Kyozo Ueyoshi

A time series of photosynthetically available radiation at the ocean surface from SeaWiFS and MODIS data

A global, 13-year record of photo-synthetically available radiation (PAR) at the ocean surface (9-km resolution) has been generated from SeaWiFS, MODIS-Aqua, and MODIS-Terra data. The PAR values are essentially obtained by subtracting from the solar irradiance at the top of the atmosphere (known) the solar energy reflected by the oceanatmosphere system (satellite-derived) and absorbed by the atmosphere (modeled). Observations by individual instruments, combinations of two instruments, and three instruments are considered in the calculations. Spatial and temporal biases between estimates from one, two, or three instruments are determined and corrected, resulting in a consistent time series for variability studies. Uncertainties are quantified on daily, weekly, and monthly time scales for the various instrument combinations from comparisons with in situ measurements. The correlative behavior of PAR, sea surface temperature, and chlorophyll concentration in the Equatorial Pacific is examined. PAR monitoring will continue with current and future satellite ocean-color sensors, in particular VIIRS, and the methodology will be extended to generating UV-A and UV-B irradiance.

Simulation and prediction of the Catalina Eddy

Abstract Observational studies generally suggest that the formation of the Catalina Eddy in the bight of southern California results from interaction between the synoptic-scale northerly flow and the topographic barrier along the southern California coast. In an attempt to better understand the eddy generation mechanisms, a high-resolution mesoscale model is initialized and forced on the lateral boundaries by NMCs large-scale objective analysis, and a detailed numerical study of the 26–30 June 1988 Catalina Eddy event is presented. The model results compare favorably with the observations and generally support the aforementioned mechanism of the eddy formation. It appears that a warm air mass over the bight resulting from adiabatic heating of low-level downslope flow deflected by the mountain barrier significantly helps create the alongshore and offshore pressure gradients favorable for the generation of a cyclonic vorticity. Although current operational forecast models are capable of often accurately pr...

Comparison of NMC's Global Pressure Analysis to NCDC's U.S. Observations

Abstract The National Meteorological Centers (NMCs) twice-daily, global 2.5° pressure analyses of temperature, relative humidity, and wind speed are compared, over the coterminous United States, to the National Climatic Data Centers twice-daily, upper-air rawinsonde observations and hourly, first-order, surface observations for the period 1 January 1988 through 31 December 1992. NMCs analyses have clearly improved during this time period. Still, there are some noticeable differences especially near the surface and at 1200 UTC. During the early morning there is a warm bias, relative humidity is too low, and the surface wind speed is too strong. Weaker systematic errors occur during the late afternoon: there is a cold bias, relative humidity is too high, and the surface wind speed is still too strong. Aloft, the bias is noticeably reduced except for the wind speed, which is somewhat too weak. The analysis wind speed also has too strong temporal variations near the surface and too weak temporal variations...

Net primary productivity estimates and environmental variables in the Arctic Ocean: An assessment of coupled physical-biogeochemical models

The relative skill of 21 regional and global biogeochemical models was assessed in terms of how well the models reproduced observed net primary productivity (NPP) and environmental variables such as nitrate concentration (NO3), mixed layer depth (MLD), euphotic layer depth (Zeu), and sea ice concentration, by comparing results against a newly updated, quality-controlled in situ NPP database for the Arctic Ocean (1959–2011). The models broadly captured the spatial features of integrated NPP (iNPP) on a pan-Arctic scale. Most models underestimated iNPP by varying degrees in spite of overestimating surface NO3, MLD, and Zeu throughout the regions. Among the models, iNPP exhibited little difference over sea ice condition (ice-free versus ice-influenced) and bottom depth (shelf versus deep ocean). The models performed relatively well for the most recent decade and toward the end of Arctic summer. In the Barents and Greenland Seas, regional model skill of surface NO3 was best associated with how well MLD was reproduced. Regionally, iNPP was relatively well simulated in the Beaufort Sea and the central Arctic Basin, where in situ NPP is low and nutrients are mostly depleted. Models performed less well at simulating iNPP in the Greenland and Chukchi Seas, despite the higher model skill in MLD and sea ice concentration, respectively. iNPP model skill was constrained by different factors in different Arctic Ocean regions. Our study suggests that better parameterization of biological and ecological microbial rates (phytoplankton growth and zooplankton grazing) are needed for improved Arctic Ocean biogeochemical modeling.

Influence of solar radiation absorbed by phytoplankton on the thermal structure and circulation of the tropical Atlantic Ocean

Numerical experiments conducted with an ocean general ocean circulation model reveal the potential influence of solar radiation absorbed by phytoplankton on the thermal structure and currents of the Tropical Atlantic Ocean. In the model, solar radiation penetration is parameterized explicitly as a function of chlorophyll-a concentration, the major variable affecting water turbidity in the open ocean. Two types of runs are performed, a clear water (control) run with a constant minimum chlorophyll-a concentration of 0.02 mgm-3, and a turbid water (chlorophyll) run with space- and time-varying chlorophyll-a concentration from satellite data. The difference between results from the two runs yields the biological effects. In the chlorophyll run, nutrients and biology production are implicitly taken into account, even though biogeochemical processes are not explicitly included, since phytoplankton distribution, prescribed from observations, is the result of those processes. Due to phytoplankton-radiation forcing, the surface temperature is higher by 1-2 K on average annually in the region of the North Equatorial current, the Northern part of the South Equatorial current, and the Caribbean system, and by 3-4 K in the region of the Guinea current. In this region, upwelling is reduced, and heat trapped in the surface layers by phytoplankton is not easily removed. The surface temperature is lower by 1 K in the Northern region of the Benguela current, due to increased upwelling. At depth, the equatorial Atlantic is generally cooler, as well as the eastern part of the tropical basin (excluding the region of the sub-tropical gyres). The North and South equatorial currents, as well as the Equatorial undercurrent, are enhanced by as much as 3-4 cms-1, and the circulation of the subtropical gyres is increased. Pole-ward heat transport is slightly reduced North of 35°N, suggesting that phytoplankton, by increasing the horizontal return flow in the subtropical region, may exert a cooling influence on higher latitude regions. The findings indicate that biology-induced buoyancy plays a significant role, in an indirect if not direct way, in the variability of the Tropical Atlantic Ocean, with consequences on atmospheric circulation and climate.

Chapter 11 Potential Feedback Mechanism Between Phytoplankton and Upper Ocean Circulation with Oceanic Radiative Transfer Processes Influenced by Phytoplankton – Numerical Ocean General Circulation Models and an Analytical Solution

Abstract Because of the diversity of the ecosystem in the earth, modeling of such an ecosystem cannot avoid arguing which ecosystem element should be included or excluded. We demonstrated that views of thermodynamics ensuring the flow of solar energy between nonliving things and living things in the oceanic ecosystem as an alternative approach in the modeling of the earth system with life. We showed that marine phytoplankton influence the global pattern of the sea surface temperature, seawater density, and associated flows by heat release to the upper ocean environment. The effect of heat release by phytoplankton on penetrative radiation not only influences directly the vertical structure of seawater density, but also dynamically interacts with surrounding ocean fluids in the equatorial Pacific. Numerical models experiments suggest an active role of phytoplankton in the equatorial ocean dynamics by modifying density and thus providing conditions favorable to phytoplankton growth, i.e., the potential positive feedback mechanism between the ecosystem and the ocean dynamics. A mechanistic model proposed here is simple enough to identify the cause-and-effect relationship of the phytoplanktons active role in the earth system.

Sensitivity of equatorial Pacific Ocean circulation to solar radiation absorbed by phytoplankton

Sensitivity experiments conducted with the MIT ocean general circulation model reveal the potential influence of solar radiation absorbed by phytoplankton on the thermal structure and currents of the equatorial Pacific Ocean. In the model, vertical attenuation of solar radiation is parameterized as a function of chlorophyll pigment concentration, the major variable affecting turbidity in the euphotic zone. To isolate turbidity effects, the model is run from 1948 to 2001 with either a constant minimum pigment concentration of 0.02 mgm^-3 during the entire period or spatially and temporally varying pigment concentration from the Sea-viewing Wide Field-of-view Sensor during 1997-2001. The two model runs are compared for 2001, a relatively normal year following the strong 1997-1998 El Nino and subsequent La Nina. Due to phytoplankton-radiation forcing, equatorial sea surface temperature is decreased by 0.3K on average annually between 100W and 160W, but the negative temperature change is more pronounced in sub-surface layers, reaching -1.5K at 110W. In that region, heat trapping by phytoplankton causes the mixed layer to shallow and isotherms to shoal toward the equator, generating geostrophic currents that enhance the south equatorial current. These surface currents diverge north and south of the equator as they progress westward, creating equatorial divergence, convergence at the level of the equatorial undercurrent, and upwelling, explaining the change in thermal structure. The equatorial undercurrent is strengthened by as much as 4 cms-1 at its core. The findings support previous results obtained with the MHI Ocean isoPYCnal general circulation model and pigment concentration from the Coastal Zone Color Scanner. They indicate that biology-induced buoyancy my play a significant role in the equatorial Pacific Ocean circulation and suggest the existence of a biophysical feedback mechanism that contributes to maintaining the cold tongue in the eastern equatorial Pacific Ocean, with implications for inter-annual variability associated with El Nino.