Effects of grid spacing on high-frequency precipitation variance in coupled high-resolution global ocean–atmosphere models

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Light, C., Arbic, B., Martin, P., Brodeau, L., Farrar, J., Griffies, S., Kirtman, B., Laurindo, L., Menemenlis, D., Molod, A., Nelson, A., Nyadjro, E., O’Rourke, A., Shriver, J., Siqueira, L., Small, R., & Strobach, E. Effects of grid spacing on high-frequency precipitation variance in coupled high-resolution global ocean–atmosphere models. Climate Dynamics, (2022): 1–27, https://doi.org/10.1007/s00382-022-06257-6.High-frequency precipitation variance is calculated in 12 different free-running (non-data-assimilative) coupled high resolution atmosphere–ocean model simulations, an assimilative coupled atmosphere–ocean weather forecast model, and an assimilative reanalysis. The results are compared with results from satellite estimates of precipitation and rain gauge observations. An analysis of irregular sub-daily fluctuations, which was applied by Covey et al. (Geophys Res Lett 45:12514–12522, 2018. https://doi.org/10.1029/2018GL078926) to satellite products and low-resolution climate models, is applied here to rain gauges and higher-resolution models. In contrast to lower-resolution climate simulations, which Covey et al. (2018) found to be lacking with respect to variance in irregular sub-daily fluctuations, the highest-resolution simulations examined here display an irregular sub-daily fluctuation variance that lies closer to that found in satellite products. Most of the simulations used here cannot be analyzed via the Covey et al. (2018) technique, because they do not output precipitation at sub-daily intervals. Thus the remainder of the paper focuses on frequency power spectral density of precipitation and on cumulative distribution functions over time scales (2–100 days) that are still relatively “high-frequency” in the context of climate modeling. Refined atmospheric or oceanic model grid spacing is generally found to increase high-frequency precipitation variance in simulations, approaching the values derived from observations. Mesoscale-eddy-rich ocean simulations significantly increase precipitation variance only when the atmosphere grid spacing is sufficiently fine (< 0.5°). Despite the improvements noted above, all of the simulations examined here suffer from the “drizzle effect”, in which precipitation is not temporally intermittent to the extent found in observations.Support for CXL’s effort on this project was provided by a Research Experiences for Undergraduates (REU) supplement for National Science Foundation (NSF) grant OCE-1851164 to BKA, which also provided partial support for PEM. In addition, BKA acknowledges NSF grant OCE-1351837, which provided partial support for AKO, Office of Naval Research grant N00014-19-1-2712 and NASA grants NNX17AH55G, which also provided partial support for ADN, and 80NSSC20K1135. JTF’s participation, and the SPURS-II buoy data, were funded by NASA grants 80NSSC18K1494 and NNX15AG20G

Altimetry for the future: Building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ‘‘Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

Altimetry for the future: building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the “Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

Contribution à l'Amélioration de la Fonction de Forçage des Modèles de Circulation Générale Océanique

The present work focuses on improving the atmospheric forcing function used to drive ocean general circulation hindcasts of the last five decades. First, the behavior of the main parameterizations used to estimate surface fluxes that provide surface boundary conditions to OGCMs is studied in detail. The NEMO ocean/sea-ice model is then used at a 2° coarse resolution to validate atmospheric datasets especially designed to drive the DRAKKAR hierarchy of high-resolution models. These new datasets include, over the period 1958-2004, corrected surface atmospheric fields from ERA-40, a modified satellite radiation product from the ISCCP, and precipitation fields merging different global products. Relevant diagnostics tend to confirm that the simulation of several key features of the ocean circulation are significantly improved while driving DRAKKAR models with these new forcing sets.Ce travail de thèse porte sur l'amélioration du forçage atmosphérique utilisé pour réaliser des simulations numériques inter-annuelles globales de l'état physique de l'océan durant les 5 dernières décennies. Après une étude détaillant et comparant le comportementde diverses paramétrisations utilisées pour estimer les flux de surface servant de conditions limites, le modèle de circulation générale de l'océan et des glaces de mer NEMO est utilisé sur sa configuration à 2° de résolution pour valider des jeux de données atmosphériques spécialement destinés au forçage des modèles haute résolution du projet DRAKKAR. Ces jeux de données combinent, sur une période allant de 1958 à 2004, des champs atmosphériques de surface corrigés issus de ERA-40, une recalibration des radiations satellitaires de L'ISCCP ainsi que des précipitations incorporant différents produits globaux. Divers diagnostics confirment que ces nouveaux forçages mènent à une meilleure simulation de certaines caractéristiques clefs de la circulation océanique globale

Contribution à l'Amélioration de la Fonction de Forçage des Modèles de Circulation Générale Océanique

Ce travail de thèse porte sur l'amélioration du forçage atmosphérique utilisé pour réaliser des simulations numériques inter-annuelles globales de l'état physique de l'océan durant les 5 dernières décennies. Après une étude détaillant et comparant le comportement de diverses paramétrisations utilisées pour estimer les flux de surface servant de conditions limites, le modèle de circulation générale de l'océan et des glaces de mer NEMO est utilisé sur sa configuration à 2 de résolution pour valider des jeux de données atmosphériques spécialement destinés au forçage des modèles haute résolution du projet DRAKKAR. Ces jeux de données combinent, sur une période allant de 1958 à 2004, des champs atmosphériques de surface corrigés issus de ERA-40, une recalibration des radiations satellitaires de L'ISCCP ainsi que des précipitations incorporant différents produits globaux. Divers diagnostics confirment que ces nouveaux forçages mènent à une meilleure simulation de certaines caractéristiques clefs de la circulation océanique globale.The present work focuses on improving the atmospheric forcing function used to drive ocean general circulation hindcasts of the last five decades. First, the behavior of the main parameterizations used to estimate surface fluxes that provide surface boundary conditions to OGCMs is studied in detail. The NEMO ocean/sea-ice model is then used at a 2 coarse resolution to validate atmospheric datasets especially designed to drive the DRAKKAR hierarchy of high-resolution models. These new datasets include, over the period 1958-2004, corrected surface atmospheric fields from ERA-40, a modified satellite radiation product from the ISCCP, and precipitation fields merging different global products. Relevant diagnostics tend to confirm that the simulation of several key features of the ocean circulation are significantly improved while driving DRAKKAR models with these new forcing sets.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Extinction of the northern oceanic deep convection in an ensemble of climate model simulations of the 20th and 21st centuries

We study the variability and the evolution of oceanic deep convection in the northern North Atlantic and the Nordic Seas from 1850 to 2100 using an ensemble of 12 climate model simulations with EC-Earth. During the historical period, the model shows a realistic localization of the main sites of deep convection, with the Labrador Sea accounting for most of the deep convective mixing in the northern hemisphere. Labrador convection is partly driven by the NAO (correlation of 0.6) and controls part of the variability of the AMOC at the decadal time scale (correlation of 0.6 when convection leads by 3-4 years). Deep convective activity in the Labrador Sea starts to decline and to become shallower in the beginning of the twentieth century.  The decline is primarily caused by a decrease of the sensible heat loss to the atmosphere in winter resulting from increasingly warm atmospheric conditions. It occurs stepwise and is mainly the consequence of two severe drops in deep convective activity during the 1920s and the 1990s.  These two events can both be linked to the low-frequency variability of the NAO. A warming of the sub-surface, resulting from reduced convective mixing, combines with an increasing influx of freshwater from the Nordic Seas to rapidly strengthen the surface stratification and prevent any possible resurgence of deep convection in the Labrador Sea after the 2020s. Deep convection in the Greenland Sea starts to decline in the 2020s, until complete extinction in 2100. As a response to the extinction of deep convection in the Labrador and Greenland Seas, the AMOC undergoes a linear decline at a rate of about -0.3 Sv per decade during the twenty-first century

News: Ocean surface forcing and surface fields

Exchanges of energy and water occurring at the air-sea interface establish links and feedbacks between the atmosphere and the ocean, and are key processes in the climate and weather systems. There are great needs in climate and oceanographic research for high quality estimates of large scale fluxes of heat, freshwater and momentum. There has been substantial progress in our knowledge of the ocean surface fluxes in recent years. Nevertheless, new challenges have emerged, stimulated by the use of eddy-resolving ocean general circulation models (OGCMs) to investigate the ocean decadal variability and by the rapid development of operational oceanography. The state of our knowledge in the field of air-sea exchanges of energy and water is comprehensively covered in the report on air-sea fluxes from the WCRP working group (1). For in-depth considerations on the need of surface fluxes in operational ocean analysis and forecasting systems, we recommend the book chapter by W. Large (2)

The bulk parameterizations of turbulent air-sea fluxes in NEMO4: the origin of sea surface temperature differences in a global model study

International audienceWind stress and turbulent heat fluxes are the major driving forces that modify the ocean dynamics and thermodynamics. In the Nucleus for European Modelling of the Ocean (NEMO) ocean general circulation model, these turbulent air-sea fluxes (TASFs) can critically impact the simulated ocean characteristics. This paper investigates how the various bulk parameterizations used to calculate turbulent air-sea fluxes in NEMOv4 can lead to substantial differences in the estimation of sea surface temperatures (SSTs). Specifically, we study the contributions of different aspects and assumptions of the bulk parameterizations in driving the SST differences in the NEMO global model configuration at 1/4° of horizontal resolution. These aspects include the use of the skin temperature instead of the bulk SST in the computation of turbulent heat flux components and the estimation of wind stress and turbulent heat flux components, which vary in each parameterization due to different bulk transfer coefficients. The analysis of a set of short-term sensitivity experiments where the only change is related to one of the aspects of the bulk parameterizations shows that parameterization-related SST differences are primarily sensitive to wind stress differences and to the implementation of skin temperature in the computation of turbulent heat flux components. In addition, in order to highlight the role of SST-turbulent heat flux negative feedback at play in ocean simulations, we compare the TASF differences obtained using the NEMO ocean model with the estimations by Brodeau et al. (2017), who compared the different bulk parameterizations using prescribed SSTs. Our estimations of turbulent heat flux differences between bulk parameterizations are weaker than those found by Brodeau et al. (2017)