scholarly journals Biases in the Atlantic ITCZ in Seasonal–Interannual Variations for a Coarse- and a High-Resolution Coupled Climate Model

2012 ◽  
Vol 25 (16) ◽  
pp. 5494-5511 ◽  
Author(s):  
Takeshi Doi ◽  
Gabriel A. Vecchi ◽  
Anthony J. Rosati ◽  
Thomas L. Delworth
Keyword(s):  
High Resolution ◽  
South America ◽  
Climate Model ◽  
Coupled Processes ◽  
Boreal Summer ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Tropical Atlantic ◽  
Model Version ◽  
Northern South America ◽  
Atlantic Itcz

Abstract Using two fully coupled ocean–atmosphere models—Climate Model version 2.1 (CM2.1), developed at the Geophysical Fluid Dynamics Laboratory, and Climate Model version 2.5 (CM2.5), a new high-resolution climate model based on CM2.1—the characteristics and sources of SST and precipitation biases associated with the Atlantic ITCZ have been investigated. CM2.5 has an improved simulation of the annual mean and the annual cycle of the rainfall over the Sahel and northern South America, while CM2.1 shows excessive Sahel rainfall and lack of northern South America rainfall in boreal summer. This marked improvement in CM2.5 is due to not only high-resolved orography but also a significant reduction of biases in the seasonal meridional migration of the ITCZ. In particular, the seasonal northward migration of the ITCZ in boreal summer is coupled to the seasonal variation of SST and a subsurface doming of the thermocline in the northeastern tropical Atlantic, known as the Guinea Dome. Improvements in the ITCZ allow for better representation of the coupled processes that are important for an abrupt seasonally phase-locked decay of the interannual SST anomaly in the northern tropical Atlantic. Nevertheless, the differences between CM2.5 and CM2.1 were not sufficient to reduce the warm SST biases in the eastern equatorial region and Angola–Benguela area. The weak bias of southerly winds along the southwestern African coast associated with the excessive southward migration bias of the ITCZ may be a key to improve the warm SST biases there.

scholarly journals Weaker AMOC in coupled models inhibits north tropical Atlantic impact on ENSO

2020 ◽  
Author(s):  
Belen Rodriguez-Fonseca ◽  
Irene Polo ◽  
Elsa Mohino ◽  
Teresa Losada ◽  
Marta Martín-Rey ◽  
...  
Keyword(s):  
Climate Model ◽  
Boreal Summer ◽  
Tropical Atlantic ◽  
Coupled Models ◽  
Tropical North Atlantic ◽  
Different Seasons ◽  
Climate Model Simulations ◽  
Open Question ◽  
First Time ◽  
Atlantic Itcz

<p align="justify"><span>Observational studies have reported that interannual variability of sea surface temperature in two tropical Atlantic regions can act as ENSO predictors in different seasons and periods: boreal summer Atlantic Nino (AN) in negative phases of the Atlantic Multidecadal Variabil- ˜ ity (AMV); and boreal spring tropical north Atlantic (TNA) in positive AMV. The robustness of the AMV role in the interbasin connection remains an open question due to the short observational record. Using observations and pre-industrial climate model simulations, we demonstrate for the first time that latitudinal displacements of the Atlantic ITCZ act as a switch for the type of inter-basin teleconnection. During periods in which the Atlantic ITCZ is further equatorward (northward) AN (TNA) impacts ENSO. This ITCZ location can be 1 affected by several factors, including the inter-hemispheric SST gradients associated with AMV.Coupled models success in capturing the AN-ENSO connection. Nevertheless, they have difficulties in reproducing the TNA-ENSO connection because they overestimate rainfall in the southern tropical Atlantic. The TNA-ENSO connection occurs sporadically during periods when the ITCZ is shifted further northward in association with strong heat transports by the AMOC. Weaker AMOC periods in coupled models don't present the TNA-ENSO connection. State-of-the-art models still need to improve for correctly representing tropical Atlantic impact on ENSO.</span></p>

scholarly journals South American Climate during the Early Eocene: Impact of a Narrower Atlantic and Higher Atmospheric CO2

2020 ◽  
Vol 33 (2) ◽  
pp. 691-706 ◽  
Author(s):  
Xiaojuan Liu ◽  
David S. Battisti ◽  
Rachel H. White ◽  
Paul A. Baker
Keyword(s):  
South America ◽  
Climate Model ◽  
Atmospheric Composition ◽  
South American ◽  
Early Eocene ◽  
Tropical Atlantic ◽  
State Changes ◽  
Climate Model Simulations ◽  
South American Climate ◽  
Tropical South America

AbstractThe Cenozoic climate of tropical South America was fundamental to the development of its biota, the most biodiverse on Earth. No previous studies have explicitly addressed how the very different atmospheric composition and Atlantic geometry during the early Eocene (approximately 55 million years ago) may have affected South American climate. At that time, the Atlantic Ocean was approximately half of its current width and the CO2 concentration of Earth’s atmosphere ranged from ~550 to ~1500 ppm or even higher. Climate model simulations were performed to examine the effects of these major state changes on the climate of tropical South America. Reducing the width of the Atlantic by approximately half produces significant drying relative to modern climate. Drying is only partly offset by an enhancement of precipitation due to the higher CO2 of the early Eocene. The main mechanism for drier conditions is simple. Low-level air crosses the tropical Atlantic from North Africa in much less time for a narrower Atlantic (2 days) than for the modern Atlantic (~6 days); as a result, much less water is evaporated into the air and thus there is far lower moisture imported to the continent in the Eocene simulation than in the modern control. The progressive wetting (during the mid- to late Cenozoic) of the Amazon due to the widening Atlantic and the rising Andes, only partly offset by decreasing CO2 values, may have been partly responsible for the accumulating biodiversity of this region.

scholarly journals Modelling the climate and surface mass balance of polar ice sheets using RACMO2, part 2: Antarctica (1979–2016)

2017 ◽  
Author(s):  
Jan Melchior van Wessem ◽  
Willem Jan van de Berg ◽  
Brice P. Y. Noël ◽  
Erik van Meijgaard ◽  
Gerit Birnbaum ◽  
...  
Keyword(s):  
High Resolution ◽  
Mass Balance ◽  
Climate Model ◽  
Ice Sheet ◽  
Climate Scenario ◽  
Surface Mass Balance ◽  
Near Surface ◽  
Surface Mass ◽  
Model Version ◽  
Surface Climate

Abstract. We evaluate modelled Antarctic ice sheet (AIS) near-surface climate, surface mass balance (SMB) and surface energy balance (SEB) from the updated polar version of the regional atmospheric climate model RACMO2 (1979–2016). The updated model, referred to as RACMO2.3p2, incorporates upper-air relaxation, a revised topography, tuned parameters in the cloud scheme to generate more precipitation towards the AIS interior, and modified snow properties reducing drifting snow sublimation and increasing surface snowmelt. Comparisons of RACMO2 model output with several independent observational data show that the existing biases in AIS temperature, radiative fluxes and SMB components are further reduced with respect to the previous model version. The model integrated annual average SMB for the ice sheet including ice shelves (minus the Antarctic Peninsula (AP)) now amounts to 2229 Gt y-1, with an interannual variability of 109 Gt y-1. The largest improvement is found in modelled surface snowmelt, that now compares well with satellite and weather station observations. For the high-resolution (~ 5.5 km) AP simulation, results remain comparable to earlier studies. The updated model provides a new, high-resolution dataset of the contemporary near-surface climate and SMB of the AIS; this model version will be used for future climate scenario projections in a forthcoming study.

Response to CO2 Doubling of the Atlantic Hurricane Main Development Region in a High-Resolution Climate Model

2013 ◽  
Vol 26 (12) ◽  
pp. 4322-4334 ◽  
Author(s):  
Takeshi Doi ◽  
Gabriel A. Vecchi ◽  
Anthony J. Rosati ◽  
Thomas L. Delworth
Keyword(s):  
High Resolution ◽  
Positive Feedback ◽  
Climate Model ◽  
Northern Region ◽  
Early Summer ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Interannual Variations ◽  
Atlantic Hurricane ◽  
Main Development ◽  
Development Region

Abstract Response of climate conditions in the Atlantic hurricane main development region (MDR) to doubling of atmospheric CO2 has been explored using the new high-resolution coupled climate model, version 2.5 (CM2.5), developed at the Geophysical Fluid Dynamics Laboratory (GFDL). In the annual mean, the SST in the MDR warms by about 2°C in the CO2 doubling run relative to the control run; the trade winds become weaker in the northern tropical Atlantic and the rainfall increases over the ITCZ and its northern region. The amplitude of the annual cycle of the SST over the MDR is not significantly changed by CO2 doubling. However, the authors find that the interannual variations show significant responses to CO2 doubling; the seasonal maximum peak of the interannual variations of the SST over the MDR is about 25% stronger than in the control run. The enhancement of the interannual variations of the SST in the MDR is caused by changes in effectiveness of the wind–evaporation–SST (WES) positive feedback; WES remains a positive feedback until boreal early summer in the CO2 doubling run. The enhancement of the interannual variability of the SST over the MDR in boreal early summer due to CO2 doubling could lead to serious damages associated with the Atlantic hurricane count and drought (or flood) in the Sahel and South America in a future climate.

Weakened impact of the Atlantic Niño on the future Guinean coast rainfall

2021 ◽  
Author(s):  
Koffi Worou ◽  
Hugues Goosse ◽  
Thierry Fichefet
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Rainfall Variability ◽  
Coupled Model ◽  
Sea Surface ◽  
Boreal Summer ◽  
Tropical Atlantic ◽  
Equatorial Atlantic ◽  
Sea Level Pressure ◽  
Guinean Coast

<p>Much of the rainfall variability in the Guinean coast area during the boreal summer is driven by the sea surface temperature (SST) variations in the eastern equatorial Atlantic, amplified by land-atmosphere interactions. This oceanic region corresponds to the center of action of the Atlantic Equatorial mode, also termed Atlantic Niño (ATL3), which is the leading SST mode of variability in the tropical Atlantic basin. In years of positive ATL3, above normal SST conditions in the ATL3 area weaken the sea level pressure gradient between the West African lands and the ocean, which in turn reduces the monsoon flow penetration into Sahel. Subsequently, the rainfall increases over the Guinean coast area. According to observations and climate models, the relation between the Atlantic Niño and the rainfall in coastal Guinea is stationary over the 20<sup>th</sup> century. While this relation remains unchanged over the 21<sup>st</sup> century in climate model projections, the strength of the teleconnection is reduced in a warmer climate. The weakened ATL3 effect on the rainfall over the tropical Atlantic (in years of positive ATL3) has been attributed to the stabilization of the atmosphere column above the tropical Atlantic. Analysis of historical and high anthropogenic emission scenario (the Shared Socioeconomic Pathways 5-8.5) simulations from 31 models participating in the sixth phase of the Coupled Model Intercomparison Project suggests an additional role of the Bjerkness feedback. A weakened SST amplitude related to ATL3 positive phases reduces the anomalous westerlies, which in turn increases the upwelling cooling effect on the sea surface. Both the Guinean coast region and the equatorial Atlantic experiment the projected rainfall reduction associated with ATL3, with a higher confidence over the ocean than over the coastal lands.</p>

EXPLORING INLAND TROPICAL CYCLONE RAINFALL AND TORNADOES UNDER FUTURE CLIMATE CONDITIONS THROUGH A CASE STUDY OF HURRICANE IVAN

2020 ◽  
Author(s):  
Dereka Carroll-Smith ◽  
Robert J. Trapp ◽  
James M. Done
Keyword(s):  
Climate Change ◽  
Tropical Cyclone ◽  
Climate Models ◽  
Climate Model ◽  
Convective Available Potential Energy ◽  
Track Length ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Climate System Model ◽  
Hurricane Ivan ◽  
Model Version

AbstractThe overarching purpose of this study is to investigate the impacts of anthropogenic climate change both on the rainfall and tornadoes associated with tropical cyclones (TCs) making landfall in the U.S. Atlantic Basin. The “pseudo-global” warming (PGW) approach is applied to Hurricane Ivan (2004), a historically prolific tropical cyclone tornado (TCT)-producing storm. Hurricane Ivan is simulated under its current climate forcings using the Weather Research and Forecasting model. This control simulation (CTRL) is then compared to PGW simulations in which the current forcings are modified by climate-change differences obtained from the Community Climate System Model version 4 (NCAR), Model for Interdisciplinary Research on Climate version 5 (MIROC), and Geophysical Fluid Dynamics Laboratory Climate Model version 3 (GFDL) climate models. Changes in TC intensity, TC rainfall, and TCT production, identified for the PGW-modified Ivan are documented and analyzed.Compared to CTRL, all three PGW simulations show an increase in TC intensity and generate substantially more accumulated rainfall over the course of Ivan’s progression overland. However, only one of the TCs under PGW (MIROC) produced more TCTs than the control. Evidence is provided that in addition to favorable environmental conditions, TCT production is related to the TC track length and to the strength of the interaction between the TC and an environmental mid-level trough. Enhanced TCT generation at landfall for MIROC and GFDL is attributed to increased values of convective available potential energy, low level shear and storm relative environmental helicity.

scholarly journals Technical Note: The effect of sensor resolution on the number of cloud-free observations from space

2007 ◽  
Vol 7 (11) ◽  
pp. 2881-2891 ◽  
Author(s):  
J. M. Krijger ◽  
M. van Weele ◽  
I. Aben ◽  
R. Frey
Keyword(s):  
High Resolution ◽  
South America ◽  
Technical Note ◽  
Atmospheric Composition ◽  
Focal Points ◽  
Surface Emission ◽  
Sensor Resolution ◽  
Northern South America ◽  
Footprint Area ◽  
Cloud Mask

Abstract. Air quality and surface emission inversions are likely to be focal points for future satellite missions on atmospheric composition. Most important for these applications is sensitivity to the atmospheric composition in the lowest few kilometers of the troposphere. Reduced sensitivity by clouds needs to be minimized. In this study we have quantified the increase in number of useful footprints, i.e. footprints which are sufficient cloud-free, as a function of sensor resolution (footprint area). High resolution (1 km×1 km) MODIS TERRA cloud mask observations are aggregated to lower resolutions. Statistics for different thresholds on cloudiness are applied. For each month in 2004 four days of MODIS data are analyzed. Globally the fraction of cloud-free observations drops from 16% at 100 km2 resolution to only 3% at 10 000 km2 if not a single MODIS observation within a footprint is allowed to be cloudy. If up to 5% or 20% of a footprint is allowed to be cloudy, the fraction of cloud-free observations is 9% or 17%, respectively, at 10 000 km2 resolution. The probability of finding cloud-free observations for different sensor resolutions is also quantified as a function of geolocation and season, showing examples over Europe and northern South America (ITCZ).

An investigation of tropical Atlantic bias in a high-resolution coupled regional climate model

2012 ◽  
Vol 39 (9-10) ◽  
pp. 2443-2463 ◽  
Author(s):  
Christina M. Patricola ◽  
Mingkui Li ◽  
Zhao Xu ◽  
Ping Chang ◽  
R. Saravanan ◽  
...  
Keyword(s):  
High Resolution ◽  
Regional Climate Model ◽  
Climate Model ◽  
Regional Climate ◽  
Tropical Atlantic

The Influence of Amazon Rainfall on the Atlantic ITCZ through Convectively Coupled Kelvin Waves

2007 ◽  
Vol 20 (7) ◽  
pp. 1188-1201 ◽  
Author(s):  
Hui Wang ◽  
Rong Fu
Keyword(s):  
South America ◽  
Surface Wind ◽  
Phase Speed ◽  
Kelvin Waves ◽  
Tropical Atlantic ◽  
Kelvin Wave ◽  
Reanalysis Dataset ◽  
Large Variability ◽  
Boreal Spring ◽  
Atlantic Itcz

Abstract Using outgoing longwave radiation (OLR) and Tropical Rainfall Measuring Mission (TRMM) daily rain-rate data, systematic changes in intensity and location of the Atlantic intertropical convergence zone (ITCZ) were detected along the equator during boreal spring. It is found that the changes in convection over the tropical Atlantic may be induced by deep convection in equatorial South America. Lagged regression analyses demonstrate that the anomalies of convection developed over the land propagate eastward across the Atlantic and then into Africa. The eastward-propagating disturbances appear to be convectively coupled Kelvin waves with a period of 6–7.5 days and a phase speed of around 15 m s−1. These waves modulate the intensity and location of the convection in the tropical Atlantic and result in a zonal variation of the Atlantic ITCZ on synoptic time scales. The convectively coupled Kelvin wave has substantial signals in both the lower and upper troposphere. Both a reanalysis dataset and the Quick Scatterometer (QuikSCAT) ocean surface wind are used to characterize the Kelvin wave. This study suggests that synoptic-scale variation of the Atlantic ITCZ may be linked to precipitation anomalies in South America through the convectively coupled Kelvin wave. The results imply that the changes of Amazon convection could contribute to the large variability of the tropical Atlantic ITCZ observed during boreal spring.

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