Alleviating tropical Atlantic sector biases in the Kiel climate model by enhancing horizontal and vertical atmosphere model resolution: climatology and interannual variability

Harlaß, Jan; Latif, Mojib; Park, Wonsun

doi:10.1007/s00382-017-3760-4

Cited by 50 publications

(50 citation statements)

References 76 publications

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“…During this period, wind stress curl is at its maximum while alongshore wind stress is weak, coinciding with an offshore displacement of the zero‐wind stress curl contour. These results underline the importance of the precise cross‐shore wind structure for correctly simulating the EBC in upwelling regions that has been suggested previously (Fennel et al, ; Harlaß et al, , ; Junker et al, ; McCreary & Chao, ; Patricola & Chang, ; Small et al, ). Underneath the MC in the lCW layer, average flow was equatorward during both seasons.…”

Section: Resultssupporting

confidence: 81%

Seasonal Variability of the Mauritania Current and Hydrography at 18°N

2018

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Extensive field campaigns in the Mauritanian upwelling region between 2005 and 2016 provide the database for analyzing the seasonal variability of the eastern boundary circulation (EBC) and associated water mass distribution at 18°N. The data set includes shipboard upper ocean current, hydrographic, and oxygen measurements from nine research cruises conducted during upwelling (December to April) and relaxation (May to July) seasons. During the upwelling season, the EBC closely resembles a classical eastern boundary current regime, with a poleward undercurrent flowing beneath an equatorward coastal jet. In contrast, elevated poleward flow exceeding 30 cm/s and extending from the surface down to 250‐m depth is observed during the relaxation season. The pronounced seasonal variability of the across‐shore structure of the EBC can be related to local wind forcing and is in general agreement with Sverdrup balance. The EBC transport is correlated to the wind stress curl leading the transport by 7 days. The short lead time suggests a fast response of locally forced waves adjusting the EBC to wind forcing. The seasonal and vertical water mass distribution is presented based on hydrographic observations. The meridional oxygen distribution and corresponding water mass partitioning into South and North Atlantic Central Water masses reveal a possible northerly ventilation pathway in the deeper layers of the central water stratum. Our results suggest that the poleward surface flow and the poleward undercurrent both are a consequence of the cyclonic wind stress curl forcing and thus propose to name it the Mauritania Current.

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Section: Resultssupporting

confidence: 81%

Seasonal Variability of the Mauritania Current and Hydrography at 18°N

2018

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“…These results also suggest that reducing the Atlantic SST bias across coupled models should still be a priority for model developers, as it is difficult to make assessments of the likelihood of future wetting or drying while these biases persist. Recent work by Harlaß et al () has found that increased horizontal and vertical model resolution contributes to improvements in model representation of the tropical Atlantic climatology. Improving resolution may therefore be an important element of reducing this bias in future generations of coupled models.…”

Section: Discussion and Summarymentioning

confidence: 99%

“…Recent work by Harlaß et al (2018) has found that increased horizontal and vertical model resolution contributes to improvements in model representation of the tropical Atlantic climatology. Improving resolution may therefore be an important element of reducing this bias in future generations of coupled models.…”

Section: 1029/2018jd029847mentioning

confidence: 99%

The Plausibility of September–November Congo Basin Rainfall Change in Coupled Climate Models

2019

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As one of three global hot spots of tropical convection, potential future changes to the Congo Basin climate system will have regional and tropics‐wide implications. However, the latest generation of climate models from the Coupled Model Intercomparison Project 5 disagree on the sign and magnitude of future change and diverge in their estimation of the historical rainfall climatology. This study assesses the plausibility of different signals of future rainfall change by examining the processes relating to rainfall projections in samples of historically wet or dry models during the September–November rainy season. In the west Congo Basin, there are no significant differences in rainfall change projections in models that are historically wet or dry. Both composites feature wetting in the north (up to 1.8 mm/day) and drying in the south, associated with enhanced tropical Atlantic sea surface temperatures, increased evaporation, and enhanced low‐level moisture flux into the basin. In the east Congo Basin, there is greater evidence that differences in model historical climatologies has an influence on the magnitude of future rainfall change. Historically wet models project significant wetting in the northeast (1.19 mm/day) associated with a weakened northern component of the African Easterly Jet (AEJ) and enhanced moisture convergence. Dry models do not capture the structure of the AEJs in the historical period, and so changes to the AEJs under warming do not produce the same wetting pattern. The analysis therefore casts doubt on the plausibility of the driest rainfall change signals in the east Congo Basin.

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“…Further, Harlaß el al. [10] pointed out that higher resolution of the atmospheric component in the CCM is also crucial for reducing the warm SST bias over the ACT region. In the future, a high-resolution ocean model should be used to quantify the role of atmospheric variable biases in inducing SST biases over the ACT region.…”

Section: Discussionmentioning

confidence: 99%

“…In the southeastern tropical Atlantic (SETA) region (25 • S-10 • S, 10 • W-15 • E), the warm SST bias is mainly concentrated in the Angola-Benguela Frontal Zone [3,[6][7][8][9][10][11][12] (ABFZ) with a magnitude that exceeds 5 • C (IPCC 2013). The origins of the warm bias over the ABFZ have already been attributed to both local sources [4,5,[9][10][11] and remote sources [4,13]. Local sources include underestimated low-level winds [1,11,[14][15][16][17][18] and insufficient stratocumulus cloud cover [19][20][21].…”

Section: Introductionmentioning

confidence: 99%

Origin of Warm SST Bias over the Atlantic Cold Tongue in the Coupled Climate Model FGOALS-g2

et al. 2018

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Abstract:Most of the coupled models contain a strong warm bias in sea surface temperature (SST) over the Atlantic Cold Tongue (ACT) region (10 • S-3 • N, 20 • W-10 • E) during June-August (JJA) and September-November (SON). In this study, the origins of the ACT SST bias and their relative contributions to the bias are explored by conducting a set of sensitivity experiments, which are based on an ocean-ice model, and by ignoring the nonlinear effects of each origin. The origins for the warm bias over the ACT in the coupled climate model during JJA are estimated as follows: westerly wind bias along the equator (5 • S-5 • N) during March-May (MAM; contributes approximately 32.6% of the warm bias), northerly bias over the southern tropical Atlantic (25 • S-3 • N, 40 • W-20 • E) during MAM and JJA (21.4%), bias in the surface specific humidity and surface air temperature (11.9%), and downward shortwave radiation bias (6.5%). The origins of the ACT bias during SON are as follows: northerly bias over the southern tropical Atlantic during SON (31.2%), bias in the surface specific humidity and surface air temperature (27.9%), downward shortwave radiation bias (17.4%), and zonal wind bias (13.4%). Note that these contribution ratios of these origins may be model-dependent. In addition, the local and non-local effects of the zonal wind bias are explored explicitly, while those of all the other biases are examined implicitly. Therefore, a better-performing atmospheric component is crucial when simulating zonal winds during MAM along the equator (5 • S-5 • N) and meridional winds during MAM, JJA, and SON over the southern tropical Atlantic, which will alleviate the warm bias over the ACT region in the coupled climate model.

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Alleviating tropical Atlantic sector biases in the Kiel climate model by enhancing horizontal and vertical atmosphere model resolution: climatology and interannual variability

Cited by 50 publications

References 76 publications

Seasonal Variability of the Mauritania Current and Hydrography at 18°N

Seasonal Variability of the Mauritania Current and Hydrography at 18°N

The Plausibility of September–November Congo Basin Rainfall Change in Coupled Climate Models

Origin of Warm SST Bias over the Atlantic Cold Tongue in the Coupled Climate Model FGOALS-g2

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