An intercomparison between the GSWM, UARS, and ground based radar observations: a case-study in January 1993

The Global-Scale Wave Model (GSWM) is a steady-state two-dimensional linearized model capable of simulating the solar tides and planetary waves. In an effort to understand the capabilities and limitations of the GSWM throughout the upper mesosphere and thermosphere a comparative analysis with observational data is presented. A majority of the observational data used in this study was collected during the World Day campaign which ran from 20 January to 30 January 1993. During this campaign data from 18 ground-based observational sites across the globe and two instruments located on the UARS spacecraft were analyzed. Comparisons of these data with the simulations from the GSWM indicate that the GSWM results are in reasonable agreement with the observations. However, there are a number of cases where the agreement is not particularly good. One such instance is for the semidiurnal tide in the northern hemisphere, where the GSWM estimates may exceed observations by 50%. Through a number of numerical simulations, it appears that this discrepancy may be due to the eddy diffusivity profiles used by the GSWM. Other differences relating to the diurnal tide and the quasi-two-day wave are presented and discussed. Additionally, a discussion on the biases and aliasing difficulties which may arise in the observational data is alos presented.     

Diurnal variations of the planetary boundary layer observed with anL-band clear-air doppler radar

Based on continuous observations of the planetary boundary layer (PBL) with anL-band (1357.5 MHz) boundary-layer radar (BLR) at a hilly location in Japan, we have discovered that on clear days, a thin enhanced echo layer corresponding to the top of the PBL (or mixed layer) appeared at about 500 m height in the morning and ascended to about 1500 m in the afternoon. Strong upward velocities were observed below the echo layer (or inside the PBL), reaching 1500 m in the afternoon.     

Laboratory Study of O(1S) Formation Process in the Photolysis of O3 and its Atmospheric Implications

A high-sensitive technique to detect O(¹S) atoms using vacuum ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy has been applied to study the O(¹S) production process from the UV photodissociation of O₃, N₂O, and H₂O₂. The quantum yields for O(¹S) formation from O₃ photolysis at 215 and 220 nm are determined to be (1.4 ± 0.4) × 10⁻⁴ and (5 ± 3) × 10⁻⁵, respectively. Based on thermochemical considerations, the O(¹S) formation from O₃ photolysis at 215 and 220 nm is attributed to a spin-forbidden process of O(¹S)+O₂(X³Σ_g ⁻). Analysis of the Doppler profile of O(¹S) produced from O₃ photolysis at 193 nm also indicates that the O(¹S) atoms are produced from the spin-forbidden process. In the photolysis of N₂O and H₂O₂ at 193 nm, no discernible signal of O(¹S) atoms has been detected. The upper limit values of the quantum yields for O(¹S) production from N₂O and H₂O₂ photolysis at 193 nm are estimated to be 8 × 10⁻⁵ and 3 × 10⁻⁵, respectively. Using the experimental results, the impact of the O(¹S) formation from O₃ photolysis on the atmospheric OH radical formation through the reaction of O(¹S)+H₂O has been estimated. The calculated results show that the contribution of the O(¹S)+H₂O reaction to the OH production rate is ∼2% of that of the O(¹D)+H₂O reaction at 30 km altitude in mid-latitude. Implications of the present laboratory experimental results for the terrestrial airglow of O(¹S) at 557.7 nm have also been discussed.     

Impacts of the South China Sea Throughflow on seasonal and interannual variations of the Indonesian Throughflow

Impacts of the South China Sea Throughflow (SCST) on seasonal and interannual variations of the Indonesian Throughflow are studied by comparing outputs from ocean general circulation model (OGCM) experiments with and without the SCST. The observed subsurface maximum in the southward flow through the Makassar Strait is simulated only when the SCST, which is driven by the large-scale wind, is allowed in the model. The mean volume and heat transport by the Makassar Strait Throughflow are reduced by 1.7 Sv and 0.19 PW, respectively, by the existence of the SCST in the model. The difference is particularly remarkable during boreal winter when the SCST reaches its seasonal maximum. Furthermore, the SCST is strengthened during El Niño, leading to the weakening in the southward volume and heat transport through the Makassar Strait by 0.37 Sv and 0.05 PW, respectively. These findings from the OGCM experiments suggest that the SCST may play an important role in climate variability of the Indo-Pacific Ocean.     

Respective influences of IOD and ENSO on the Tibetan snow cover in early winter

Using reanalysis data and snow cover data derived from satellite observations, respective influences of Indian Ocean Dipole (IOD) and El Niño/Southern Oscillation (ENSO) on the Tibetan snow cover in early winter are investigated. It is found that the snow cover shows a significant positive partial correlation with IOD. In the pure positive IOD years with no co-occurrences of El Niño, negative geopotential height anomalies north of India are associated with warm and humid southwesterlies to enter the plateau from the Bay of Bengal after rounding cyclonically and supply more moisture. This leads to more precipitation, more snow cover, and resultant lower surface temperature over the plateau. These negative geopotential height anomalies north of India are related to the equivalent barotropic stationary Rossby waves in the South Asian wave guide. The waves can be generated by the IOD-related convection anomalies over the western/central Indian Ocean. In contrast, in the pure El Niño years with no co-occurrences of the positive IOD, the anomalies of moisture supply and surface temperature over the plateau are insignificant, suggesting negligible influences of ENSO on the early winter Tibetan snow cover. Further analyses show that ENSO is irrelevant to the spring/early summer Tibetan snow cover either, whereas the IOD-induced snow cover anomalies can persist long from the early winter to the subsequent early summer.     

Transient wave activity and its fluxes in the North Atlantic Ocean simulated by a global eddy-resolving model

Eight-year daily mean output of a quasi-global eddy-resolving model is examined with a focus on the large-scale dynamical characteristics of the North Atlantic Ocean in a framework of potential vorticity (PV) and its derivatives. The model has reproduced some of the observed features of the mean potential vorticity field well. The three-dimensional structure of the mean potential vorticity supports baroclinic instability in most of the basin. Eddies are found to play important roles in the formation and maintenance of the mean potential vorticity fields. The contribution of relative vorticity to the mean potential vorticity field is found to be negligible for the most part. However, relative vorticity contribution to the source/sink of potential vorticity and eddy potential enstrophy is not negligible. We also find that eddies are not necessarily diffusive even on a basin-scale.     

A low-carbon society: global visions,pathways, and challenges

The feasibility of two low-carbon society (LCS) scenarios, one with and one without nuclear power and carbon capture and storage (CCS), is evaluated using the AIM/Enduse[Global] model. Both scenarios suggest that achieving a 50% emissions reduction target (relative to 1990 levels) by 2050 is technically feasible if locally suited technologies are introduced and the relevant policies, including necessary financial transfers, are appropriately implemented. In the scenario that includes nuclear and CCS options, it will be vital to consider the risks and acceptance of these technologies. In the scenario without these technologies, the challenge will be how to reduce energy service demand. In both scenarios, the estimated investment costs will be higher in non-Annex I countries than in Annex I countries. Finally, the enhancement of capacity building to support the deployment of locally suited technologies will be central to achieving an LCS.

Policy relevance

Policies to reduce GHG emissions up to 2050 are critical if the long-term target of stabilizing the climate is to be achieved. From a policy perspective, the cost and social acceptability of the policy used to reduce emissions are two of the key factors in determining the optimal pathways to achieve this. However, the nuclear accident at Fukushima highlighted the risk of depending on large-scale technologies for the provision of energy and has led to a backlash against the use of nuclear technology. It is found that if nuclear and CCS are used it will be technically feasible to halve GHG emissions by 2050, although very costly. However, although the cost of halving emissions will be about the same if neither nuclear nor CCS is used, a 50% reduction in emissions reduction will not be achievable unless the demand for energy service is substantially reduced.     

How is the Indian Ocean Subtropical Dipole excited?

Based on experiments using a coupled general circulation model which resolves tropical ocean–atmosphere coupled phenomena such as El Niño/Southern Oscillation (ENSO) and the Indian Ocean Dipole, forcing mechanisms of the Indian Ocean subtropical dipole (IOSD) are investigated. In the control experiment, as in the observation, several types of the IOSD are generated by the variations in the Mascarene High during austral summer and characterized by a dipole pattern of sea surface temperature (SST) anomalies in the northeastern and southwestern parts of the southern Indian Ocean. In another experiment, where the SST outside the southern Indian Ocean is nudged toward the monthly climatology of the simulated SST, one type of the IOSD occurs, but it is less frequent and associated with the zonal wavenumber four pattern of equivalently barotropic geopotential height anomalies in high latitudes, suggesting an interesting link with the Antarctic Circumpolar Wave. This indicates that, even without the atmospheric teleconnection from tropical coupled climate modes, the IOSD may develop in association with the atmospheric variability in high latitudes of the Southern Hemisphere. In the other experiment, where only the southern Indian Ocean and the tropical Pacific are freely interactive with the atmosphere, two types of both positive and negative IOSD occur. Since the occurrence frequency of the IOSD significantly increases as compared to the second experiment, this result confirms that the atmospheric teleconnection from ocean-atmosphere coupled modes in the tropical Pacific such as ENSO may also induce the variations in the Mascarene High that generate the IOSD. The present research, even within the realm of model studies, shows clearly that the predictability of the IOSD in mid-latitudes is related to both low and high-latitudes climate variations.