Atsumu Ohmura

ETH Zurich | ETH Zürich · Institute of Atmosphere and Climate Science

Rising anthropogenic greenhouse gases, such as CO2, CH4, N2O and others, are known to absorb and emit terrestrial thermal radiation back to the Earth's surface, leading to radiative forcing and rising surface temperatures. Nonetheless, radiation measurements now show that the rapid increase in temperature over continents since the end of the last c...

Despite the importance of high-latitude surface energy budgets (SEBs) for land-climate interactions in the rapidly changing Arctic, uncertainties in their prediction persist. Here, we harmonize SEB observations across a network of vegetated and glaciated sites at circumpolar scale (1994–2021). Our variance-partitioning analysis identifies vegetatio...

Solar variability has been hypothesized to be a major driver of North Atlantic millennial-scale climate variations through the Holocene along with orbitally induced insolation change. However, another important climate driver, volcanic forcing has generally been underestimated prior to the past 2,500 years partly owing to the lack of proper proxy t...

The Global Energy BalanceArchive (GEBA) is a database for the worldwide measured energy fluxes at the Earth’s surface. GEBA is maintained at ETH Zurich (Switzerland) and has been founded in the 1980s by Prof. Atsumu Ohmura. It has continuously been updated and currently contains around 2500 stations with 500‘000 monthly mean entries of various surf...

The status of the cryosphere at the end of the 20th century is presented with respect to their relationships to climate. Firstly, the physical condition of the earth's surface is analysed to understand how the earth alone among all planets has a favourable condition for the existence of water in all phases. Then the distributions of the four main c...

There is growing evidence that the rate of warming is amplified with elevation, such that high-mountain environments experience more rapid changes in temperature than environments at lower elevations. Elevation-dependent warming (EDW) can accelerate the rate of change in mountain ecosystems, cryospheric systems, hydrological regimes and biodiversit...

The Rhone Glacier is the best-documented case in the Alps of a rapidly retreating glacier. Photographs and other documents show the history of the changing glacier since the Little Ice Age. Fluctuations of the glacier tongue reflect decadal temperature fluctuations during the observation period. The last quarter century witnessed the most spectacul...

Energy balance climatology emerged from the 19th century thermodynamics and radiation research. Energy balance consideration offered an attractive intellectual ground to apply the conservation principle to a natural process. The climate system was often compared to the processes in a steam engine. Research into this field started with insufficient...

We present the results of continuous longwave downwelling irradiance (LDI) monitoring in Moscow from April 2008 to March 2012, which has been in operation at the Meteorological Observatory of Moscow State University (MSU MO). The measurements are carried out within wavelength range 3.5-50 μm using a precision infrared radiometer (PIR) which is regu...

In the present article, monthly mean temperature at 56 stations assembled in 18 regional groups in 10 major mountain ranges of the world were investigated. The periods of the analysis covered the last 50 to 110 years. The author found that the variability of temperature in climatic time scale tends to increase with altitude in about 65 % of the reg...

The total solar irradiance (TSI, or solar constant) acquired a new value: 1361 W m−2 instead of 1365 W m−2. However a long-term variation of TSI was not detected. The solar irradiance at the earth's surface is considerably smaller (170 W m−2) than previously believed (e.g. 198 W m−2 of IPCC AR4). The previous overestimation is due to the underestim...

Glacier mass balance and secular changes in mountain glaciers and ice caps are evaluated from the annual net balance of 137 glaciers from 17 glacierized regions of the world. Further, the winter and summer balances for 35 glaciers in 11 glacierized regions are analyzed. The global means are calculated by weighting glacier and regional surface areas...

Annual precipitation, evaporation, and calculated accumulation from reanalysis model outputs have been investigated for the Greenland Ice Sheet (GrIS), based on the common period of 1989–2001. The ERA-40 and ERA-interim reanalysis data showed better agreement with observations than do NCEP-1 and NCEP-2 reanalyses. Further, ERA-interim showed the cl...

No abstract available.

The integrity of the Baseline Surface Radiation Network (BSRN) radiation monthly averages are assessed by investigating the impact on monthly means due to the frequency of data gaps caused by missing or discarded high time resolution data. The monthly statistics, especially means, are considered to be important and useful values for climate researc...

The integrity of the Baseline Surface Radiation Network (BSRN) radiation monthly averages are assessed by investigating the impact on monthly means due to the frequency of data gaps caused by missing or discarded high time resolution data. The monthly statistics, especially means, are considered to be important and useful values for climate researc...

Observations indicate that greenhouse induced 20th century warming has been strongly modulated by variations in surface solar radiation. Between the 1950s and 1980s declining surface solar radiation ("global dimming") likely caused a dampening of global warming, whereas increasing surface solar radiation ("brightening") may have contributed to the...

An inventory of the surface area and volume of the world's glaciers, outside Greenland and Antarctica, was part of the International Hydrological Decade (1965–74). It was considered essential to an understanding of the role played by glaciers in the hydrological cycle and was to be repeated every 50 years to detect change. To date, 46% of the estim...

Modern geoinformatic techniques allow the automated creation of detailed glacier inventory data from glacier outlines and digital terrain models (DTMs). Once glacier entities are defined and an appropriate DTM is available, several methods exist to derive the inventory data (e.g. minimum, maximum and mean elevation; mean slope and aspect) for each...

Long-term records of surface radiation measurements indicate a decrease in the solar radiation between the 1950s and 1980s (``global dimming''), then its recovery afterward (``global brightening'') at many locations all over the globe [Wild, 2009]. On the other hand, the global brightening is delayed over the Asian region [Ohmura, 2009]. It is sugg...

A 94-year time series of annual glacier melt at four high elevation sites in the European Alps is used to investigate the effect of global dimming and brightening of solar radiation on glacier mass balance. Snow and ice melt was stronger in the 1940s than in recent years, in spite of significantly higher air temperatures in the present decade. An i...

This study investigates the recent variations in surface solar radiation inferred from a comprehensive set of ground-based observational records updated to 2005. Surface radiation data beyond 2000 are thereby particularly interesting, as they can provide independent and complementary information to the ambitious satellite programs which became oper...

Decadal changes in shortwave irradiance at the Earth's surface are estimated for the period from approximately 1960 through to 2000 from pyranometer records stored in the Global Energy Balance Archive. For this observational period, estimates could be calculated for a total of 140 cells of the International Satellite Cloud Climatology Project grid...

Long-term variations of global solar irradiance at the Earth?s surface from the beginning of the observations to 2005 are analyzed for more than 400 sites. Further, likely causes for the variations, an estimation of the magnitudes of aerosol direct and indirect effects, and the temperature sensitivity of the climate system due to radiation changes...

The surface solar radiation (SSR) is an important factor influencing the local and global energy budget. However, information on the spatial and temporal variation of SSR is limited. A more commonly available measure, which may provide such information, is the diurnal temperature range (DTR). In this study we analyze the relationship between DTR an...

concentrations and aerosols have major impacts on the land energy and water cycles, and in particular on evapotranspiration (ET). Here we analyze how the main external drivers of ET (incident solar radiation and precipitation) vary regionally, using recent data from a eddy-covariance flux tower network (FLUXNET) and a multi-model re-analysis (GSWP-...

The Nobel Peace Prize awarded to the Intergovernmental Panel on Climate Change (IPCC) and former U.S. vice president Al Gore indicates that global warming is recognized as a real phenomenon critical to human beings. However, humanity's knowledge concerning global warming is based on an uncertainty larger than 50% in the warming rate during the past...

It has been widely accepted that diurnal temperature range (DTR) decreased on a global scale during the second half of the twentieth century. Here we show however, that the long-term trend of annual DTR has reversed from a decrease to an increase during the 1970s in Western Europe and during the 1980s in Eastern Europe. The analysis is based on the...

The influence of snow microstructure on thermal and radiative transfer in snow has not been thoroughly investigated as the tools necessary to efficiently measure microstructural geometry at millimeter resolution have not yet been available. Here we investigate the impact of snow microstructure on the thermal and radiative properties of snow and spe...

Radiative transfer model calculations of solar fluxes during cloud-free periods often show considerable discrepancies with surface radiation observations. Many efforts have been undertaken to explain the differences between modeled and observed shortwave downward radiation (SDR). In this study, MODTRAN4v3r1TM (designed later simply as MODTRANTM) wa...

1] The rapid temperature increase of 1°C over mainland Europe since 1980 is considerably larger than the temperature rise expected from anthropogenic greenhouse gas increases. Here we present aerosol optical depth measurements from six specific locations and surface irradiance measurements from a large number of radiation sites in Northern Germany...

Clouds represent a major source of uncertainty in understanding climate change, because potential changes in the way they affect the atmospheric and surface energy budget are difficult to predict. It is therefore important to determine how clouds affect radiation. Stratiform clouds in particular have an important effect on climate as they cover lar...

We study the feasibility of deriving historical TSI (Total Solar Irradiance) from lunar borehole temperatures. As the Moon lacks Earth's dynamic features, lunar borehole temperatures are primarily driven by solar forcing. Using Apollo observed lunar regolith properties, we computed present-day lunar regolith temperature profiles for lunar tropical,...

1] An analysis of satellite and surface measurements of aerosol optical depth suggests that global average of aerosol optical depth has been recently decreasing at the rate of around 0.0014/a. This decrease is nonuniform with the fastest decrease observed over the United States and Europe. The observed rate of decreasing aerosol optical depth produ...

The effect of climate change in the 20th century is investigated based on measured mass-balance data. Annual, winter and summer mass balances on Claridenfirn, Switzerland, (since 1914/15) Storglaciären, Sweden, (since 1945/46) Storbreen, Norway, (since 1948/49) Glacier de Sarennes, France, (since 1948/49) and Vernagtferner, Austria, (since 1965/66)...

Longwave radiative flux divergence within the lowest 50 m of the atmospheric boundary layer was observed during the Eidgenössische Technische Hochschule (ETH) Greenland Summit experiment. The dataset collected at 72°35′N, 38°30′W, 3203 m MSL is based on longwave radiation measurements at 2 and 48 m that are corrected for the influence of the suppor...

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 radi...

Speculations on the impact of variations in surface solar radiation on global warming range from concerns that solar dimming has largely masked the full magnitude of greenhouse warming, to claims that the recent reversal from solar dimming to brightening rather than the greenhouse effect was responsible for the observed warming. To disentangle surf...

Atmospheric water vapor and surface humidity strongly influence the radiation budget at the Earth's surface. Water vapor not only absorbs solar radiation in the atmosphere, but as the most important greenhouse gas it also largely absorbs terrestrial longwave radiation and emits part of it back to the surface. Using surface observations, like longwa...

The Moon is an ideal place to reconstruct historical total solar irradiance (TSI). With undisturbed lunar surface albedo and the very low thermal diffusivity of lunar regolith, changes in solar input lead to changes in lunar surface temperature that diffuse downward to be recorded in the temperature profile in the near-surface layer. Using regolith...

Yafeng Shi, ed. 2006. The Quaternary glaciations and environmental variations in China. Shijiazhuang, Hebei Science and Technology Publishing House. 618pp. ISBN 7 5375 3247 8, hardback. 190.00 yuan. - Volume 53 Issue 182 - Atsumu Ohmura

Snow cover fraction (SCF) has a significant influence on the surface albedo and thus on the radiation balance and surface climate. Long-term three dimensional simulations with General Circulation Models (GCMs) showed that the SCF greatly affects the climate in the Northern Hemisphere. By means of both ground observations and remotely sensed data, s...

Hemispherical directional reflectance factors (HDRF) were collected under solar zenith angles from 49° to 85°. The experimental site was the Greenland Summit Environmental Observatory (72°35'N, 34°30'W, 3203 m above sea level) where both the snow and the atmosphere are very clean. The observations were carried out for two prevailing snow surface ty...

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...

The global mass balance of the glaciers outside Greenland and Antarctica is evaluated based on long-term mass-balance observations on 75 glaciers. The cause of the mass-balance change is investigated by examining winter and summer balances from 34 glaciers. The main finding is a common development in mass-balance changes shared by a number of glaci...

The variation of global radiation (sum of direct solar and diffuse sky radiation) at the Earth’s surface is examined based on pyranometer measurements at about 400~sites. The period of the study covers in general the last 50 years. For Europe the study is extended to the beginning of observations in the 1920s and 1930s. Global radiation generally i...

The earth's energy and water balances are summarised with the most recent observational and computational results. A special reference is given to the earth's surface. After a brief discussion of the limits of the observational accuracy, the author explains the mean state of the energy balance starting with the sun, through the atmosphere and to th...

This work presents a new field goniospectrometer developed at the Institute for Atmospheric and Climate Science (IAC) of the Swiss Federal Institute of Technology (ETH; Switzerland). The goniospectrometer was built to study the hemispherical directional reflectance factor (HDRF) of snow, but can also be applied to other surfaces with moderate surfa...

Pyranometer measurements and two satellite-derived data sets were used to evaluate surface downward shortwave irradiance over China. Compared to pyranometer measurements, the satellite-derived data overestimated surface shortwave irradiance, particularly over large cities. These positive biases can be attributed to aerosols with absorptive properti...

Solar fluxes at the Earth’s surface calculated in General Circulation Models (GCMs) contain large uncertainties, not only in the presence of clouds, but, as shown here, even under cloud-free (i.e. clear-sky) conditions. Adequate observations to constrain these clear-sky fluxes at the surface have long been missing. The present study provides newly...

A new global energy (heat) balance is presented, based on a composite database of surface measurements, satellite-based observations and GCM computations. The present picture differs greatly from its predecessors in larger atmospheric absorption of solar radiation, smaller global radiation at the earth's surface and larger terrestrial (longwave) at...

The variation of global radiation (sum of direct solar and diffuse sky radiation) at the Earth’s surface is examined based on pyranometer measurements at about 400 sites. The period of the study covers in general the last 50 years. For Europe the study is extended to the beginning of observations in the 1920s and 1930s. Global radiation generally i...

The chemistry-climate model SOCOL has been applied for the study of ozone and temperature anomalies during 1979–1993. Temperature and ozone anomalies have been obtained for a set of model runs forced by all major stratospheric forcing mechanisms. Forcings have been prescribed separately and together to assess their individual influence on stratosph...

Recent evidence suggests that the amount of solar radiation reaching the earth surface is not stable over time but exhibits significant decadal variations. These variations, in addition to the changes in thermal radiation induced by alterations in greenhouse gases, cause changes in radiative forcings which may significantly affect surface climate....

Europe's 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 gr...

Consistent and validated data sets of satellite‐borne radiances and of a large variety of products describing the characteristics of terrestrial cloud and radiation fields have been produced within the International Satellite Cloud Climatology Project (ISCCP) covering the years 1983 through to 2003. A subset (annual and seasonal averages of the 5 y...

Variations in solar radiation incident at Earth's surface profoundly affect the human and terrestrial environment. A decline in solar radiation at land surfaces has become apparent in many observational records up to 1990, a phenomenon known as global dimming. Newly available surface observations from 1990 to the present, primarily from the Norther...

Differences between computed and observed cloud-free longwave downward radiation (LDR) were examined both for Payerne and six further radiation sites of the Alpine Surface Radiation Budget (ASRB) network. LDR was computed by the complex radiative transfer model (RTM) MODTRAN v4.0 and by a simplified RTM used in the numerical weather prediction mode...

We have carried out a set of transient runs of the Chemistry-Climate Model SOCOL covering 1975-2000 driven by time evolving sea surface temperature and sea ice distributions, sulfate aerosol loading, spectral solar irradiance, greenhouse gases and ozone destroying substances. We present the solar signal in the atmosphere extracted from these transi...

This document is part of Volume 6 'Observed Global Climate' of Landolt-Börnstein - Group V Geophysics. 4 Radiation budget of the climate system (Part 1/5) 4.1 Introduction and conventions 4.2 Radiative transfer in the atmosphere 4.3 An overview on the radiation budget of the climate system 4.3.1 Annual budget 4.3.2 Solar radiation 4.3.3 Radiation b...