We present a new three-dimensional chemistry-climate model (CCM) called the “Meteorological Research Institute (MRI) Chemistry-Climate Model, version 2” (MRI-CCM2). The model treats chemical and physical processes interactively from the surface to the stratosphere to simulate the global distribution and evolution of ozone and other trace gases with a framework similar to that of version 1 (MRI-CCM1), which was a stratospheric model. We have added detailed tropospheric chemistry to Version 1 in order to seamlessly treat ozone chemistry in both the troposphere and stratosphere. The chemistry module of Version 2 includes 90 chemical species with 172 gas-phase reactions, 59 photolysis reactions and 16 heterogeneous reactions; includes improved grid-scale transport with a semi-Lagrangian scheme, sub grid-scale convective transportand turbulent diffusion, dry and wet deposition, and emissions of trace gases from various sources. We conducted a free run and an assimilated run towards observed atmospheric fields over 11 years, to reproduce the 1990s distribution of chemical constituents. The simulated seasonal cycle and geographical distribution of ozone below the middle troposphere are generally in good agreement with ozonesonde observations, although ozone was underestimated in the lower troposphere in the south polar region, and extratropical ozone was overestimated in the upper troposphere and lower stratosphere. Version 2 also reproduces realistic characteristics for other species such as carbon monoxide (CO), nitric oxide (NO), and the hydroxyl radical (OH): The model reproduces the observed seasonal cycle of CO well, although it overestimates CO by about 15 ppbv in the southern high latitudes; the vertical profiles of NO captures the observed features; and finally, distribution of the OH radical is similar to that simulated by other recent CCMs.
The recent uptake of anthropogenic carbon by the ocean brings about changes in the surface-ocean carbon cycle that could result in ocean acidification with subsequent serious effects on marine ecosystems. We evaluated the trend of ocean acidification in the surface layer of extensive regions of the subtropical North Pacific using synthesized data for partial pressure of CO2 for the past 40 years because no precise pH data were available. The results show significant trends of acidification (a pH decrease of 0.01 to 0.02 per decade) over the subtropical North Pacific. The rate of pH decrease, after excluding the contribution from changes in sea surface temperature, was highest in the eastern subtropical region. In this region in particular, the intrusion of subarctic waters with high concentrations of dissolved inorganic carbon could have contributed to the relatively high rate of acidification. Comparisons of the estimated rate of pH decrease for the past 26 years with those for the decade following 1969 and for 50 years into the future suggest an acceleration of acidification in recent years, as well as in the future, depending on the scenario of future anthropogenic CO2 emission.
Recent infrared sounders such as the Atmospheric Infrared Sounder and the Infrared Atmospheric Sounding Interferometer (IASI) have thousands of channels. Since the channels have fewer degrees of freedom than the number of channels, the channels are not independent, and thus correlations are expected among them. On examination of the transmittances of IASI channels, we found that many combinations of channels have high statistical correlations. Furthermore, the transmittances of 387 of the 616 IASI channels are statistically predictable from only 41 channels. An empirical estimation of transmittances by using a fast radiative transfer model greatly improved the computational efficiency of an atmospheric sounder.
We evaluated a new quick response dissolved oxygen (DO) sensor “RINKO”, currently under development by JFE Advantech Co., Ltd., to determine its in situ response and applicability to hydrographic and hydrochemical observations in the western North Pacific and in the Sea of Japan. The response time of the RINKO sensor to ambient DO changes was demonstrated at about 1 s in these in situ experiments. RINKO data were calibrated to temperature, pressure, and bottle sample DO data obtained by conventional Winkler method, yielding a precision of < ± 1 μmol kg-1, except in the upper layers of the ocean where vertical DO variations are large. Although the sensor was subject to instrumental drift during the period of a cruise (equivalent to < 6 μmol kg-1 DO) and to pressure hysteresis between downcasts and upcasts (< 4 μmol kg-1 DO), the RINKO sensor is capable of observing continuous vertical DO profiles with a precision that is sufficient for most practical purposes. The RINKO sensor will contribute to an improved understanding of DO variability, providing an expanded DO database with enhanced spatial and temporal resolution.