Abstract

Climatological monthly mean variations of the surface heat fluxes over the East China Sea and the Yellow Sea are calculated by both a data analysis and a numerical simulation. The result of the data analysis based on the empirical/bulk method agrees well with the directly observed solar radiation and several previous studies of the surface heat fluxes. An adjustment in the formation of the Haney-type heat flux is presented by comparing to the result of the bulk method. The numerical simulation of these seas using an ocean general circulation model demonstrates the success of the improved Haney-type condition over the original one in simulating sea surface temperature. The surface heat flux simulated in the Yellow Sea is more reasonable than by the data analysis considering the total heat budget of this sea.

Abstract

In the summer of 2020, South Korea experienced record-breaking rainfall due to 15 consecutive heavy rainfall events (HREs) from mid-June to early September. Among them, 11 HREs occurred in late June to mid-August with distinct synoptic characteristics depending on the occurrence period. All HREs from 29 June to 27 July (P1) were triggered by extratropical cyclones, while those from 28 July to 15 August (P2) mainly occurred along the monsoon rainband. We argue that their transition is associated with atmospheric teleconnections. During P1, the western North Pacific subtropical high (WNPSH) anomalously extended westward, but its northward expansion was hindered by the meridional wave train from the suppressed convection over the South China Sea. This condition prevented a northward migration of the monsoon rainband but allowed more extratropical cyclones to pass over the Korean Peninsula, resulting in four HREs. During P2, the South China Sea convection was enhanced, and its circulation response prompted an abrupt northward expansion of the WNPSH with a large pressure gradient along its northern boundary. With intensified southwesterly moisture transport, a monsoon rainband was activated over the Korean Peninsula, producing six HREs. The opposite phases of the summer North Atlantic Oscillation, i.e., negative in P1 but positive in P2, further contributed to the anomalous monsoon circulation by modulating the midlatitude circulation response to the South China Sea convection. This study demonstrates that the nature of summertime HREs in East Asia can be strongly modulated by remote forcings.

Abstract

This paper documents time mean simulation characteristics from the ocean and sea ice components in a new coupled climate model developed at the NOAA Geophysical Fluid Dynamics Laboratory (GFDL). The GFDL Climate Model version 3 (CM3) is formulated with effectively the same ocean and sea ice components as the earlier CM2.1 yet with extensive developments made to the atmosphere and land model components. Both CM2.1 and CM3 show stable mean climate indices, such as large-scale circulation and sea surface temperatures (SSTs). There are notable improvements in the CM3 climate simulation relative to CM2.1, including a modified SST bias pattern and reduced biases in the Arctic sea ice cover. The authors anticipate SST differences between CM2.1 and CM3 in lower latitudes through analysis of the atmospheric fluxes at the ocean surface in corresponding Atmospheric Model Intercomparison Project (AMIP) simulations. In contrast, SST changes in the high latitudes are dominated by ocean and sea ice effects absent in AMIP simulations. The ocean interior simulation in CM3 is generally warmer than in CM2.1, which adversely impacts the interior biases.

Abstract

The authors present results for simulated climate and climate change from a newly developed high-resolution global climate model [Geophysical Fluid Dynamics Laboratory Climate Model version 2.5 (GFDL CM2.5)]. The GFDL CM2.5 has an atmospheric resolution of approximately 50 km in the horizontal, with 32 vertical levels. The horizontal resolution in the ocean ranges from 28 km in the tropics to 8 km at high latitudes, with 50 vertical levels. This resolution allows the explicit simulation of some mesoscale eddies in the ocean, particularly at lower latitudes.

Analyses are presented based on the output of a 280-yr control simulation; also presented are results based on a 140-yr simulation in which atmospheric CO₂ increases at 1% yr⁻¹ until doubling after 70 yr.

Results are compared to GFDL CM2.1, which has somewhat similar physics but a coarser resolution. The simulated climate in CM2.5 shows marked improvement over many regions, especially the tropics, including a reduction in the double ITCZ and an improved simulation of ENSO. Regional precipitation features are much improved. The Indian monsoon and Amazonian rainfall are also substantially more realistic in CM2.5.

The response of CM2.5 to a doubling of atmospheric CO₂ has many features in common with CM2.1, with some notable differences. For example, rainfall changes over the Mediterranean appear to be tightly linked to topography in CM2.5, in contrast to CM2.1 where the response is more spatially homogeneous. In addition, in CM2.5 the near-surface ocean warms substantially in the high latitudes of the Southern Ocean, in contrast to simulations using CM2.1.

Abstract

The Geophysical Fluid Dynamics Laboratory (GFDL) has developed a coupled general circulation model (CM3) for the atmosphere, oceans, land, and sea ice. The goal of CM3 is to address emerging issues in climate change, including aerosol–cloud interactions, chemistry–climate interactions, and coupling between the troposphere and stratosphere. The model is also designed to serve as the physical system component of earth system models and models for decadal prediction in the near-term future—for example, through improved simulations in tropical land precipitation relative to earlier-generation GFDL models. This paper describes the dynamical core, physical parameterizations, and basic simulation characteristics of the atmospheric component (AM3) of this model. Relative to GFDL AM2, AM3 includes new treatments of deep and shallow cumulus convection, cloud droplet activation by aerosols, subgrid variability of stratiform vertical velocities for droplet activation, and atmospheric chemistry driven by emissions with advective, convective, and turbulent transport. AM3 employs a cubed-sphere implementation of a finite-volume dynamical core and is coupled to LM3, a new land model with ecosystem dynamics and hydrology. Its horizontal resolution is approximately 200 km, and its vertical resolution ranges approximately from 70 m near the earth’s surface to 1 to 1.5 km near the tropopause and 3 to 4 km in much of the stratosphere. Most basic circulation features in AM3 are simulated as realistically, or more so, as in AM2. In particular, dry biases have been reduced over South America. In coupled mode, the simulation of Arctic sea ice concentration has improved. AM3 aerosol optical depths, scattering properties, and surface clear-sky downward shortwave radiation are more realistic than in AM2. The simulation of marine stratocumulus decks remains problematic, as in AM2. The most intense 0.2% of precipitation rates occur less frequently in AM3 than observed. The last two decades of the twentieth century warm in CM3 by 0.32°C relative to 1881–1920. The Climate Research Unit (CRU) and Goddard Institute for Space Studies analyses of observations show warming of 0.56° and 0.52°C, respectively, over this period. CM3 includes anthropogenic cooling by aerosol–cloud interactions, and its warming by the late twentieth century is somewhat less realistic than in CM2.1, which warmed 0.66°C but did not include aerosol–cloud interactions. The improved simulation of the direct aerosol effect (apparent in surface clear-sky downward radiation) in CM3 evidently acts in concert with its simulation of cloud–aerosol interactions to limit greenhouse gas warming.