Abstract. Wind work at the air-sea interface is the transfer of kinetic energy between the ocean and the atmosphere and, as such, is an important part of the atmosphere-ocean coupled system. Since wind work involves winds and ocean currents that span a broad range of spatial and temporal scales, a comprehensive study would require access to observations of a wide range of space and time scales. In the absence of appropriate global observations, our study makes use of a new, global, coupled ocean-atmosphere simulation with horizontal grid spacing of 2–5 km for the ocean and 7 km for the atmosphere. Here we develop a methodology, both in physical and spectral space, to diagnose different components of wind work in terms of forcing distinct classes of oceanic motions, including mean currents, time-dependent large-scale currents and mesoscale eddies, and internal gravity waves such as near-inertial waves. The total simulated wind work has a magnitude of 5.21 TW, a value much larger than reported by previous modeling studies. The total wind work is first decomposed into time-mean and time-dependent components, with the former accounting for 2.23 TW (43 %) and the latter 2.98 TW (57 %). The time-dependent wind work is then decomposed into two components, a high-frequency component that forces internal gravity waves and a low-frequency component that forces mesoscale eddies and large-scale currents. The high-frequency component is positive at scales between 10 km and 1000 km and represents 75 % of the total time-dependent component. The low-frequency component is found to be positive for spatial scales larger than 275 km and ten times larger than the negative part associated with smaller spatial scales. The negative wind work acts as a surface drag that slows down surface currents and damps mesoscale eddies whereas the positive low-frequency part accelerates large-scale currents. The complex and consequential interplay of surface winds and currents in the numerical simulation motivates the need for a winds-and-currents satellite mission to directly observe these wind work components.
The planetary boundary layer (PBL) is central to the exchange of heat and moisture between the Earth’s surface and the atmosphere, to the turbulent transport of aerosol and chemical pollutants affecting air quality, and to near- and long-term climate prediction. Consequently, the PBL has become a major focus of atmospheric and climate science, particularly after its designation as a ’targeted observable’ by the 2018 National Academy of Science, Engineering and Medicine Earth Science Decadal Survey. Information about the height of the PBL that is global in scope allows for wide geographical analysis of connections to seasonality, to latitude, proximity to oceans and synoptic variability. Information about the PBL height at hourly resolution allows for the analysis of diurnal cycles and PBL height growth rates, both of which are critical to the study of near-surface transport processes. This manuscript describes the release of a new global data set of PBL height estimates retrieved from radar wind profilers (RWPs), called GRWP-PBLH: Global RadarWind Profiler Planetary Boundary Layer Height. Hourly PBL height estimates are retrieved using an existing algorithm applied to archived signal to noise ratio data from a series of networks located around the globe, specifically in Australia, Europe and Japan. Information about the source data, details of data processing and production of PBL height estimates are discussed here along with a description of supplementary data and the available software. The GRWP-PBLH data set is now accessible to the community for ongoing and future research.
To predict the future climate on multiyear timescales, it is crucial to understand how the changing external radiative forcing (CO2 and Ozone) drives the climate and impacts the skill of intra-seasonal to multiyear climate prediction. In this study, we use a 1-degree configuration of the GEOS-MITgcm coupled general circulation model to understand the response to different levels of observed external forcing from past decades. We ran `perpetual' experiments for 1992, 2000, and 2020, each with their respective year’s external forcing. Results of the perpetual simulations showed that the Northern Hemisphere polar stratospheric temperature increases from 1992 to 2000, whereas it decreases from 2000 to 2020. We further conducted a 10-member ensemble of transient climate simulations for the 1992--2020 period with observed external forcing and found a similar positive temperature trend from 1992 to 2000 and a negative trend from 2000 to 2020. This is in contrast to the general expectation that the stratosphere cools as CO2 increases. A similar opposing pattern of temperature trends exists in reanalyses and CMIP6 historical simulations with a well-resolved stratosphere. Analysis of the results showed that the external forcing change during the years 1992-2000 increases the tropical diabatic heating, and intensifies the wave activity related meridional heat transport to the Northern Hemisphere mid to high-latitudes, which, in turn, increases the polar stratospheric temperature. In contrast, during the 2000-2020 period the meridional heat transport decreases, contributing to a decrease in the polar stratospheric temperature. The long-wave radiation change in these periods responds to the changing temperature and so doesn't play a significant role in driving them.
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