Atsumu Ohmura

Baseline Surface Radiation Network (BSRN/WCRP) : New precision radiometry for Climate Research

To support climate research, the World Climate Research Programme (WCRP) initiated a new radiometric network, the Baseline Surface Radiation Network (BSRN). The network aims at providing validation material for satellite radiometry and climate models. It further aims at detecting long-term variations in irradiances at the earth’s surface, which are believed to play an important role in climate change. The network and its instrumentation are designed 1) to cover major climate zones, 2) to provide the accuracy required to meet the objectives, and 3) to ensure homogenized standards for a long period in the future. The limits of the accuracy are defined to reach these goals. The suitable instruments and instrumentations have been determined and the methods for observations and data management have been agreed on at all stations. Measurements of irradiances are at 1 Hz, and the 1-min statistics (mean, standard deviation, and extreme values) with quality flags are stored at a centralized data archive at the WCRP’s World Radiation Monitoring Center (WRMC) in Zurich, Switzerland. The data are quality controlled both at stations and at the WRMC. The original 1-min irradiance statistics will be stored at the WRMC for 10 years, while hourly mean values will be transferred to the World Radiation Data Center in St. Petersburg, Russia. The BSRN, consisting of 15 stations, covers the earth’s surface from 80°N to 90°S, and will soon be joined by seven more stations. The data are available to scientific communities in various ways depending on the communication environment of the users. The present article discusses the scientific base, organizational and technical aspects of the network, and data retrieval methods; shows various application possibilities; and presents the future tasks to be accomplished.

Mass balance of glaciers and ice caps: Consensus estimates for 1961–2004

[1] Working with comprehensive collections of directly-measured data on the annual mass balance of glaciers other than the two ice sheets, we combine independent analyses to show that there is broad agreement on the evolution of global mass balance since 1960. Mass balance was slightly below zero around 1970 and has been growing more negative since then. Excluding peripheral ice bodies in Greenland and Antarctica, global average specific balance for 1961-1990 was -219 ± 112 kg m -2 a -1 , representing 0.33±0.17 mm SLE (sea-level equivalent) a -1 . For 2001-2004, the figures are -510 ± 101 kg m -2 a -1 and 0.77±0.15 mm SLE a -1 . Including the smaller Greenland and Antarctic glaciers, global total balance becomes 0.38 ± 0.19 mm SLE a -1 for 1961-1990 and 0.98 ± 0.19 mm SLE a -1 for 2001-2004. For 1991-2004 the glacier contribution, 0.77 ± 0.26 mm SLE a -1 , is 20-30% of a recent estimate of 3.2 ± 0.4 mm a -1 of total sea-level rise for 1993-2005. While our error estimates are not rigorous, we believe them to be liberal as far as they go, but we also discuss several unquantified biases of which any may prove to be significant.

Means and Trends of Shortwave Irradiance at the Surface Estimated from Global Energy Balance Archive Data

Abstract Means and trends of shortwave irradiance at the earth’s surface are calculated from pyranometer measurements stored in the Global Energy Balance Archive (GEBA) database. The GEBA database contains the most comprehensive set of shortwave irradiance monthly means. The relative random error of measurement is approximately 5% of a monthly mean in general and approximately 2% of a yearly mean. The shortwave irradiance yearly means are analyzed in a 2.5° × 2.5° grid. In average example grid cells in Europe (no large altitude differences, no coasts), the difference of shortwave irradiance yearly means measured at different stations (station effect) is less than 5% of the cell mean, and the interannual variability is approximately 4% of the cell mean. On most continents, shortwave irradiance decreases significantly in large regions, and significant positive trends are observed only in four small regions.

Validation of General Circulation Model Radiative Fluxes Using Surface Observations

Abstract The surface radiative fluxes of the ECHAM3 General Circulation Model (GCM) with T2 1, T42, and T 106 resolutions have been validated using observations from the Global Energy Balance Archive (GEBA, World Climate Program-Water Project A7). GEBA contains the most comprehensive dataset now available for worldwide instrumentally measured surface energy fluxes. The GCM incoming shortwave radiation at the surface has been compared with more than 700 long-term monitoring stations. The ECHAM3 models show a clear tendency to overestimate the global annual-mean incoming shortwave radiation at the surface due to an underestimation of atmospheric absorption. The model-calculated global-mean surface shortwave absorption around 165 W m−2 is estimated to be too high by 10–15 W m−2. A similar or higher overestimate is present in several other CYCMS. Deficiencies in the clear-sky absorption of the ECHAM3 radiation scheme are proposed as a contributor to the flux discrepancies. A stand-alone validation of the radi...

Data Quality Assessment and the Long-Term Trend of Ground Solar Radiation in China

Abstract Solar radiation is one of the most important factors affecting climate and the environment. Routine measurements of irradiance are valuable for climate change research because of long time series and areal coverage. In this study, a set of quality assessment (QA) algorithms is used to test the quality of daily solar global, direct, and diffuse radiation measurements taken at 122 observatories in China during 1957–2000. The QA algorithms include a physical threshold test (QA1), a global radiation sunshine duration test (QA2), and a standard deviation test applied to time series of annually averaged solar global radiation (QA3). The results show that the percentages of global, direct, and diffuse solar radiation data that fail to pass QA1 are 3.07%, 0.01%, and 2.52%, respectively; the percentages of global solar radiation data that fail to pass the QA2 and QA3 are 0.77% and 0.49%, respectively. The method implemented by the Global Energy Balance Archive is also applied to check the data quality of ...

A Possible Change in Mass Balance of Greenland and Antarctic Ice Sheets in the Coming Century

Abstract A high-resolution GCM is found to simulate precipitation and surface energy balance of high latitudes with high accuracy. This opens new possibilities to investigate the future mass balance of polar glaciers and its effect on sea level. The surface mass balance of the Greenland and the Antarctic ice sheets is simulated using the ECHAM3 GCM with TI06 horizontal resolution. With this model, two 5-year integrations for the present and doubled carbon dioxide conditions based on the boundary conditions provided by the ECHAM1/T21 transient experiment have been conducted. A comparison of the two experiments over Greenland and Antarctica shows to what extent the effect of climate change on the mass balance on the two largest glaciers of the world can differ. On Greenland one sees a slight decrease in accumulation and a substantial increase in melt, while on Antarctica a large increase in accumulation without melt is projected. Translating the mass balances into terms of sea-level equivalent. the Greenlan...

Evaluation of Downward Longwave Radiation in General Circulation Models

Abstract The longwave radiation emitted by the atmosphere toward the surface [downward longwave radiation (DLR)] is a crucial factor in the exchange of energy between the earth surface and the atmosphere and in the context of radiation-induced climate change. Accurate modeling of this quantity is therefore a fundamental prerequisite for a reliable simulation and projection of the surface climate in coupled general circulation models (GCM). DLR climatologies calculated in a number of GCMs and in a model in assimilation mode (reanalysis) are analyzed using newly available data from 45 worldwide distributed observation sites of the Global Energy Balance Archive (GEBA) and the Baseline Surface Radiation Network (BSRN). It is shown that substantial biases are present in the GCM-calculated DLR climatologies, with the GCMs typically underestimating the DLR (estimated here to be approximately 344 W m−2 globally). The biases are, however, not geographically homogeneous, but depend systematically on the prevailing ...

GCM-Simulated Surface Energy Fluxes in Climate Change Experiments

The changes in the surface energy fluxes calculated with a general circulation model under increased levels of carbon dioxide concentration are analyzed and related to the simulation of these fluxes under present-day conditions. It is shown that the errors in the simulated fluxes under present climate are often of similar or larger magnitude than the simulated changes of these quantities. A similar relationship may be found in climate change experiments of many GCMs. Although this does not imply that the projected changes of the fluxes are wrong, more accurate absolute values would improve confidence in GCM-simulated climate change scenarios. The global mean increase in the downward component of the longwave radiation, which is the direct greenhouse forcing at the surface, is on the order of 10 W m22 at the time of doubled carbon dioxide in a transient coupled atmosphere‐ocean scenario experiment. This is an amount similar to the underestimation of this quantity in the present-day simulations compared to surface observations. Thus, it is only with doubled carbon dioxide concentration that the simulated greenhouse forcing at the surface reaches the values observed at present. The simulated shortwave radiation budget at the surface is less affected by the increased levels of carbon dioxide than the longwave budget on the global scale. Regionally and seasonally, the changes in the incoming shortwave radiation at the surface can exceed 20 W m22, mainly due to changes in cloud amounts. The projected changes, however, are generally of smaller magnitude than the systematic errors in the control run at the majority of 720 observation sites. The positive feedback between excessive radiation and surface processes leading to excessive summer dryness and temperatures over continental surfaces in the control run is enhanced in the doubled carbon dioxide experiment, resulting in a massive increase in the projected surface temperature. In the high-resolution T106 time-slice scenario experiment performed in this study the global mean latent heat flux and associated intensity of the hydrological cycle is slightly decreased rather than increased with doubled carbon dioxide. A reduction in surface wind speed in the T106 scenario is suggested as a major factor for the reverse of sign. The improved representation of the orography with T106 resolution allows a better estimate of the projected changes of surface energy fluxes in mountain areas, as demonstrated for the European Alps.

Anthropogenic greenhouse forcing and strong water vapor feedback increase temperature in Europe

Europes temperature increases considerably faster than the northern hemisphere average. Detailed month- by-month analyses show temperature and humidity changes for individual months that are similar for all Europe, indicating large- scale weather patterns uniformly influencing temperature. However, superimposed to these changes a strong west- east gradient is observed for all months. The gradual temperature and humidity increases from west to east are not related to circulation but must be due to non- uniform water vapour feedback. Surface radiation measurements in central Europe manifest anthropogenic greenhouse forcing and strong water vapor feedback, enhancing the forcing and temperature rise by about a factor of three. Solar radiation decreases and changing cloud amounts show small net radiative effects. However, high correlation of increasing cloud- free longwave downward radiation with temperature ( r = 0.99) and absolute humidity ( r = 0.89), and high correlation between ERA- 40 integrated water vapor and CRU surface temperature changes ( r = 0.84), demonstrates greenhouse forcing with strong water vapor feedback.

Thermodynamics of a Global-Mean State of the Atmosphere—A State of Maximum Entropy Increase

Abstract Vertical heat transport through thermal convection of the earth’s atmosphere is investigated from a thermodynamic viewpoint. The postulate for convection considered here is that the global-mean state of the atmosphere is stabilized at a state of maximum entropy increase in a whole system through convective transport of sensible and latent heat from the earth’s surface into outer space. Results of an investigation using a simple vertical gray atmosphere show the existence of a unique set of vertical distributions of air temperature and of convective and radiative heat fluxes that represents a state of maximum entropy increase and that resembles the present earth. It is suggested that the global-mean state of the atmospheric convection of the earth, and that of other planets, is stabilized so as to increase entropy in the universe at a possible maximum rate.