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The National Institute of Standards and Technology Advanced Radiometer (NISTAR) onboard the Deep Space Climate Observatory (DSCOVR) provides continuous full-disk global broadband irradiance measurements over most of the sunlit side of the Earth. The three active cavity radiometers measure the total radiant energy from the sunlit side of the Earth in shortwave (SW; 0.2–4 µm), total (0.4–100 µm), and near-infrared (NIR; 0.7–4 µm) channels. The Level 1 NISTAR dataset provides the filtered radiances (the ratio between irradiance and solid angle). To determine the daytime top-of-atmosphere (TOA) shortwave and longwave radiative fluxes, the NISTAR-measured shortwave radiances must be unfiltered first. An unfiltering algorithm was developed for the NISTAR SW and NIR channels using a spectral radiance database calculated for typical Earth scenes. The resulting unfiltered NISTAR radiances are then converted to full-disk daytime SW and LW flux by accounting for the anisotropic characteristics of the Earth-reflected and emitted radiances. The anisotropy factors are determined using scene identifications determined from multiple low-Earth orbit and geostationary satellites as well as the angular distribution models (ADMs) developed using data collected by the Clouds and the Earth's Radiant Energy System (CERES). Global annual daytime mean SW fluxes from NISTAR are about 6 % greater than those from CERES, and both show strong diurnal variations with daily maximum–minimum differences as great as 20 Wm−2 depending on the conditions of the sunlit portion of the Earth. They are also highly correlated, having correlation coefficients of 0.89, indicating that they both capture the diurnal variation. Global annual daytime mean LW fluxes from NISTAR are 3 % greater than those from CERES, but the correlation between them is only about 0.38.

A 44-year (1958-2001) high-resolution atmospheric hindcast for the whole Mediterranean Basin was performed within the EU-funded Hindcast of Dynamic Processes of the Ocean and Coastal Areas of Europe (HIPOCAS) Project. The long-term hindcasted data set, which comprises several atmospheric parameters at different levels, was produced by means of dynamical downscaling from the NCEP/NCAR global reanalysis using the atmospheric limited area model REMO. The REMO hindcast has been exhaustively validated. On that score, various hindcasted surface parameters, such as 10-m wind field, 2-m temperature and mean sea level pressure, have been compared to satellite data (ERS-1/2 scatterometer) and in-situ measurements from offshore stations. In addition, two ocean models (waves and sea level) have been forced with REMO hindcasted fields (mean sea level pressure and 10-m wind field). The validation of these ocean runs, performed through comparisons of simulated waves and sea level with oceanographic measurements, allows to evaluate "indirectly" the quality of the REMO hindcasted data used as atmospheric forcing. Once the quality of the hindcasted data was verified, the efficiency of the regional enhancement performed through dynamical downscaling on the NCEP global reanalysis was assessed. The regional improvement was evaluated through comparisons of REMO and NCEP performance in reproducing observations. The important improvement obtained in the characterization of extreme wind events is particularly remarkable.

Through its interaction with radiation, water vapor provides an important link between the ocean and atmosphere. One way this occurs is through the greenhouse effect; observations of water vapor greenhouse absorption in the Gulf of Mexico during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers— Florida Area Cirrus Experiment during July 2002 are reported here. The quantity dGa/dTs is the change in the amount of upwelling infrared flux absorbed by water vapor as the sea surface temperature increases, and therefore parameterizes the strength of the evaporative feedback between the ocean and atmosphere. Using hemispherical infrared broadband (IRBR) and narrow field of view (NFOV) radiometers aboard a NASA ER-2 aircraft, dGa/dTs was measured during flights on 9 and 26 July marked by large-scale convective and quiescent conditions, respectively. Using the NFOV over the wavelength range 4‐40 mm, dGa/dTs 5 13.4 6 1.0 Wm 22 K21 on 9 July, while on 26 July dGa/dTs 5 9.7 6 0.3 Wm 22 K21. The NFOV measurement of dGa/dTs in the 8‐12-mm wavelength range yielded values of ; 2.5 Wm 22 K21 for both days, indicating that most of the change in greenhouse absorption with increasing ocean temperature occurs in the rotational and vibrational spectral regions of water vapor. The IRBR measurements yielded higher values of dGa/dTs on both days, but were likely affected by cold clouds in the hemispherical radiometer field of view. These results support the link between greenhouse efficiency, mid- to upper-tropospheric water vapor concentration, and convection.

SUMMARY Ozone soundings made inside the Antarctic ozone hole exhibit localized ozone increases within thin layers in the lower stratosphere. These structures, called laminae, are explained as poleward elaments emerging from the vortex edge and transporting relatively ozone-rich air into levels above the geographical site where the sounding equipment has been launched. It is shown that the interior of the Antarctic vortex is not completely isolated with respect to the poleward air mixing. Filament development follows the occurrence of inward breaking near the vortex edge in a region where isentropes are locally uplifted. It is shown that the circulation associated with such uplift may produce the poleward breaking. The role of that circulation is supported by simple barotropic simulations where development of a poleward elament is reproduced in a realistic circular undisturbed vortex.

A quality control process involving outliers processing, homogenization, and interpolation has been applied to 95 monthly precipitation series in the Iberian Peninsula, southern France, and northern Africa during the period 1899–1989. A detailed description of the procedure results is provided and the impact of adjustments on trend estimation is discussed. Outliers have been censored by trimming extreme values. Homogeneity adjustments have been developed by applying the Standard Normal Homogeneity Test in combination with an objective methodology to select reference series. The spatial distribution of outliers indicates that they are due to climate variability rather than measurement errors. After carrying out the homogeneity procedure, 40% of the series were found to be homogeneous, 49.5% became homogeneous after one adjustment, and 9.5% after two adjustments. About 30% of the inhomogeneities could be traced to information in the scarce history files. It is shown that these data present severe h...

The lowest spatial scale at which current climate models are considered to be skillful is on the order of 1000 km because of resolution and computer capabilities. The estimation of the regional changes caused by anthropogenic emissions of greenhouse gases and aerosols therefore is problematic. Here a statistical downscaling scheme is used to study the relationship between large-scale sea level pressure and regional precipitation in southwestern Europe, both in observed data and in outputs from a general circulation model (GCM) forced with increasing levels of greenhouse gases and sulfate aerosols. The results indicate that the GCM does reproduce the main aspects of the large- to local-scale coupled variability. Furthermore, these large- to local-scale relationships remain stable in the scenario simulations. The GCM runs predict increases of advection of oceanic air masses to the Iberian Peninsula that will produce a slight decrease of precipitation amounts in the north coast and the opposite effe...

Pyranometers are reliable, economical radiometers commonly used to measure solar irradiances at the surface in a long-term, monitoring mode. This paper presents a discussion of the response of these instruments to varying environmental conditions, including the magnitude and variability of the irradiance being measured. It is found that different conditions, commonly occurring in field experiments, affect the thermal balance and temperature gradients within the instrument in a variety of ways. Such an effect results in variable offset systematic errors whose origin and magnitude are investigated in laboratory and field experiments. It is shown that these offset errors are proportional to the difference between the fourth power of the dome and detector temperatures, following closely the Stefan–Boltzmann radiation law. Results of field experiments are presented for daytime and nighttime operation over a variety of atmospheric conditions ranging from clear to heavy overcast and rain. All measuremen...

A variety of broadband and spectral surface irradiance measurements from three instrument platforms show significant agreement with one another during three clear sky days (11, 15 and 18 October 1995) during the ARM Enhanced Shortwave Experiment (ARESE). This agreement is only possible when carefully considering absolute and angular calibration issues and applying the recommended correction procedures to the raw signals. By removing systematic measurement errors associated with the various instruments, it is possible to achieve consistencies in the various broadband data sets good to about 1–2% accuracy. It is through these careful comparisons that the measurement techniques currently used in determining downwelling surface flux radiances reflect the highest degree of accuracy and certainty.

We describe a comprehensive set of surface radiative flux measurements made during the Fall 1995 ARM Enhanced Shortwave Experiment (ARESE) at a variety of locations in northern Oklahoma. Accurate measurements of solar spectral broadband (0.224–3.91 μm and 0.68–3.3 μm) and narrow spectral bandpass (10 nm) downwelling irradiances were made over atmospheric conditions ranging from “pristine” clear to heavy overcast. Precise instrument calibrations are used during analyses in deriving absolute downwelling fluxes accurate to about 1% for the broadband and 3% for the spectral instruments. Measured instrument angular responses are incorporated in these analyses to minimize deviations from ideal cosine responses. All calibrated irradiance measurements are available through the ARM ARESE archive via anonymous FTP at ftp.arm.gov and the World Wide Web at www.arm.gov.

With the aim of improving the consistency of terrestrial and atmospheric longwave radiation measurements within the Baseline Surface Radiation Network, five Eppley Precision Infrared Radiometer (PIR) pyrgeometers and one modified Meteorological Research Flight (MRF) pyrgeometer were individually calibrated by 11 specialist laboratories. The round-robin experiment was conducted in a ‘‘blind’’ sense in that the participants had no knowledge of the results of others until the whole series of calibrations had ended. The responsivities C(mV/ Wm 22) determined by 6 of the 11 institutes were within about 2% of the median for all five PIR pyrgeometers. Among the six laboratories, the absolute deviation around the median of the deviations of the five instruments is less than 1%. This small scatter suggests that PIR pyrgeometers were stable at least during the two years of the experiment and that the six different calibration devices reproduce the responsivity C of PIR pyrgeometers consistently and within the precision required for climate applications. The results also suggest that the responsivity C can be determined without simultaneous determination of the dome correction factor k, if the temperature difference between pyrgeometer body and dome is negligible during calibration. For field measurements, however, k has to be precisely known. The calibration of the MRF pyrgeometer, although not performed by all institutes, also showed satisfactory results.

The objectives of the Atmospheric Radiation Measurement (ARM) Enhanced Shortwave Experiment (ARESE) are to directly measure clear and cloudy sky shortwave atmospheric absorption and to quantify any absorption found in excess of model predictions. We undertake detailed model comparisons to near-infrared and total solar flux time series observed by surface and airborne radiometric instruments during the ARESE campaign. Model clear-sky absorption biases generally fall within the range of uncertainty generated by sample size, and assumptions of aerosol properties and surface albedo. Direct measurements by stacked aircraft on the overcast day of October 30, 1995, confirm the detection of enhanced cloud shortwave absorption during ARESE. The detection is substantiated by, and consistent with, three independent measures of cloudy sky absorption estimated in previous studies: cloud forcing ratio, insolation forcing ratio, and albedo/transmission slope. A significant portion of the enhanced absorption occurs at visible wavelengths. Collocated measurements of liquid water path (LWP) suggest the magnitude of the enhanced absorption increases with LWP.

Measurements of downward surface solar radiation (global radiation) and albedo taken during the Central Equatorial Pacific Experiment (CEPEX) are used to obtain baseline estimates for two quantities concerning the radiation budget of the tropical oceans: 1) surface absorption of solar radiation in the central equatorial Pacific under cloud-free conditions, and 2) the corresponding absorption by the atmosphere. These values are then compared to two state-of-the-art radiative transfer models to determine if the models are accurately partitioning solar absorption between the atmosphere and the ocean. The paper develops an independent approach to obtain a clear-sky signal from 10-s resolution surface pyranometer data that is in excellent agreement with upper envelope methods. Over a diurnal average, the ocean absorbs 70.9% ± 1.3% of the solar radiation incident at the top of the atmosphere (TOA). The data, measured from ship and low-flying aircraft platforms, also yield the zenith angle dependence of...

Airborne radiometric measurements were used to determine tropospheric profiles of the clear sky greenhouse effect. At sea surface temperatures (SSTs) larger than 300 kelvin, the clear sky water vapor greenhouse effect was found to increase with SST at a rate of 13 to 15 watts per square meter per kelvin. Satellite measurements of infrared radiances and SSTs indicate that almost 52 percent of the tropical oceans between 20°N and 20°S are affected during all seasons. Current general circulation models suggest that the increase in the clear sky water vapor greenhouse effect with SST may have climatic effects on a planetary scale.

In this paper the authors report results obtained using an unmanned aerospace vehicle (UAV) as an experimental platform for atmospheric radiative transfer research. These are the first ever climate measurements made from a UAV and represent a major step forward in realizing the unique potential of long-endurance, high-altitude UAVs to contribute to climate and environmental studies. Furthermore, the radiative flux divergences determined during these experiments are some of the highest quality measurements of this kind obtained from any type of aircraft and constitute an important test of radiative transfer models.

An algorithm using NOAA-12 AVHRR (Advanced Very High Resolution Radiometer) solar reflectance measurements for retrieving cloud droplet size and optical thickness has been applied to a boundary layer stratocumulus cloud in the vicinity of the Azores on 12 June 1992 during the Atlantic Stratocumulus Transition Experiment (ASTEX). This day was particularly advantageous for validations because of the absence of cirrus or other higher-level clouds during the satellite overpass and the existence of a large relatively uniform stratus cloud dock. Uncertainty estimates for the retrievals are presented along with a discussion of the algorithm. An in-flight absolute calibration of AVHRR channel 1, necessary for accurate optical thickness retrievals, was done concurrently with the retrievals through comparison with a visible radiometer flown on the National Aeronautics and Space Administration's ER-2 and using the stratus cloud as the common reflectance target. Results are compared with in situ microphysica...

The He-broadened half-widths of 65 lines of Phosphine in the range of 2200–2400 cm−1 have been measured at 293 K by means of a Fourier Transform spectrometer at 0. 006 cm−1 resolution. For several experimental conditions related to PH3 and He pressures we used 2 and 5 mm path-length. The broadening coefficients derived using a non-linear fitting technique are reported.

Spectral images of various cloud fields have been made from the ground using a prototype imaging interferometer. The instrument, called DASI (digital array scanned interferometer), is under development as an alternative technique for terrestrial remote sensing. Our paper describes the unusual characteristics of DASI's that make them promising candidates for both ground and aircraft based measurements of clouds. These characteristics include superior signal-to-noise potential, design simplicity and compactness. The prototype DASI had a wavelength sensitivity range of 4550–9090 cm −1 (1.1–2.2 μm), a spectral resolution of 300 cm −1 , a spatial field of view of 5 degrees, and 256 transverse spatial elements for each exposure frame with exposure rates up to 1 frame/s. Spectrally resolved images of cirrus and cumulus clouds over the San Francisco Bay area were obtained by multiple frame scanning over the field of view. The DASI measurements are compared with radiative transfer calculations using LOWTRAN-7. Modification of the LOWTRAN code was necessary so that high spectral resolution data for ice optical properties could be used. With these modifications, the agreement between measured and model results is good in some cases. However, quantitative interpretation of these preliminary measurements was not generally possible because of various sources of uncertainty. Finally, a discussion is given on the potential applications and science yields of DASI instruments in the framework of coordinated field missions such as project FIRE. Such applications include the use of ground and airborne based DASI's to retrieve microphysical properties of clouds and to investigate current problems in atmospheric radiation.

The optical properties of Arctic Haze were studied using a total-direct-diffuse radiometer as part of the Arctic Gas Aerosol Sampling Project, part III (AGASP III). The radiometer was installed on the NOAA WP-3D research aircraft and measured solar downwelling irradiance in seven narrow-band channels in the visible and near-infra-red. Haze optical depths had maximum values near 0.1 in the mid-visible for AGASP flights 310 and 311. An inferred particle size spectrum from flight 311 extinction measurements showed two dominant modes near 0.1 and 0.8 μm. A method of retrieving the angular dependence of scattered radiation is presented and suggests the presence of thin cirrus.

We report the absolute intensities of 38 lines of the Q branch of the v2 band of CH3D near 2200 cm−1, obtained at 98.3 K, using a Fourier Transform spectrometer with a resolution of 0.006 cm−1

Laboratory spectra have been obtained for HNO3 with a Michelson-type Fourier transform interferometer using absorption cells with path lengths of 10.3, 25.5, and 49.8 cm at temperatures of 240, 248, 283, and 294 K. The measurements lead to a total band intensity value of 642 plus or minus 5% per sq cm amagat, which is a temperature independent value after the gas density correction has been made. However, the temperature dependence of the spectral absorption coefficients is apparent in the 885 kayser region.

As a contribution to the climatological characterization of the Izana baseline observatory (Tenerife, Canary Islands, Spain), back-trajectories were calculated and an air mass climatology was developed for a 5-year period. On a daily basis, 5-day back-trajectories were computed for the 850- and 700-HPa levels from January 1983 to December 1987. Trajectories were separated into long- and short-range flows and classified into categories depending on the path followed by the air masses. Flows from the North Atlantic Ocean were much more frequent than flows from continental sectors. In addition, seasonal variations of the sector frequencies were studied and synoptic meteorological patterns were associated with each trajectory category.

Airborne measurements are examined of spectral optical depths, radiative fluxes, and scattered radiation fields during the NASA Caribbean mission (July 7-14, 1991) to characterize the Pinatubo volcanic cloud. The latitudinal and spectral dependence are reported of the volcanic cloud's optical depth. From these measurements moments of the particle-size distribution are determined. The change in planetary albedo induced by the volcanic cloud is calculated for the range of measured optical depths with the objective of assessing the impact on the solar radiation budget. Mid-visible optical depths higher than 0.4 were observed, placing the Pinatubo stratospheric cloud among the thickest ever measured. The latitudinal distribution of extinction shows that by July 7, 1991 the volcanic cloud had extended to 30 deg N. The effective particle radius was determined to be between 0.18 and 0.35 micron with a corresponding columnar mass loading between 35 and 80 mag/sq m.

Infrared radiance measurements were acquired from a narrow-field nadir-viewing radiometer based on the NASA ER-2 aircraft during a coincident Landsat 5 overpass on October 28, 1986 as part of the FIRE Cirrus IFO in the vicinity of Lake Michigan. The spectral bandpasses are 9.90-10.87 microns for the ER-2-based radiometer and 10.40-12.50 microns for the Landsat thematic mapper band. After adjusting for spatial and temporal differences, a comparative study using data from these two instruments is undertaken in order to retrieve cirrus cloud ice-crystal sizes and optical depths. Retrieval is achieved by analysis of measurement correlations between the two spectral bands and comparison to multistream radiative transfer model calculations. The results indicate that the equivalent sphere radii of the cirrus ice crystals were typically less than 30 microns. Such particles were too small to be measured by the available in situ instrumentation. Cloud optical depths at a reference wavelength of 11.4 microns ranged from 0.3 to 2.0 for this case study. Supplemental results in support of this study are described using radiation measurements from the King Air aircraft, which was also in near coincidence with the Landsat overpass.

Two different aspect concerning the state-space modeling for atmospheric pollution are dealt with separately in this paper: (i) the treatment of the advection-diffusion equation and (ii) the use of time series analysis. A method for forecasting the pollutant concentration is proposed. It is based on discretizing the rectified advection-diffusion (RAD) equation by means of a finite-differences scheme and transforming the resultant numerical algorithm into a state-space form. The state-space model uses an optimum estimator algorithm called the Kalman filter to forecast the air pollutant spatial distribution. The state-space modeling defines two basic equations: system state and measurement equations. With regard to the second aspect, state-space methodology is applied to forecast atmospheric aerosol lead (Pb) concentration including wind speed and wind direction as exogenous variables of the models. Data of daily aerosol Pb concentration, wind speed, and wind direction are available for a single si...

Daily wind variability in the Comunidad Foral de Navarra in northern Spain was studied using wind observations at 35 locations to derive subregions with homogeneous temporal variability. Two different methodologies based on principal component analysis were used to regionalize: 1) cluster analysis and 2) the rotation of the selected principal components. Both methodologies produce similar results and lead to regions that are in general agreement with the topographic features of the terrain. The meridional wind variability is similar in all subregions, whereas zonal wind variability is responsible for differences between them. The spectral analysis of wind variability within each subregion reveals a dominant annual cycle and the varying presence of higher-frequency contributions in the subregions. The valley subregions tend to present more variability at high frequencies than do higher-altitude sites. Last, the influence of large-scale dynamics on regional wind variability is explored by studying connections between wind in each subregion and sea level pressure fields. The results of this work contribute to the characterization of wind variability in a complex terrain region and constitute a framework for the validation of mesoscale model wind simulations over the region.

Mesure des intensites de raies absolues de la bande 201-000 de CO 2 a differentes temperatures. Calcul des coefficients de Hermann-Wallis et des moments de transition

The temperature dependence of self-broadened halfwidths of CO2 was studied in the temperature range 165-300 K for the band at 4978/cm. Assuming a power-law of the form gamma(T) = delta(T0)(T0/T)-exp n, the exponent has been determined for J = 6-32. An average value of n = 0.745 + or - 7 percent has been found.

[1] The brightness temperature measurements from the Airborne Imaging Microwave Radiometer (AIMR) microwave radiometer 37 GHz and 90 GHz channels are used to determine the column water vapor amount under clear-sky conditions during the Indian Ocean Experiment (INDOEX) campaign in 1999. The retrieval algorithm is based on the integrated relative humidity profiles measured by numerous dropsondes released from the National Center for Atmospheric Research (NCAR) C-130 aircraft that operated during the 2 month Intensive Field Phase (IFP) of INDOEX. The highest correlations of the linear relationship between the AIMR brightness temperature measurements and the dropsonde column water vapor values are for the nadir brightness temperatures of the 37 GHz and 90 GHz AIMR channels. The column water vapor, w, given with units of kg m−2, may be expressed in terms of the 90 GHz nadir brightness temperature, TB, via the expression, w = −209.4 + 1.025 TB, whereas in terms of the 37 GHz AIMR nadir brightness temperature, w = −277.8 + 1.835 TB. These expressions are valid when AIMR brightness temperature measurements about the NCAR C-130 are made at high altitudes (above 5 km) and when the atmospheric column is cloud-free below the aircraft. Other relationships between the polarized components of the AIMR brightness temperature measurements as well as various combinations (differences) of these polarized components with the column water vapor did not identify any parameterizations to the algorithm better than that seen with the mean of the raw brightness temperature components.

[1] In this paper we report atmospheric radiative forcing, radiative forcing efficiency, and fractional forcing efficiency by aerosols determined from airborne measurements performed during the Indian Ocean Experiment (INDOEX) and the Asian Pacific Regional Characterization Experiment (ACE-Asia). The atmospheric radiative forcing at the surface is calculated in the visible spectral region (400–700 nm) using near-surface observations from the National Center for Atmospheric Research (NCAR) C-130 aircraft. A total-direct-diffuse radiometer (TDDR) with seven spectral bands spanning 400 to 700 nm is used to determine irradiances at the surface as well as spectral (in all seven channels including a narrowband channel at 500 nm, τ500) and broadband (400–700 nm) aerosol optical depths. For INDOEX, using observations in the Arabian Sea, the visible surface forcing efficiencies range from about −74 to −120 W m−2 τ500−1, and the corresponding fractional forcing efficiencies range from about −14 to −30% τ500−1. These forcing values in the Arabian Sea are higher than those derived in a previous study using measurements at a surface site located at the Kaashidhoo Climate Observatory (KCO). During ACE-Asia, the aerosol forcing and forcing efficiency at the surface are slightly lower than those during INDOEX and range from about −54 to −110 W m−2 τ500−1 and −11 to −23% τ500−1, respectively. These values are consistent with similar measurements made at the surface site at Gosan, Jeju, Republic of Korea. Diurnal forcing efficiencies are also estimated for the aircraft measurements giving a range of −23 to −54 W m−2 τ500−1 for INDOEX and −19 to −37 W m−2 τ500−1 for ACE-Asia. Forcing efficiencies are determined using broadband aerosol optical depths and reflect small differences (related to changing aerosol characteristics) relative to those values obtained using narrowband quantities.

[1] Column aerosol optical depth (AOD) and surface shortwave irradiance (SSI) measurements relevant to computation of the aerosol surface radiative forcing (ΔF) and forcing efficiency (β) were taken as part of Aerosol Characterization Experiment-Asia (ACE-Asia) at the Gosan surface site in Korea in April 2001. We compare the AOD and SSI derived from three different types of Sun photometers and three sets of radiometers. We also estimate the ΔF and β using two methods and quantify the observational uncertainties of these parameters. A comparison of the AOD at 500 nm shows that the three Sun photometers generally agreed within 0.014 (mean), 0.0142 (bias), and 0.0298 (root mean square) for coincident observations. Over the course of the comparison, the mean differences between the SSI measurements were 1.6, 11.7, and 10.1 Wm−2 for direct, diffuse and global irradiances, respectively. However, for both the AOD and the SSI comparisons, relatively high instantaneous differences between the instruments were apparent on days with heavy dust at the surface. The mean β and associated deviations, which were estimated by the combinations of different instrument-derived AODs and SSIs, for simultaneous observation data at a 60° solar zenith angle are −79.50 ± 3.92 and −82.57 ± 5.70 Wm−2/τ500 for globalshaded (sum of direct and diffuse irradiances) and globalunshaded (measured by the unshaded pyranometer) irradiances, respectively. The uncertainties in β associated with uncertainties in the AOD and SSI (in parentheses) for globalshaded and globalunshaded irradiance are about 8.6% and 3.2% (10.7%), respectively. A 2% difference between the measured global irradiances for a given 9 days was translated into an uncertainty of 19% in ΔF. This difference in ΔF between instruments caused a 14% deviation in β.

[1] Aerosol particles affect the global energy budget and Earth's climate through the absorption and scattering of both solar and terrestrial radiation. Here we present a study of column-averaged aerosol optical properties derived from clear-sky measurements of the direct and diffuse components of the solar downwelling spectral and broadband irradiance during a 10-day observation period at the Atmospheric Radiation Measurement (ARM) facility in central Oklahoma in the fall of 2001. Using a radiative transfer model and Mie calculations of the optical properties of standard continental aerosol components and assuming a constant aerosol composition with altitude, we determine the phenomenological aerosol model that best fits both the direct and diffuse spectral irradiances. Internal and external homogeneous aerosol mixtures were considered, along with single-aerosol and coated sphere models. We find that the irradiance data is well fit statistically by at least one of the models for every clear-sky time considered during the observations period, with no excess gaseous absorption required to fit the data. By far the best fitting model consisted of ultrafine (∼5–30 nm radius) coated spheres with absorbing black carbon cores and nonabsorbing shells of water or a similar substance. The mean value of the 500-nm aerosol single-scattering albedos for the entire 10-day period was 0.76. These results indicate that absorbing carbonaceous aerosols can have a significant radiative impact even in rural settings.

The spatial patterns of surface air-temperature variations in the period 1000 to 2100, simulated with the ECHO-G atmosphere-ocean coupled model, are analyzed. The model was driven by solar, volcanic and greenhouse gas forcing. The leading mode of temperature variability in the preindustrial period represents an almost global coherent variation of temperatures, with larger amplitudes over the continents and Northern Hemisphere. This mode also describes a large part of the spatial structure of the warming simulated in the 21st century. However, in the 21st century, regional departures from this spatial structure are also present and can be ascribed to atmospheric circulation responses to anthropogenic forcing in the last decades of the 21st century.

This technical comment responds to an article on absorption of radiation by clouds. Measurement of atmospheric absorption is difficult, requiring measurement of all radiation flowing into and from a volumn. In measurement from aircraft the volume is ill defined and measurement of fluxes on its boundaries is limited to a few locations. In the sited study the cloud flux data derive from satellite observations where as the surface measurement are obtained from either a single radiometer or a network of 11 radiometers. This analysis is supposed to account for large space and time scale variability and accomodate undersampled boundary fluxes. However, the commentor contends that the report contains neither an error analysis or evidence to support the assumption. 24 refs., 2 figs.

[1] As a follow-on to the Atmospheric Radiation Measurement (ARM) Enhanced Shortwave Experiment (ARESE) I, which provided atmospheric shortwave measurements from collocated aircraft, ARESE II performed similar measurements with a single aircraft flying at an altitude of 7 km over an instrumented surface site. ARESE I and ARESE II absorptance measurements are found to agree with each other and, when converted to top of the atmosphere (TOA) instantaneous column absorption, are also consistent with GOES 8 and Scanner for Radiation Budget (ScaRaB) satellite observations. Measurements are compared to calculations performed with five different radiative transfer models. It is found that the calculated absorption differs systematically from the observations in cloudy conditions, with models underpredicting the absorption. In particular, all the models tested here underpredict the measured instantaneous cloudy column absorption by amounts ranging from 17 to 61 W m−2, depending on the models and cases studied. The various models, using identical input, differ among themselves; for example, for the same cloudy case, absorptance estimates range from 0.22 to 0.27 for the atmospheric column from the surface to the TOA. It is also found that model-calculated absorptances appear not as well correlated to cloud optical depth variations as the measured absorptances appear to be. Measured and calculated clear-sky absorptances agree well within the uncertainties. Cloudy-sky absorptances in the visible spectral region (300 to 700 nm) reach values of as much as 0.02 during ARESE II while the equivalent measurements for ARESE I range around 0.06. This visible absorptance may be related to aerosols and their day-to-day and seasonal variability.

4.8 W m � 2 /t500 for the total solar, near-infrared, and visible spectral regions. We also introduce a new radiative forcing parameter, the fractional forcing efficiency, defined to express the radiative forcing relative to the total energy incident at the top of the atmosphere. The fractional diurnal forcing efficiency at Gosan during ACE-Asia was � 18.0 ± 2.3, � 16.2 ± 2.4, and � 26.7 ± 3.3%/t500 for the same band passes, indicating that a larger percentage of the flux at visible wavelengths is radiatively forced compared to the total and near-infrared portions of the solar spectrum. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 0394 Atmospheric Composition and Structure: Instruments and techniques; KEYWORDS: radiative fluxes, radiative forcing, aerosols

[1] We describe a radiation experiment performed at the Kaashidhoo Climate Observatory (KCO), Republic of Maldives, during the Indian Ocean Experiment (INDOEX) field campaign in February through March 1999. Both the total solar broadband (0.3 to 3.81 μm) and visible spectral narrowband (seven spectral channels in the region from 0.4 to 0.7 μm) quantities were measured for the total (hemispherical), direct solar, and diffuse (including forward scattering) components of the radiation field. The aerosol optical depth at 500 nm, obtained from one of the narrrowband spectral channels, ranged from approximately 0.2 to 0.7 during the period encompassing the intensive field phase (IFP) of INDOEX. The diurnally averaged atmospheric forcing efficiencies determined for the total solar broadband and visible spectrum are −72.2 ± 5.5 W m−2 and −38.5 ± 4.0 W m−2, respectively. Model simulations driven by in situ measurements and realistic aerosol optical properties infer a single scattering albedo of 0.874 ± 0.028 at 500 nm.

[1] The second ARM (Atmospheric Radiation Measurement) Enhanced Shortwave Experiment (ARESE II) used a single aircraft flying above the north central Oklahoma Southern Great Plains ARM central facility to measure the atmospheric absorption in the column of air between the surface and the Twin Otter altitude ceiling around 7 km on both clear and overcast days. For this experiment, three types of broadband radiometers were used to measure upwelling and downwelling shortwave flux on the aircraft at 7 km. This provided redundancy that was lacking in the first ARESE. Further, all instruments used on the ground and on the aircraft were calibrated on the ground against the same radiation standard. Preflight and postflight comparisons of the broadband instruments used on the aircraft during the flight series with the standard, and comparisons of the ground instruments with the standard during the flights, suggest agreement much better than the target uncertainty of 20 W/m2 at the 95% confidence level. Comparisons of the standard and the aircraft instruments for low-altitude passes on clear days indicate more uncertainty as expected for a nonstationary platform. The estimated uncertainty in the measured column absorption based on the difference in measured net irradiances at the surface and near 7 km at the 95% confidence level is 20 W/m2.

This paper describes the simulation of the earth radiation budget (ERB) as viewed by Triana and the development of correction models for converting Triana-viewed radiances in to a complete ERB. A full range of Triana views and global radiation fields are simulated using data from the Earth Radiation Budget Experiment (ERBE) and analyzed with a set of empirical correction factors specific to the Triana views. The results show that the accuracy of global correction factors to estimate ERB from Triana radiances is a function of the Triana position from Lagrange-1 (L1) or the Sun position. Spectral analysis of the global correction factor indicates that both shortwave (SW) and longwave (LW) parameters undergo seasonal and diurnal cycles that dominate the periodic fluctuations. The diurnal cycle, especially its amplitude, is also strongly dependent on the seasonal cycle. Based on these results, models are developed to correct the radiances for unviewed areas and anisotropic emission and reflection. A preliminary assessment indicates that these correction models can be applied to Triana radiances to produce the most accurate global ERB to date.

International audience; Every year, from December to April, anthropogenic haze spreads over most of the North Indian Ocean, and South and Southeast Asia. The Indian Ocean Experiment (INDOEX) documented this Indo-Asian haze at scales ranging from individual particles to its contribution to the regional climate forcing. This study integrates the multiplatform observations (satellites, aircraft, ships, surface stations, and balloons) with one-and four-dimensional models to derive the regional aerosol forcing resulting from the direct, the semidirect and the two indirect effects. The haze particles consisted of several inorganic and carbonaceous species, including absorbing black carbon clusters, fly ash, and mineral dust. The most striking result was the large loading of aerosols over most of the South Asian region and the North Indian Ocean. The January to March 1999 visible optical depths were about 0.5 over most of the continent and reached values as large as 0.2 over the equatorial Indian ocean due to long-range transport. The aerosol layer extended as high as 3 km. Black carbon contributed about 14% to the fine particle mass and 11% to the visible optical depth. The single-scattering albedo estimated by several independent methods was consistently around 0.9 both inland and over the open ocean. Anthropogenic sources contributed as much as 80% (_+10%) to the aerosol loading and the optical depth. The in situ data, which clearly support the existence of the first indirect effect (increased aerosol concentration producing more cloud drops with smaller effective radii), are used to develop a composite indirect effect scheme. The Indo-Asian aerosols impact the radiative forcing through a complex set of heating (positive forcing) and cooling (negative forcing) processes. Clouds and black carbon emerge as the major players. The dominant factor, however, is the large negative forcing (-20 +_ 4 W m-t) at the surface and the comparably large atmospheric heating. Regionally, the absorbing haze decreased the surface solar radiation by an amount comparable to 50% of the total ocean heat flux and nearly doubled the lower tropospheric solar heating. We demonstrate with a general circulation model how this additional heating significantly perturbs the tropical rainfall patterns and the hydrological cycle with implications to global climate.

We have extended the interpretations made in two prior studies of the aircraft shortwave radiation measurements that were obtained as part of the Atmospheric Radiation Measurements (ARM) Enhanced Shortwave Experiment (ARESE). These extended interpretations use the 500 nm (10 nm bandwidth) measurements to minimize sampling errors in the broadband measurements. It is indicated that the clouds present during this experiment absorb more shortwave radiation than predicted by clear skies and thus by theoretical models, that at least some (≤20%) of this enhanced cloud absorption occurs at wavelengths

The title of Science 's article about NASA's decision to cancel the Deep Space Climate Observatory (DSCOVR) satellite mission, “NASA terminates Gore's eye on Earth” (ScienceScope, A. Lawler, 6 Jan., p. 26), was misleading. This title trivializes the real nature of the mission and obscures the fact that DSCOVR is not the same as the Triana mission promoted by then Vice President Gore. The Triana concept was to provide the public (via the Internet) with a continuous, real-time image of the entire, sunlit Earth, essentially a TV camera in space. DSCOVR is a high-priority, peer-reviewed scientific mission, conceived and developed by a team of experts. In 1998, NASA issued a request for information to the science community regarding utilization of the L-1 Lagrange point between Earth and the Sun, from which the entire sunlit hemisphere of our planet can be continuously observed. Our team responded by recommending broadband and high-resolution, spectro-radiometric measurements that would improve understanding of the solar/infrared energy balance ([1][1]) for the Earth system as well as of atmospheric composition and dynamics. Importantly, these observations would provide calibrations and integral constraints for all satellites in geostationary and low Earth orbit because they all are at times in view from L-1. Our proposal was selected by NASA after rigorous scientific and technical reviews. Solar activity observations were added at NASA's request to satisfy scientific needs and NOAA's operational requirements for space weather monitoring. DSCOVR is firmly based on the ideas developed by the science team. The transmission of live images of Earth added to the educational outreach component of the mission but was by no means the primary objective. Many scientists, both in the United States and abroad, view DSCOVR as one of NASA's most important and innovative Earth science missions. The satellite has been built and could still be launched in time to provide synergistic data coincident with current and future orbiting systems. It offers great potential both as a source of fundamental scientific observations and as a pioneering Earth sciences mission from deep space. 1. 1.[↵][2]1. R. J. Charlson, 2. F. P. J. Valero, 3. J. H. Seinfeld , Science 308, 806 (2005). [OpenUrl][3][Abstract/FREE Full Text][4] [1]: #ref-1 [2]: #xref-ref-1-1 "View reference 1. in text" [3]: {openurl}?query=rft.jtitle%253DScience%26rft.stitle%253DScience%26rft.aulast%253DCharlson%26rft.auinit1%253DR.%2BJ.%26rft.volume%253D308%26rft.issue%253D5723%26rft.spage%253D806%26rft.epage%253D807%26rft.atitle%253DATMOSPHERIC%2BSCIENCE%253A%2BIn%2BSearch%2Bof%2BBalance%26rft_id%253Dinfo%253Adoi%252F10.1126%252Fscience.1108162%26rft_id%253Dinfo%253Apmid%252F15879202%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [4]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6Mzoic2NpIjtzOjU6InJlc2lkIjtzOjEyOiIzMDgvNTcyMy84MDYiO3M6NDoiYXRvbSI7czoyNDoiL3NjaS8zMTEvNTc2Mi83NzUuMy5hdG9tIjt9czo4OiJmcmFnbWVudCI7czowOiIiO30=

The climate of Earth and its global mean surface temperature are the consequence of a balance between the amount of solar radiation absorbed by Earth's surface and atmosphere and the amount of outgoing longwave radiation emitted by the system. The former is governed by the albedo (reflectivity) of the system, whereas the latter depends strongly on the atmospheric content of gases and particles (such as clouds and dust). Although the theory of absorption of infrared radiation by gases in the atmosphere (1) is well accepted and embodied in climate models, the observational and theoretical treatments of albedo, aerosols, and clouds are still under development. One brevium (2) and two reports (3, 4) in this issue report estimates of Earth's albedo and of solar radiation reaching the surface, but the uncertainties remain large. The buildup of CO_2 (5), CH_4, and other greenhouse gases during the past century has led to an increased absorption of infrared radiation in the atmosphere (enhanced greenhouse effect) and a consequent warming (“positive forcing”) of the climate. But human-made changes in aerosols and clouds can cause enhanced albedo and hence cooling (“negative forcing”), and they may already have offset a substantial part of the enhanced greenhouse effect. Present trends suggest that by 2050, the magnitude of the enhanced greenhouse effect will be so large that the net anthropogenic forcing will be unequivocally positive and substantial in magnitude (6).

In their Letter “Have clouds darkened since 1995?” (14 Nov. 2003, p. [1151][1]), Z. Li and colleagues discuss points raised in an earlier news article on climate models and clouds (“Making clouds darker sharpens cloudy climate models,” R. A. Kerr, News of the Week, 20 June 2003, p. [1859][2

Aircraft measurements of solar flux in the cloudy tropical atmosphere reveal that solar absorption by clouds is anomalously large when compared to theoretical estimates. The ratio of cloud forcing at an altitude of 20 kilometers to that at the surface is 1.58 rather than 1.0, as predicted by models. These results were derived from a cloud radiation experiment in which identical instrumentation was deployed on coordinated stacked aircraft. These findings indicate a significant difference between measurements and theory and imply that the interaction between clouds and solar radiation is poorly understood.