The impact of horizontal atmospheric resolution in modelling air–sea heat fluxes

Abstract

Climate modes as simulated by global climate models are often found to be considerably weaker than are observed. One possibility is that coarse‐resolution climate models do not capture turbulent air–sea fluxes sufficiently. Ensemble experiments with the same atmospheric configuration of the Met Office Hadley Centre climate model, forced with observed sea‐surface temperatures (SST) and at three different horizontal model resolutions (approximately 130, 60 and 25 km), are used to test the sensitivity of air–sea surface heat and moisture fluxes. We find that, although global mean budgets at the three resolutions are very similar, substantial differences appear in regional air–sea flux patterns. Increased model resolution consistently enhances zonal‐mean air–sea fluxes in the mid–high latitudes while suppressing heat fluxes in the low latitudes and weakening the Hadley Circulation. In the North Atlantic, annual mean surface heat fluxes into the atmosphere along the Gulf Stream/North Atlantic Current and over the sub‐polar gyre can increase by up to 10 W/m2 when atmospheric model resolution increases from 130 to 60 km. In the Pacific, increased model resolution tends to weaken the Walker Circulation with increased heat fluxes from the east but markedly reduced fluxes from the western Pacific, leading to significantly improved precipitation over the tropical western Pacific and the Maritime Continent. Changes in air–sea heat fluxes come about mainly as a result of changed near‐surface ventilation. Generally, increasing resolution strengthens surface winds and reduces specific humidity in the mid–high latitudes while weakening surface winds over the Tropics and subtropics.

Enhanced Turbulent Heat Fluxes Improve Meiyu‐Baiu Simulation in High‐Resolution Atmospheric Models

“…Both the stronger near-surface wind and less near-surface specific humidity contribute to higher ventilation efficiencies and enhanced ocean forcing of the atmosphere along the Kuroshio, resulting in more turbulent latent heat flux in the HRMs. This agrees with Wu et al (2019). For…”

“…In an earlier study (Wu et al, 2019), we have found that latent heat fluxes in tropics are suppressed in higher-resolution AGCMs, especially in the western Pacific. The local decreased latent heat can strengthen the WNPSH.…”

“…Recent studies have shown that simulated air‐sea heat fluxes are sensitive to the horizontal resolution. Air‐sea heat fluxes in the mid‐high latitudes, particularly areas rich in oceanic fronts and boundary currents where the ocean forces the atmosphere (Hewitt et al., 2017), are enhanced when the model horizontal resolution is increased (Wu et al., 2019). Increasing ocean model resolution improves surface fluxes by enhancing air‐sea coupling (SST‐wind stress relationship) and by improving the mean state (Roberts et al., 2016).…”

A Regime-Oriented Approach to Observationally Constraining Extratropical Shortwave Cloud Feedbacks

“…The response of WVP to warming is strongly constrained by Clausius-Clapeyron, but changes in U 10m are a function of changes in extratropical circulation and are less well constrained in GCMs. It is possible more advanced and higher-resolution models will project a different response in cyclone wind speed (Baker et al 2019;Davini et al 2017;Gonzalez et al 2019;Jiaxiang et al 2020;Roberts et al 2020;Wu et al 2019). However, across the GCMs evaluated here moisture changes dominate the change in WCB moisture flux.…”

The Effect of Modeling Strategies on Assessments of Differential Warming Impacts of 0.5°C

“…Another difference that cannot be neglected is the horizontal resolution, which is much higher in HAP-PI-CAM5 (∼25 km) than the coupled runs (∼100 km; Table 1). There is growing evidence of added value of high resolution modeling in simulating the global hydrological cycle as well as precipitation extremes (Prein et al, 2016;Roberts et al, 2018;Van Der Wiel et al, 2016;Vannière et al, 2018;Wu et al, 2019). For extreme precipitation, specifically, heavier extreme precipitation is permitted overall across the globe in higher-resolution simulations (Chen & Dai, 2019;O'Brien et al, 2016;Wehner et al, 2014).…”