The Effect of an Equatorial Continent on the Tropical Rain Belt. Part 1: Annual Mean Changes in the ITCZ

2021 ◽  
pp. 1-51
Author(s):  
Michela Biasutti ◽  
Rick D. Russotto ◽  
Aiko Voigt ◽  
Charles C. Blackmon-Luca
Keyword(s):  
Heat Capacity ◽  
Surface Energy Budget ◽  
Cold Tongue ◽  
Evaporative Resistance ◽  
Anomalous Surface ◽  
Oceanic Climate ◽  
Double Itcz ◽  
Intercomparison Project ◽  
Wes Feedback ◽  
Radiative Feedbacks

AbstractThe Tropical Rain belts with an Annual cycle and Continent Model Intercomparison Project (TRACMIP) ensemble includes slab-ocean aquaplanet controls and experiments with a highly idealized tropical continent: modified aquaplanet grid cells with increased evaporative resistance, increased albedo, reduced heat capacity, and no ocean heat transport (zero Q-flux). In the annual mean, an equatorial cold tongue develops west of the continent and induces dry anomalies and a split in the oceanic ITCZ. Ocean cooling is initiated by advection of cold, dry air from the winter portion of the continent; warm, humid anomalies in the summer portion are restricted to the continent by anomalous surface convergence. The surface energy budget suggests that ocean cooling persists and intensifies because of a positive feedback between a colder surface, drier and colder air, reduced downwelling long wave (LW) flux, and enhanced net surface LW cooling (LW feedback). A feedback between wind, evaporation, and SST (WES feedback) also contributes to the establishment and maintenance of the cold tongue. Simulations with a grayradiation model and simulations that diverge from protocol (with negligible winter cooling) confirm the importance of moist-radiative feedbacks and of rectification effects on the seasonal cycle. This mechanism coupling the continental and oceanic climate might be relevant to the double ITCZ bias. The key role of the LW feedback suggests that the study of interactions between monsoons and oceanic ITCZs requires full-physics models and a hierarchy of land models that considers evaporative processes alongside heat capacity as a defining characteristic of land.

scholarly journals Tropical Biases in CMIP5 Multimodel Ensemble: The Excessive Equatorial Pacific Cold Tongue and Double ITCZ Problems*

2014 ◽  
Vol 27 (4) ◽  
pp. 1765-1780 ◽  
Author(s):  
Gen Li ◽  
Shang-Ping Xie
Keyword(s):  
General Circulation ◽  
General Circulation Models ◽  
Atmospheric Model ◽  
Equatorial Pacific ◽  
Cold Tongue ◽  
Model Intercomparison ◽  
Tropical Ocean ◽  
Easterly Wind ◽  
Double Itcz ◽  
Intercomparison Project

Abstract Errors of coupled general circulation models (CGCMs) limit their utility for climate prediction and projection. Origins of and feedback for tropical biases are investigated in the historical climate simulations of 18 CGCMs from phase 5 of the Coupled Model Intercomparison Project (CMIP5), together with the available Atmospheric Model Intercomparison Project (AMIP) simulations. Based on an intermodel empirical orthogonal function (EOF) analysis of tropical Pacific precipitation, the excessive equatorial Pacific cold tongue and double intertropical convergence zone (ITCZ) stand out as the most prominent errors of the current generation of CGCMs. The comparison of CMIP–AMIP pairs enables us to identify whether a given type of errors originates from atmospheric models. The equatorial Pacific cold tongue bias is associated with deficient precipitation and surface easterly wind biases in the western half of the basin in CGCMs, but these errors are absent in atmosphere-only models, indicating that the errors arise from the interaction with the ocean via Bjerknes feedback. For the double ITCZ problem, excessive precipitation south of the equator correlates well with excessive downward solar radiation in the Southern Hemisphere (SH) midlatitudes, an error traced back to atmospheric model simulations of cloud during austral spring and summer. This extratropical forcing of the ITCZ displacements is mediated by tropical ocean–atmosphere interaction and is consistent with recent studies of ocean–atmospheric energy transport balance.

scholarly journals Contrasting Cloud Radiative Feedbacks during Warm Pool and Cold Tongue El Niños

SOLA ◽  
2018 ◽  
Vol 14 (0) ◽  
pp. 126-131 ◽  
Author(s):  
Lin Chen ◽  
Lu Wang ◽  
Tim Li ◽  
De-Zheng Sun
Keyword(s):  
Warm Pool ◽  
Cold Tongue ◽  
Radiative Feedbacks

The Double-ITCZ Bias in CMIP6 Models

2020 ◽  
Author(s):  
Baijun Tian
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Coupled Model ◽  
Global Climate Models ◽  
Cmip5 Models ◽  
Tropical Precipitation ◽  
Double Itcz ◽  
Intercomparison Project ◽  
Fully Coupled

<p>The double-Intertropical Convergence Zone (ITCZ) bias is one of the most outstanding problems in climate models. This study seeks to examine the double-ITCZ bias in the latest state-of-the-art fully coupled global climate models that participated in Coupled Model Intercomparison Project (CMIP) Phase 6 (CMIP6) in comparison to their previous generations (CMIP3 and CMIP5 models). To that end, we have analyzed the long-term annual mean tropical precipitation distributions and several precipitation bias indices that quantify the double-ITCZ biases in 75 climate models including 24 CMIP3 models, 25 CMIP3 models, and 26 CMIP6 models. We find that the double-ITCZ bias and its big inter-model spread persist in CMIP6 models but the double-ITCZ bias is slightly reduced from CMIP3 or CMIP5 models to CMIP6 models.</p>

scholarly journals Cloud and Water Vapor Feedbacks to the El Niño Warming: Are They Still Biased in CMIP5 Models?

2013 ◽  
Vol 26 (14) ◽  
pp. 4947-4961 ◽  
Author(s):  
Lin Chen ◽  
Yongqiang Yu ◽  
De-Zheng Sun
Keyword(s):  
Water Vapor ◽  
El Niño ◽  
Radiative Forcing ◽  
Large Scale ◽  
El Nino ◽  
Coupled Model ◽  
Cmip5 Models ◽  
Cold Tongue ◽  
Key Factor ◽  
Intercomparison Project

Abstract Previous evaluations of model simulations of the cloud and water vapor feedbacks in response to El Niño warming have singled out two common biases in models from phase 3 of the Coupled Model Intercomparison Project (CMIP3): an underestimate of the negative feedback from the shortwave cloud radiative forcing (SWCRF) and an overestimate of the positive feedback from the greenhouse effect of water vapor. Here, the authors check whether these two biases are alleviated in the CMIP5 models. While encouraging improvements are found, particularly in the simulation of the negative SWCRF feedback, the biases in the simulation of these two feedbacks remain prevalent and significant. It is shown that bias in the SWCRF feedback correlates well with biases in the corresponding feedbacks from precipitation, large-scale circulation, and longwave radiative forcing of clouds (LWCRF). By dividing CMIP5 models into two categories—high score models (HSM) and low score models (LSM)—based on their individual skills of simulating the SWCRF feedback, the authors further find that ocean–atmosphere coupling generally lowers the score of the simulated feedbacks of water vapor and clouds but that the LSM is more affected by the coupling than the HSM. They also find that the SWCRF feedback is simulated better in the models that have a more realistic zonal extent of the equatorial cold tongue, suggesting that the continuing existence of an excessive cold tongue is a key factor behind the persistence of the feedback biases in models.

scholarly journals Role of Equatorial Cold Tongue in Central Pacific Double-ITCZ Bias in the NCAR CESM1.2

2020 ◽  
Vol 33 (24) ◽  
pp. 10407-10418
Author(s):  
Xiaoliang Song ◽  
Guang Jun Zhang
Keyword(s):  
Lower Troposphere ◽  
Walker Circulation ◽  
Atmospheric Model ◽  
Necessary Condition ◽  
Cold Tongue ◽  
Central Pacific ◽  
Easterly Wind ◽  
Sst Bias ◽  
Double Itcz ◽  
Downwind Side

AbstractWarm SST bias underlying the spurious southern ITCZ has long been recognized as one of the main causes for double-ITCZ bias in coupled GCMs in the central Pacific. This study demonstrates that the NCAR CESM1.2 can still simulate significant double-ITCZ bias even with cold SST bias in the southern ITCZ region, indicating that warm SST bias is not a necessary condition for double-ITCZ bias in the central Pacific. Further analyses suggest that the equatorial cold tongue (ECT) biases play important roles in the formation of double-ITCZ bias in the central Pacific. The severe cold SST biases in the ECT region in the central Pacific may enhance the SST gradient between the ECT and southern ITCZ region, strengthening the lower-troposphere dynamical convergence and hence convection in the southern ITCZ region. The formation mechanism of excessive ECT bias is further investigated. It is shown that the cold SST biases in the ECT region can be largely attributed to the anomalous cooling tendency produced by the upper-ocean zonal advection due to overly strong zonal currents. In the ECT region, the westward ocean surface zonal current is driven by the equatorial easterly surface winds. It is shown that convection bias simulated by the atmospheric model in the equatorial Amazon region may lead to easterly wind bias in the downwind side (west) of convection region. The mean Walker circulation transports these easterly wind momentum anomalies downward and westward to the surface, resulting in the overly strong surface easterly wind in the central equatorial Pacific.

scholarly journals The Eastern Pacific ITCZ during the Boreal Spring

2005 ◽  
Vol 62 (4) ◽  
pp. 1157-1174 ◽  
Author(s):  
Guojun Gu ◽  
Robert F. Adler ◽  
Adam H. Sobel
Keyword(s):  
Tropical Rainfall Measuring Mission ◽  
Global Precipitation Climatology Project ◽  
Eastern Pacific ◽  
Cold Tongue ◽  
Boreal Spring ◽  
Double Itcz ◽  
The Difference ◽  
Spatial Locations ◽  
Global Precipitation ◽  
North And South

Abstract The 6-yr (1998–2003) rainfall products from the Tropical Rainfall Measuring Mission (TRMM) are used to quantify the intertropical convergence zone (ITCZ) in the eastern Pacific (defined by longitudinal averages over 90°–130°W) during boreal spring (March–April). The double-ITCZ phenomenon, represented by the occurrence of two maxima with respect to latitude in monthly mean rainfall, is observed in most but not all of the years studied. The relative spatial locations of maxima in sea surface temperature (SST), rainfall, and surface pressure are examined. Interannual and weekly variability are characterized in SST, rainfall, surface convergence, total column water vapor, and cloud water. There appears to be a competition for rainfall between the two hemispheres during this season. When one of the two rainfall maxima is particularly strong, the other tends to be weak, with the total rainfall integrated over the two varying less than does the difference between the rainfall integrated over each separately. There is some evidence for a similar competition between the SST maxima in the two hemispheres, but this is more ambiguous, and there is evidence that some variations in the relative strengths of the two rainfall maxima may be independent of SST. Using a 25-yr (1979–2003) monthly rainfall dataset from the Global Precipitation Climatology Project (GPCP), four distinct ITCZ types during March–April are defined, based on the relative strengths of rainfall peaks north and south of, and right over, the equator. Composite meridional profiles and spatial distributions of rainfall and SST are documented for each type. Consistent with previous studies, an equatorial cold tongue is essential to the existence of the double ITCZs. However, too strong a cold tongue may dampen either the southern or northern rainfall maximum, depending on the magnitude of SST north of the equator.

scholarly journals The Variability of Air-sea O2 Flux in CMIP6: Implications for Estimating Terrestrial and Oceanic Carbon Sinks

2022 ◽  
Author(s):  
Changyu Li ◽  
Jianping Huang ◽  
Lei Ding ◽  
Yu Ren ◽  
Linli An ◽  
...  
Keyword(s):  
Decadal Variability ◽  
Coupled Model ◽  
Carbon Uptake ◽  
Oxygen Budget ◽  
Oceanic Climate ◽  
Intercomparison Project ◽  
Carbon Project ◽  
Oceanic Carbon ◽  
Year 2000 ◽  
Global Carbon

AbstractThe measurement of atmospheric O2 concentrations and related oxygen budget have been used to estimate terrestrial and oceanic carbon uptake. However, a discrepancy remains in assessments of O2 exchange between ocean and atmosphere (i.e. air-sea O2 flux), which is one of the major contributors to uncertainties in the O2-based estimations of the carbon uptake. Here, we explore the variability of air-sea O2 flux with the use of outputs from Coupled Model Intercomparison Project phase 6 (CMIP6). The simulated air-sea O2 flux exhibits an obvious warming-induced upward trend (∼1.49 Tmol yr−2) since the mid-1980s, accompanied by a strong decadal variability dominated by oceanic climate modes. We subsequently revise the O2-based carbon uptakes in response to this changing air-sea O2 flux. Our results show that, for the 1990–2000 period, the averaged net ocean and land sinks are 2.10±0.43 and 1.14±0.52 GtC yr−1 respectively, overall consistent with estimates derived by the Global Carbon Project (GCP). An enhanced carbon uptake is found in both land and ocean after year 2000, reflecting the modification of carbon cycle under human activities. Results derived from CMIP5 simulations also investigated in the study allow for comparisons from which we can see the vital importance of oxygen dataset on carbon uptake estimations.

scholarly journals Retrieval of Model Grid-Scale Heat Capacity Using Geostationary Satellite Products. Part I: First Case-Study Application

2005 ◽  
Vol 44 (9) ◽  
pp. 1346-1360 ◽  
Author(s):  
Richard T. McNider ◽  
William M. Lapenta ◽  
Arastoo P. Biazar ◽  
Gary J. Jedlovec ◽  
Ronnie J. Suggs ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Capacity ◽  
General Circulation ◽  
Mesoscale Model ◽  
Regional Scale ◽  
Model Performance ◽  
General Circulation Models ◽  
Surface Energy Budget ◽  
Scale Model ◽  
First Case

Abstract In weather forecast and general circulation models the behavior of the atmospheric boundary layer, especially the nocturnal boundary layer, can be critically dependent on the magnitude of the effective model grid-scale bulk heat capacity. Yet, this model parameter is uncertain both in its value and in its conceptual meaning for a model grid in heterogeneous conditions. Current methods for estimating the grid-scale heat capacity involve the areal/volume weighting of heat capacity (resistance) of various, often ill-defined, components. This can lead to errors in model performance in certain parameter spaces. Here, a technique is proposed and tested for recovering bulk heat capacity using time tendencies in satellite-retrieved surface skin temperature (SST). The technique builds upon sensitivity studies that show that surface temperature is most sensitive to thermal inertia in the early evening hours. The retrievals are made within the context of a surface energy budget in a regional-scale model [the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5)]. The retrieved heat capacities are used in the forecast model, and it is shown that the model predictions of temperature are improved in the nighttime during the forecast periods.

scholarly journals Separating the Impact of Individual Land Surface Properties on the Terrestrial Surface Energy Budget in both the Coupled and Uncoupled Land–Atmosphere System

2019 ◽  
Vol 32 (18) ◽  
pp. 5725-5744 ◽  
Author(s):  
Marysa M. Laguë ◽  
Gordon B. Bonan ◽  
Abigail L. S. Swann
Keyword(s):  
Surface Energy ◽  
Surface Temperature ◽  
Surface Properties ◽  
Energy Budget ◽  
Land Surface ◽  
Temperature Response ◽  
Surface Energy Budget ◽  
Evaporative Resistance ◽  
Atmospheric Feedbacks ◽  
The Impact

Abstract Changes in the land surface can drive large responses in the atmosphere on local, regional, and global scales. Surface properties control the partitioning of energy within the surface energy budget to fluxes of shortwave and longwave radiation, sensible and latent heat, and ground heat storage. Changes in surface energy fluxes can impact the atmosphere across scales through changes in temperature, cloud cover, and large-scale atmospheric circulation. We test the sensitivity of the atmosphere to global changes in three land surface properties: albedo, evaporative resistance, and surface roughness. We show the impact of changing these surface properties differs drastically between simulations run with an offline land model, compared to coupled land–atmosphere simulations that allow for atmospheric feedbacks associated with land–atmosphere coupling. Atmospheric feedbacks play a critical role in defining the temperature response to changes in albedo and evaporative resistance, particularly in the extratropics. More than 50% of the surface temperature response to changing albedo comes from atmospheric feedbacks in over 80% of land areas. In some regions, cloud feedbacks in response to increased evaporative resistance result in nearly 1 K of additional surface warming. In contrast, the magnitude of surface temperature responses to changes in vegetation height are comparable between offline and coupled simulations. We improve our fundamental understanding of how and why changes in vegetation cover drive responses in the atmosphere, and develop understanding of the role of individual land surface properties in controlling climate across spatial scales—critical to understanding the effects of land-use change on Earth’s climate.

High Cloud Responses to Global Warming Simulated by Two Different Cloud Microphysics Schemes Implemented in the Nonhydrostatic Icosahedral Atmospheric Model (NICAM)

2016 ◽  
Vol 29 (16) ◽  
pp. 5949-5964 ◽  
Author(s):  
Ying-Wen Chen ◽  
Tatsuya Seiki ◽  
Chihiro Kodama ◽  
Masaki Satoh ◽  
Akira T. Noda ◽  
...  
Keyword(s):  
Global Warming ◽  
Radiative Forcing ◽  
Atmospheric Model ◽  
Cloud Microphysics ◽  
Cloud Fraction ◽  
Cirrus Clouds ◽  
Boreal Summer ◽  
Model Intercomparison ◽  
Intercomparison Project ◽  
Radiative Feedbacks

Abstract This study examines cloud responses to global warming using a global nonhydrostatic model with two different cloud microphysics schemes. The cloud microphysics schemes tested here are the single- and double-moment schemes with six water categories: these schemes are referred to as NSW6 and NDW6, respectively. Simulations of one year for NSW6 and one boreal summer for NDW6 are performed using the nonhydrostatic icosahedral atmospheric model with a mesh size of approximately 14 km. NSW6 and NDW6 exhibit similar changes in the visible cloud fraction under conditions of global warming. The longwave (LW) cloud radiative feedbacks in NSW6 and NDW6 are within the upper half of the phase 5 of the Coupled Model Intercomparison Project (CMIP5)–Cloud Feedback Model Intercomparison Project 2 (CFMIP2) range. The LW cloud radiative feedbacks are mainly attributed to cirrus clouds, which prevail more in the tropics under global warming conditions. For NDW6, the LW cloud radiative feedbacks from cirrus clouds also extend to midlatitudes. The changes in cirrus clouds and their effects on LW cloud radiative forcing (LWCRF) are assessed based on changes in the effective radii of ice hydrometeors () and the cloud fraction. It was determined that an increase in has a nonnegligible impact on LWCRF compared with an increase in cloud fraction.

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