29:7417-7433.   10.1175/jcli-d-15-0852.1   AbstractWebsite

The double intertropical convergence zone (ITCZ) is a long-standing bias in the climatology of coupled general circulation models (CGCMs). The warm biases in southeastern Pacific (SEP) sea surface temperature (SST) are also evident in many CGCMs. In this study, the role of SEP SST in the double ITCZ is investigated by prescribing the observed SEP SST in the Community Earth System Model, version 1 (CESM1). Both the double ITCZ and dry equator problems are significantly improved with SEP SST prescribed. Both atmospheric and oceanic processes are involved in the improvements. The colder SST over the SEP decreases the precipitation, which enhances the southeasterly winds outside the prescribed SST region, cooling the ocean via increased evaporation. The enhanced descending motion over the SEP strengthens the Walker circulation. The easterly winds over the equatorial Pacific enhance upwelling and shoal the thermocline over the eastern Pacific. The changes of surface wind and wind curl lead to a weaker South Equatorial Countercurrent and stronger South Equatorial Current, preventing the warm water from expanding eastward, thereby improving both the double ITCZ and dry equator. The enhanced Walker circulation also increases the low-level wind convergence and reduces the wind speed in the tropical western Pacific, leading to warmer SST and stronger convection there. The stronger convection in turn leads to more cloud and reduces the incoming solar radiation, cooling the SST. These competing effects between radiative heat flux and latent heat flux make the atmospheric heat flux secondary to the ocean dynamics in the western Pacific warming.

Trammell, JH, Jiang X, Li LM, Kao A, Zhang GJ, Chang EKM, Yung Y.  2016.  Temporal and spatial variability of precipitation from observations and models*. Journal of Climate. 29:2543-2555.   10.1175/jcli-d-15-0325.1   AbstractWebsite

Principal component analysis (PCA) is utilized to explore the temporal and spatial variability of precipitation from GPCP and a CAM5 simulation from 1979 to 2010. In the tropical region, the interannual variability of tropical precipitation is characterized by two dominant modes (El Nino and El Nino Modoki). The first and second modes of tropical GPCP precipitation capture 31.9% and 15.6% of the total variance, respectively. The first mode has positive precipitation anomalies over the western Pacific and negative precipitation anomalies over the central and eastern Pacific. The second mode has positive precipitation anomalies over the central Pacific and negative precipitation anomalies over the western and eastern Pacific. Similar variations are seen in the first two modes of tropical precipitation from a CAM5 simulation, although the magnitudes are slightly weaker than in the observations. Over the Northern Hemisphere (NH) high latitudes, the first mode, capturing 8.3% of the total variance of NH GPCP precipitation, is related to the northern annular mode (NAM). During the positive phase of NAM, there are negative precipitation anomalies over the Arctic and positive precipitation anomalies over the midlatitudes. Over the Southern Hemisphere (SH) high latitudes, the first mode, capturing 13.2% of the total variance of SH GPCP precipitation, is related to the southern annular mode (SAM). During the positive phase of the SAM, there are negative precipitation anomalies over the Antarctic and positive precipitation anomalies over the midlatitudes. The CAM5 precipitation simulation demonstrates similar results to those of the observations. However, they do not capture both the high precipitation anomalies over the northern Pacific Ocean or the position of the positive precipitation anomalies in the SH.

2014
Suhas, E, Zhang GJ.  2014.  Evaluation of trigger functions for convective parameterization schemes using observations. Journal of Climate. 27:7647-7666.   10.1175/jcli-d-13-00718.1   AbstractWebsite

Realistic simulation of different modes of atmospheric variability ranging from diurnal cycle to interannual variation in global climate models (GCMs) depends crucially on the convection trigger criteria. In this study, using the data from constrained variational analysis by the Atmospheric System Research program for single-column models (SCM), the performance of the commonly used convective trigger functions in GCMs is evaluated based on the equitable threat score (ETS) value, a widely used forecast verification metric. From the ETS score, three consistently better-performing trigger functions were identified. They are based on the dilute and undilute convective available potential energy (CAPE) generation rate from large-scale forcing in the free troposphere (hereafter dCAPE) and parcel buoyancy at the lifting condensation level (Bechtold scheme). The key variables used to define these trigger functions are examined in detail. It is found that the dilute dCAPE trigger function performs the best consistently in both the tropical and midlatitude convective environment. Analysis of the composite fields of key variables of the trigger functions, based on the correct prediction, overprediction and underprediction of convection, and correct prediction of no-convection cases for convective onset, brings to light some critical factors responsible for the performance of the trigger functions. The lower-tropospheric advective forcing in dilute dCAPE trigger and vertical velocity in Bechtold trigger are identified to be the most importance ones. Suggestions are offered for further improvements.

Song, XL, Zhang GJ.  2014.  Role of climate feedback in El Nino-Like SST response to global warming. Journal of Climate. 27:7301-7318.   10.1175/jcli-d-14-00072.1   AbstractWebsite

Under global warming from the doubling of CO2, the equatorial Pacific experiences an El Nino-like warming, as simulated by most global climate models. A new climate feedback and response analysis method (CFRAM) is applied to 10 years of hourly output of the slab ocean model (SOM) version of the NCAR Community Climate System Model, version 3.0, (CCSM3-SOM) to determine the processes responsible for this warming. Unlike the traditional surface heat budget analysis, the CFRAM can explicitly quantify the contributions of each radiative climate feedback and of each physical and dynamical process of a GCM to temperature changes. The mean bias in the sum of partial SST changes due to each feedback derived with CFRAM in the tropical Pacific is negligible (0.5%) compared to the mean SST change from the CCSM3-SOM simulations, with a spatial pattern correlation of 0.97 between the two. The analysis shows that the factors contributing to the El Nino-like SST warming in the central Pacific are different from those in the eastern Pacific. In the central Pacific, the largest contributor to El Nino-like SST warming is dynamical advection, followed by PBL diffusion, water vapor feedback, and surface evaporation. In contrast, in the eastern Pacific the dominant contributor to El Nino-like SST warming is cloud feedback, with water vapor feedback further amplifying the warming.

2008
Boyle, J, Klein S, Zhang G, Xie S, Wei X.  2008.  Climate model forecast experiments for TOGA COARE. Monthly Weather Review. 136:808-832.   10.1175/2007mwr2145.1   AbstractWebsite

Short-term (1-10 day) forecasts are made with climate models to assess the parameterizations of the physical processes. The time period for the integrations is that of the intensive observing period (IOP) of the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE). The models used are the National Center for Atmospheric Research (NCAR) Community Climate Model, version 3.1 (CAM3.1); CAM3.1 with a modified deep convection parameterization; and the Geophysical Fluid Dynamics Laboratory (GFDL) Atmospheric Model, version 2 (AM2). The models were initialized using the state variables from the 40-yr ECMWF Re-Analysis (ERA-40). The CAM deep convective parameterization fails to demonstrate the sensitivity to the imposed forcing to simulate precipitation patterns associated with the Madden-Julian oscillations (MJOs) present during the period. AM2 and modified CAM3.1 exhibit greater correspondence to the observations at the TOGA COARE site, suggesting that convective parameterizations that have some type of limiter (as do AM2 and the modified CAM3.1) simulate the MJO rainfall with more fidelity than those without. None of the models are able to fully capture the correct phasing of westerly wind bursts with respect to precipitation in the eastward-moving MJO disturbance. Better representation of the diabatic heating and effective static stability profiles is associated with a better MJO simulation. Because the models' errors in the forecast mode bear a resemblance to the errors in the climate mode in simulating the MJO, the forecasts may allow for a better way to dissect the reasons for model error.

Li, G, Zhang GJ.  2008.  Understanding biases in shortwave cloud radiative forcing in the national center for atmospheric research community atmosphere model (CAM3) during El Nino. Journal of Geophysical Research-Atmospheres. 113   10.1029/2007jd008963   AbstractWebsite

This study aims to understand the weak response of shortwave cloud radiative forcing (SWCF) to El Nino in the NCAR CAM3. Observations from ERBE and CERES show strong negative SWCF in the central and eastern equatorial Pacific during El Nino. The standard CAM3 simulation at T42 resolution severely underestimates this response, with even wrong sign in the eastern Pacific. However, an experimental simulation at the same resolution, but with a modified convection parameterization scheme, simulates the cloud shortwave response to El Nino well, although the improvement in the eastern Pacific is not as significant as in the western and central Pacific. To unravel the mechanistic differences in SWCF response to El Nino between the two simulations, the authors analyze the cloud amount, cloud liquid water path (LWP), cloud ice water path (IWP), and convective and large-scale precipitation. It is shown that positive LWP anomalies are mainly responsible for the improved SWCF response to El Nino in the experimental simulation. Interaction among deep convection, shallow convection and low-level clouds is explored to explain this result. Negative LWP anomalies, largely due to reduced cloud water content and amount of low clouds during El Nino in the standard CAM3, weaken the SWCF response. Comparison with a higher-resolution simulation of CAM3 at T85 shows that the T85 simulation produces realistic SWCF response through greatly increased cloud water and ice content in the middle and upper troposphere, while reduced low-level cloud water content remains a problem.

2007
Collier, JC, Zhang GJ.  2007.  Effects of increased horizontal resolution on simulation of the North American monsoon in the NCAR CAM3: An evaluation based on surface, satellite, and reanalysis data. Journal of Climate. 20:1843-1861.   10.1175/jcl14099.1   AbstractWebsite

Simulation of the North American monsoon system by the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM3) is evaluated in its sensitivity to increasing horizontal resolution. For two resolutions, T42 and T85, rainfall is compared to Tropical Rainfall Measuring Mission (TRMM) satellite-derived and surface gauge-based rainfall rates over the United States and northern Mexico as well as rainfall accumulations in gauges of the North American Monsoon Experiment ( NAME) Enhanced Rain Gauge Network (NERN) in the Sierra Madre Occidental. Simulated upper-tropospheric mass and wind fields are compared to those from NCEP-NCAR reanalyses. The comparison presented herein demonstrates that tropospheric motions associated with the North American monsoon system are sensitive to increasing the horizontal resolution of the model. An increase in resolution from T42 to T85 results in changes to a region of large-scale midtropospheric descent found north and east of the monsoon anticyclone. Relative to its simulation at T42, this region extends farther south and west at T85. Additionally, at T85, the subsidence is stronger. Consistent with the differences in large-scale descent, the T85 simulation of CAM3 is anomalously dry over Texas and northeastern Mexico during the peak monsoon months. Meanwhile, the geographic distribution of rainfall over the Sierra Madre Occidental region of Mexico is more satisfactorily simulated at T85 than at T42 for July and August. Moisture import into this region is greater at T85 than at T42 during these months. A focused study of the Sierra Madre Occidental region in particular shows that, in the regional-average sense, the timing of the peak of the monsoon is relatively insensitive to the horizontal resolution of the model, while a phase bias in the diurnal cycle of monsoon season precipitation is somewhat reduced in the higher-resolution run. At both resolutions, CAM3 poorly simulates the month-to-month evolution of monsoon rainfall over extreme northwestern Mexico and Arizona, though biases are considerably improved at T85.

Wu, XQ, Deng LP, Song XL, Zhang GJ.  2007.  Coupling of convective momentum transport with convective heating in global climate simulations. Journal of the Atmospheric Sciences. 64:1334-1349.   10.1175/jas3894.1   AbstractWebsite

The effects of convective momentum transport (CMT) on global climate simulations are examined in this study. Comparison between two sets of 20-yr (1979-98) integration using the NCAR Community Climate Model version 3 (CCM3) illustrates that the inclusion of CMT in the convection scheme systematically modifies the climate mean state over the equatorial region. The convective momentum tendencies slow down the equatorward flow at higher latitudes near the surface and weaken the equatorial convergence and convection. This reduces the convective heating and drying around the equator and produces an improved meridional distribution within the upward branch of the Hadley circulation. The major heating peak during the boreal winter is moved to south of the equator at about 10 degrees S, which is closer to the heat budget residuals of the ECMWF reanalysis data. The responses of meridional wind to the reduced heating result in the secondary meridional circulation within the intertropical convergence zone.

2006
Zhang, GJ, Wang HJ.  2006.  Toward mitigating the double ITCZ problem in NCAR CCSM3. Geophysical Research Letters. 33   10.1029/2005gl025229   AbstractWebsite

The appearance of a spurious Inter-Tropical Convergence Zone south of the equator in the eastern and central equatorial Pacific, in addition to the observed one north of the equator, is a common problem in coupled global climate models. The present study investigates this "double ITCZ'' problem in the NCAR CCSM3. It shows that use of a modified Zhang-McFarlane convection scheme significantly mitigates the double ITCZ problem in boreal summer. This has a profound impact on the simulated sea surface temperature through cloud radiative forcing feedback. Both the warm bias in the southern ITCZ region and the cold bias in the cold tongue over the equator are reduced. Examination of the time series of precipitation, SST and surface energy fluxes shows that, depending on the convection parameterization used, double or single ITCZ emerges quickly within the first few months after the model start.

Mu, MQ, Zhang GJ.  2006.  Energetics of Madden-Julian oscillations in the National Center for Atmospheric Research Community Atmosphere Model version 3 (NCAR CAM3). Journal of Geophysical Research-Atmospheres. 111   10.1029/2005jd007003   AbstractWebsite

This study analyzes the tropical intraseasonal variability and associated Madden-Julian oscillations (MJO) simulated in the National Center for Atmospheric Research Climate Model CAM3 using two versions of the Zhang-McFarlane convection scheme. The results are compared with those from the Xie-Arkin observations and European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis. It is shown that modifications to the convection scheme in the model lead to substantial enhancement of the intraseasonal variability and MJO. The spatial scale of the precipitation anomalies associated with intraseasonal variability and MJO is also in better agreement with the Xie-Arkin observations and ECMWF reanalysis. By contrast the intraseasonal variability and MJO in the CAM3 are weak. The analysis of the energetics of intraseasonal variability shows that perturbation kinetic energy (PKE) and its sources and sinks through conversion from potential energy and mean flow and generation from wave energy flux are too strong in the modified CAM3 and too weak in the CAM3 when compared with the reanalysis. It also shows that different mechanisms are responsible for the PKE production in different locations. In convectively active regions, conversion from potential energy and vertical transport are important to the maintenance of the upper troposphere PKE; in convectively suppressed regions, horizontal wave energy flux convergence and barotropic conversion are important. The interaction between convection and large-scale circulation plays an important role in the maintenance of intraseasonal variability and MJO through PKE conversion from potential energy generated by convective heating.

1996
Zhang, GJ, Grossman RL.  1996.  Surface evaporation during the central equatorial Pacific experiment: A climate-scale perspective. Journal of Climate. 9:2522-2537.   10.1175/1520-0442(1996)009<2522:sedtce>2.0.co;2   AbstractWebsite

This study is directed to evaluating the feedback between evaporation (F-L) and sea surface temperature (T-s) in the equatorial Pacific Ocean by looking at the components that control dF(L)/dT(s), the variation of evaporation with T-s. First eddy correlation evaporation estimates obtained during long (similar to 1000-1500 km), low-level (30 m) traverses of the central equatorial Pacific by research aircraft during the Central Equatorial Pacific Experiment (CEPEX) are analyzed. From this limited dataset, extension to climate space- and timescales is made by comparing the aircraft measurements to bulk aerodynamic estimates to F-L using mean values from both the aircraft and Tropical Atmosphere-Ocean buoys. Variation of surface evaporation with T-s is shown to be affected not only to surface saturation humidity deficit and its dependence on T-s, but also by variations of wind speed with T-s. Depending on the relative importance of the two contributions, surface evaporation can either increase or decrease with T-s. Intercomparison between the aircraft data and the buoy data indicates that the humidity deficit effect is dominant during CEPEX, and in low T-s, where surface winds are only weakly related to T-s: the effect of wind speed variation with T-s is much more important in the 2-yr buoy data for T-s greater than or equal to 301 K. The discrepancy between the evaporation feedback in CEPEX and that from the 2-yr buoy data is shown to be largely due to oversampling of high winds and high evaporation during CEPEX for 302 less than or equal to T, < 303 K. The long-term buoy data show that for T-s < 301 K, dF(L)/dT(s) = +9 W m(-2) K-1, while for 304 K > T-c greater than or equal to 301 K, dF(L)/dT(s) = -13 W m(-2) K-1. Furthermore, observations of F-L are well below the values necessary for evaporation to be the primary limiting factor in the regulation of T-s in the equatorial Pacific.

1995
Zhang, GJ, McPhaden MJ.  1995.  The relationship between sea surface temperature and latent heat flux in the equatorial Pacific. Journal of Climate. 8:589-605.   10.1175/1520-0442(1995)008<0589:trbsst>2.0.co;2   AbstractWebsite

Moored buoy data from the equatorial Pacific are analyzed to investigate the relationship between sea surface temperature (SST) and latent heat flux from the ocean. It is found that at low SST the latent heat flux increases with SST; at high SST the latent heat flux decreases with increasing SST, a relationship that cannot be explained by thermodynamic considerations alone, Analysis of the wind speeds and humidity differences between the surface air and the saturation humidity at the sea surface temperature indicates that while at low SST the humidity difference primarily determines the latent heat flux, and at high SST a sharp decrease in wind speed is mostly responsible for the low latent heat flux. A mechanism that leads to low latent heat flux at high SST is suggested; it involves the interaction between convection and the large-scale circulation. The longitudinal distribution of SST, wind speed, humidity difference, and latent heat flux is found to be similar to that in previous studies. In the eastern Pacific, SST is the lowest, the wind speed is large, and the humidity difference is low; in the western Pacific, SST is the highest, whereas the wind speed is low and the humidity difference is large. Latent heat flux increases from the eastern Pacific westward, reaching a maximum in the central Pacific, and then decreases toward the western Pacific warm pool. Through analyses of the data on different timescales, we found that the atmospheric processes leading to low latent heat flux over warm SST were mainly operative on seasonal timescales (periods longer than 90 days). On shorter timescales (periods of 30-90 days), the influence of intraseasonal Madden and Julian waves was evident. On this timescale, the relationship between SST and latent heat flux was characterized by a 10-day lag between atmospheric forcing (primarily related to winds) and the local oceanic response in the western and central Pacific. In the eastern Pacific cold tongue, SST and latent heat flux variations were nearly in phase on this timescale, indicating an atmospheric response to oceanic forcing. For periods less than 30 days, SST variations associated with tropical instability waves were likewise shown to be important in forcing latent heat flux variations in the eastern Pacific cold tongue.

Ramanathan, V, Subasilar B, Zhang GJ, Conant W, Cess RD, Kiehl JT, Grassl H, Shi L.  1995.  Warm pool heat budget and shortwave cloud forcing: a missing physics? Science. 267:499-503.   10.1126/science.267.5197.499   AbstractWebsite

Ship observations and ocean models indicate that heat export from the mixed layer of the western Pacific warm pool is small (<20 watts per square meter). This value was used to deduce the effect of clouds on the net solar radiation at the sea surface. The inferred magnitude of this shortwave cloud forcing was large (approximate to-100 watts per square meter) and exceeded its observed value at the top of the atmosphere by a factor of about 1.5, This result implies that clouds (at least over the warm pool) reduce net solar radiation at the sea surface not only by reflecting a significant amount back to space, but also by trapping a large amount in the cloudy atmosphere, an inference that is at variance with most model results. The excess cloud absorption, if confirmed, has many climatic implications, including a significant reduction in the required tropics to extratropics heat transport in the oceans.