Yoko Tsushima

Bio: Yoko Tsushima is an academic researcher from University of Tokyo. The author has contributed to research in topics: Radiative transfer & Climate model. The author has an hindex of 4, co-authored 7 publications receiving 394 citations.

Modeling of the radiative process in an atmospheric general circulation model

Abstract: A new radiation scheme has been developed for dynamic general-circulation modeling An automatic determination of k-distribution parameters and a treatment of solar–terrestrial radiation interacting with gaseous and particulate matter are incorporated into the scheme by a technique that combines discrete ordinate and matrix operator methods An accelerated scheme for cloud overlap is developed and tested The resultant accuracy of the scheme is ±05 K/day to a 70-km height in clear sky better than that of the line-by-line calculation method

Radiative forcing by contrails

Abstract: . A parametric study of the instantaneous radiative impact of contrails is presented using three different radiative transfer models for a series of model atmospheres and cloud parameters. Contrails are treated as geometrically and optically thin plane parallel homogeneous cirrus layers in a static atmosphere. The ice water content is varied as a function of ambient temperature. The model atmospheres include tropical, mid-latitude, and subarctic summer and winter atmospheres. Optically thin contrails cause a positive net forcing at top of the atmosphere. At the surface the radiative forcing is negative during daytime. The forcing increases with the optical depth and the amount of contrail cover. At the top of the atmosphere, a mean contrail cover of 0.1% with average optical depth of 0.2 to 0.5 causes about 0.01 to 0.03 Wm-2 daily mean instantaneous radiative forcing. Contrails cool the surface during the day and heat the surface during the night, and hence reduce the daily temperature amplitude. The net effect depends strongly on the daily variation of contrail cloud cover. The indirect radiative forcing due to particle changes in natural cirrus clouds may be of the same magnitude as the direct one due to additional cover. Key words. Atmospheric composition and structure (aerosols and particles) · Meteorology and atmospheric dynamics (climatology · radiative processes)

Comparison of equilibrium and transient responses to CO2 increase in eight state-of-the-art climate models

Abstract: We compared the climate response of doubled CO 2 equilibrium experiments (2 × CO 2 ) by atmosphere–slab ocean coupled general circulation models (ASGCMs) and that of 1% per year CO 2 increase experiments (1%CO 2 by atmosphere–ocean coupled general circulation models (AOGCMs) using eight state-of-the-art climate models. Climate feedback processes in 2 × CO 2 are different from those in 1%CO 2 , and the equilibrium climate sensitivity (T 2× ) in 2 × CO 2 is different from the effective climate sensitivity (T 2×,eff ) in 1%CO 2 . The difference between T 2× and T 2×,eff is from −1.3 to 1.6 K, a large part of which can be explained by the difference in the ice-albedo and cloud feedback. The largest contribution is cloud SW feedback, and the difference in cloud SW feedback for 2 × CO 2 and 1%CO 2 could be determined by the distribution of the SAT anomaly which causes differences in the atmospheric thermal structure. An important factor which determines the difference in ice-albedo feedback is the initial sea ice distribution at the Southern Ocean, which is generally overestimated in 2 × CO 2 as compared to 1%CO 2 and observation. Through the comparison of climate feedback processes in 2 ×CO 2 and 1%CO 2 , the possible behaviour of the time evolution of T 2×,eff is discussed.

Time evolutions of various radiative forcings for the past 150 years estimated by a general circulation model

Abstract: [1] Time series of the instantaneous radiative forcings for main anthropogenic and natural forcing agents from the year 1850 to 2000 are evaluated at the Earth's surface as well as at the tropopause with an atmospheric general circulation model. This evaluation corresponds to a simulation of 20th century climate with a synthetic coupled atmosphere-ocean general circulation model. The evaluation indicates that the positive radiative forcing at the tropopause rapidly increases from 1910 to 1950 and after 1970 principally due to long-lived greenhouse gases, while the negative radiative forcing at the surface sharply increases between 1955 and 1965 mainly due to the aerosol direct and indirect effects. This study suggests that a simultaneous analysis of changing rates of the radiative forcing both at the tropopause and surface can explain tendencies of changes in the surface air temperature.

Comparison of equilibrium and transient responses to CO2 increase in eight state-of-the-art climate models

Abstract: We compared the climate response of doubled CO 2 equilibrium experiments (2 x CO 2 ) by atmosphere-slab ocean coupled general circulation models (ASGCMs) and that of 1% per year CO 2 increase experiments (1%CO 2 by atmosphere-ocean coupled general circulation models (AOGCMs) using eight state-of-the-art climate models. Climate feedback processes in 2 x CO 2 are different from those in 1 %CO 2 , and the equilibrium climate sensitivity (T 2x ) in 2 x CO 2 is different from the effective climate sensitivity (T 2x.cff ) in 1%CO 2 . The difference between T 2x and T 2x.cff is from - 1.3 to 1.6 K, a large part of which can be explained by the difference in the ice-albedo and cloud feedback. The largest contribution is cloud SW feedback, and the difference in cloud SW feedback for 2 x CO 2 and 1%CO 2 could be determined by the distribution of the SAT anomaly which causes differences in the atmospheric thermal structure. An important factor which determines the difference in ice-albedo feedback is the initial sea ice distribution at the Southern Ocean, which is generally overestimated in 2 x CO 2 as compared to 1%CO 2 and observation. Through the comparison of climate feedback processes in 2 x CO 2 and 1%CO 2 , the possible behaviour of the time evolution of T 2x.cff is discussed.

Estimates of the direct and indirect radiative forcing due to tropospheric aerosols: A review

Abstract: This paper reviews the many developments in estimates of the direct and indirect global annual mean radiative forcing due to present-day concentra- tions of anthropogenic tropospheric aerosols since Inter- governmental Panel on Climate Change (1996). The range of estimates of the global mean direct radiative forcing due to six distinct aerosol types is presented. Addition- ally, the indirect effect is split into two components corresponding to the radiative forcing due to modifica- tion of the radiative properties of clouds (cloud albedo effect) and the effects of anthropogenic aerosols upon the lifetime of clouds (cloud lifetime effect). The radia- tive forcing for anthropogenic sulphate aerosol ranges from 20.26 to 20.82 W m 22 . For fossil fuel black carbon the radiative forcing ranges from 10.16 W m 22 for an external mixture to 10.42 W m 22 for where the black carbon is modeled as internally mixed with sulphate aerosol. For fossil fuel organic carbon the two estimates of the likely weakest limit of the direct radiative forcing are 20.02 and 20.04 W m 22 . For biomass-burning sources of black carbon and organic carbon the com-

Radiative forcing of climate change

Abstract: Our current understanding of mechanisms that are, or may be, acting to cause climate change over the past century is briefly reviewed, with an emphasis on those due to human activity. The paper discusses the general level of confidence in these estimates and areas of remaining uncertainty. The effects of increases in the so-called well-mixed greenhouse gases, and in particular carbon dioxide, appear to be the dominant mechanism. However, there are considerable uncertainties in our estimates of many other forcing mechanisms; those associated with the so-called indirect aerosol forcing (whereby changes in aerosols can impact on cloud properties) may be the most serious, as its climatic effect may be of a similar size as, but opposite sign to, that due to carbon dioxide. The possible role of volcanic eruptions as a natural climate change mechanism is also highlighted.

Emulating coupled atmosphere-ocean and carbon cycle models with a simpler model, MAGICC6 - Part 1: Model description and calibration

Abstract: Current scientific knowledge on the future response of the climate system to human-induced perturbations is comprehensively captured by various model intercomparison efforts In the preparation of the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC), intercomparisons were organized for atmosphere-ocean general circulation models (AOGCMs) and carbon cycle models, named "CMIP3" and "C 4 MIP", respectively Despite their tremendous value for the scientific community and policy makers alike, there are some difficulties in interpreting the results For example, radiative forcings were not standardized across the various AOGCM integrations and carbon cycle runs, and, in some models, key forcings were omitted Furthermore, the AOGCM analysis of plausible emissions pathways was restricted to only three SRES scenarios This study attempts to address these issues We present an updated version of MAGICC, the simple carbon cycle-climate model used in past IPCC Assessment Reports with enhanced representation of time-varying climate sensitivities, carbon cycle feedbacks, aerosol forcings and ocean heat uptake characteristics This new version, MAGICC6, is successfully calibrated against the higher complexity AOGCMs and carbon cycle models Parameterizations of MAGICC6 are provided The mean of the emulations presented here using MAGICC6 deviates from the mean AOGCM responses by only 22% on average for the SRES scenarios This enhanced emulation skill in comparison to previous calibrations is primarily due to: making a "like-with-like comparison" using AOGCM-specific subsets of forcings; employing a new calibration procedure; as well as the fact that the updated simple climate model can now successfully emulate some of the climate-state dependent effective climate sensitivities of AOGCMs The diagnosed effective climate sensitivity at the time of CO 2 doubling for the AOGCMs is on average 288 °C, about 033 °C cooler than the mean of the reported slab ocean climate sensitivities In the companion paper (Part 2) of this study, we examine the combined climate system and carbon cycle emulations for the complete range of IPCC SRES emissions scenarios and the new RCP pathways