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Balloon-based soundings have been carried out for more than 100 years and have since formed an important database and reference for characterizing the 3-dimensional structure of the atmosphere. In addition to the meteorological standard variables trace gases, aerosol and radiation profiles have recently also been recorded using radiosondes.Since this is significantly more expensive equipment compared to a standard radiosonde, some more effort is required to enable safe soundings and transfer back home for each case. The repetition rates of the soundings are consequently much lower than those of the operational measurements.The measurement conditions during the sounding differ significantly from the usual conditions for radiation measurements near the ground: temperatures down to -85°C at the tropopause level, rapid temperature changes of more than 50 K/h at an ascent rate of 5 m/s and possible impacts of liquid and iced cloud droplets on the observations need to be handled. This requires adjustments to the acquisition of measured values ​​and a careful selection of the launch time.At Lindenberg Meteorological Observatory (52.21° north, 14.12° east) of the German Weather Service, a total of 68 all-season sounding flights have been carried out since April 2015 with modified radiosondes of the Meteolabor SRS-C34 and SRS-C50 type with added upward and downward solar and terrestrial radiation.This presentation is discussing and interpreting the observational results of individual cloudless cases as well as soundings passing low, medium and high clouds. The downward fluxes are significantly modified below the tropopause. On the other hand, reflected radiation and terrestrial radiation are not only subject to local changes, even up to an altitude of 34 km, which can be quantified by including data on land use and cloud cover.In addition, we will show the result of a case study where the radiative fluxes observed in and around clouds are used to validate corresponding numerical simulations performed with the ICON-ART model.

Solar shortwave and terrestrial thermal longwave irradiance are measured at radiation sites at the Earth's surface and on satellite platforms high up in space, since many years. Radiation profiles through the Earth's atmosphere, however, have only sporadically been measured from enhanced upper-air radiosondes. Here we show profiles of solar and terrestrial radiation measured with balloon-borne radiometers through cloud-free and cloudy atmospheres, which reveal radiative effects of temperature, water vapor, ozone and clouds on downward and upward radiation. Shortwave radiation profiles show solar absorption in the free atmosphere and strong reflection in clouds and albedo effects on the ground and the atmosphere above. Longwave upward radiation profiles visualize terrestrial radiation emitted from the Earth's surface, which is partly absorbed and reemitted in the boundary layer and in the atmosphere by water vapor and other greenhouse gases. Longwave downward radiation profiles show the absorbed terrestrial radiation in the atmosphere and reveal the warming effect of increasing greenhouse gases, and by this visualize and demonstrate radiative forcing and a changing greenhouse effect by water vapor in the Earth's atmosphere. Longwave net radiation profiles show terrestrial emission into space to be reduced by water vapor and clouds. Measured radiation profiles are compared to numerically calculated radiation profiles.

Networks of atmospheric measuring techniques are fundamental to ensuring the scientific and climatologic usefulness of atmospheric measurements. Because air masses can move hundreds of kilometers every day, weather, air pollution, and climate are international issues—they cannot be addressed at the national level alone. However, measurement stations and systems are usually operated and funded at the national level or at even more local levels. To ensure that results are comparable and to address global problems, it is therefore crucial to coordinate goals, operating procedures, stations, systems, standards, traceability, etc. at the international level. International networks allow the implementation of different atmospheric measuring techniques at specifically selected sites and are relevant to all stages of the generation of atmospheric data on physical properties and chemical compositions. The purpose of this chapter is to introduce and describe the history, structure, instruments, methods, and other aspects of these atmospheric observing networks. It chronologically describes the birth and formation of the various atmospheric measurement networks around the globe, which has mainly been driven by the need for atmospheric monitoring that provides long-term climate change observations. The relevance of networks, measurement principles, and the different parameters observed are presented. Quality control, maintenance, and future developments in this field to facilitate various applications are also discussed.

Atmospheric balloon soundings have been made since the end of the 19th century. In recent decades, specific upper-air radiosonde measurements have become important for climate monitoring and atmosp...

In-situ profiles of all four net radiation components were obtained at Ny Ålesund/Svalbard (78.9° N, 11.9° E) in the time frame May 04–21, 2015. Measurements could be performed using adapted high quality instrumentation classified as secondary standard carried by a tethered balloon system. Balloon lifted measurements of albedo under clear sky conditions demonstrate the altitude dependence of this parameter over heterogeneous terrain. Depending on the surface composition within the sensor's footprint, the albedo over predominantly snow covered surfaces was found to decrease to 53.4 % and 35.8 % compared to 73.1 % and 78.8 % measured with near surface references, respectively. Albedo profiles show an all-sky maximum at 150 m above surface level, and an averaged vertical change rate of −2.1 %/100 m (clear sky) and −3.4 %/100 m (overcast) above. Profiling of arctic low-level clouds reveals distinct vertical gradients in all radiation fluxes but longwave upward. Observed radiative cooling at cloud top with heating rates of −53 to −84 K/d in subsequent observations tend to be lower than suggested by 1-D simulations.

Since the mid-twentieth century, radiosonde and satellite measurements show that the troposphere has warmed and the stratosphere has cooled. These changes are primarily due to increasing concentrations of well-mixed greenhouse gases and the depletion of stratospheric ozone. In response to continued greenhouse gas increases and stratospheric ozone depletion, climate models project continued tropospheric warming and stratospheric cooling over the coming decades. Global average satellite observations of lower stratospheric temperatures exhibit no significant trends since the turn of the century. In contrast, an analysis of vertically resolved radiosonde measurements from 60 stations shows an increase of lower stratospheric temperature since the turn of the century at altitudes between 15 and 30 km and over most continents. Trend estimates are somewhat sensitive to homogeneity assessment choices, but all investigated radiosonde data sets suggest a change from late twentieth century cooling to early 21st century warming in the lower stratosphere, which is consistent with a reversal from ozone depletion to recovery from the effects of ozone-depleting substances. In comparison, satellite observations at the radiosonde locations show only minor early 21st century warming, possibly due to the compensating effects of continued cooling above the radiosonde altitude range.

In situ upper-air measurements are often made with instruments attached to weather balloons launched at the surface and lifted into the stratosphere. Present-day balloon-borne sensors allow near-continuous measurements from the Earth’s surface to about 35 km (3–5 hPa), where the balloons burst and their instrument payloads descend with parachutes. It has been demonstrated that ascending weather balloons can perturb the air measured by very sensitive humidity and temperature sensors trailing behind them, particularly in the upper troposphere and lower stratosphere (UTLS). The use of controlled balloon descent for such measurements has therefore been investigated and is described here. We distinguish between the single balloon technique that uses a simple automatic valve system to release helium from the balloon at a preset ambient pressure, and the double balloon technique that uses a carrier balloon to lift the payload and a parachute balloon to control the descent of instruments after the carrier balloon is released at preset altitude. The automatic valve technique has been used for several decades for water vapor soundings with frost point hygrometers, whereas the double balloon technique has recently been re-established and deployed to measure radiation and temperature profiles through the atmosphere. Double balloon soundings also strongly reduce pendulum motion of the payload, stabilizing radiation instruments during ascent. We present the flight characteristics of these two ballooning techniques and compare the quality of temperature and humidity measurements made during ascent and descent.

Atmospheric temperature and humidity profiles are important for weather prediction, but climate change has increased the interest in upper-air observations asking for very high-quality reference measurements. This paper discusses an experimental approach to determine the radiation-induced error on radiosonde air temperature measurements. On the one hand, solar shortwave and thermal longwave radiation profiles were accurately measured during radiosonde ascents from the surface to 35-km altitude. On the other hand, air temperature was measured with several thermocouples on the same flight, simultaneously under sun-shaded and unshaded conditions. The radiation experiments reveal that thermal radiation errors on the very thin thermocouple of the Meteolabor SRS-C34 radiosonde are similar during night- and daytime. They produce a radiative cooling in the lower troposphere and the upper stratosphere, but a radiative heating in the upper troposphere and lower stratosphere. Air temperature experiments with several thermocouples, however, show that solar radiation produces a radiative heating of about +0.2°C near the surface, which linearly increases to about +1°C at 32 km (~10 hPa). The new solar radiation error profile was then applied to SRS-C34 measurements made during the Eighth WMO Intercomparison of High Quality Radiosonde Systems, held in Yangjiang, China, in July 2010. The effects of thermal and solar radiation errors are finally shown in contrast to the 10 other internationally used radiosonde systems, which were flown during this international campaign.

[1] This study summarizes 53 years of radiosonde measurements at the MeteoSwiss Aerological Station of Payerne, Switzerland. The temperature time series is the result of a careful reassessment of the original data, mainly based on the internal station documentation. Comparisons with HadAT2 and RAOBCORE/RICH adjusted data sets document the high quality of our technical reevaluation. In the lower troposphere, we compare radiosonde measurement trends to independently homogenized surface trends measured at lowland and Alpine stations up to 3580 m. We find an average difference among trends below 0.03 K/decade (7–8%), showing consistency between upper air and surface temperature measurements. Upper air data show the 0°C isotherm to rise by about 70 m/decade on average over the whole period, which is consistent with the 60 m/decade trend found using surface measurements. A similar change has also been measured for the tropopause height, which rose by 54 m/decade over the last five decades. Analysis of the phase and amplitude of the diurnal temperature cycle shows a strongly decreasing amplitude with height from about 3 K at the surface to 0.2 K at 700 hPa. The diurnal cycle peaks at about 15 UTC at the surface and shifts to later hours with height, reaching almost midnight at 400 hPa. In the stratosphere, diurnal temperature again peaks at around 15 UTC, but with low amplitude. Annual temperature cycle amplitude is in the order of 15 K and fairly constant with height. The peak temperature, however, shifts from July–August in the troposphere to June–July in the stratosphere. Temperature trends in the troposphere exhibit a clear warming trend since the 1980s, which decreases with height and changes to a cooling trend in the stratosphere, with no trend or minor warming since the end of the 1990s. The warming in the troposphere is found to be larger during summer months, whereas the cooling in the stratosphere is larger during winter months.

The Raman Lidar for Meteorological Observations (RALMO) was installed at the MeteoSwiss Regional Center of Payerne, Switzerland, in summer 2008. One of its aims is to provide continuous vertical profiles of tropospheric water vapor during day and night at a high temporal resolution. Twelve months (October 2009–September 2010) of lidar data are analyzed. During this period of time, the lidar produced 9086 profiles, representing 52.6% of the time (this figure reached 63.2% for the first 6 months of 2011). Under cloud-free conditions, half of the profiles reached more than 8610 m above ground level at night, and 4050 m during the day. In order to validate the capabilities of the instrument, the year of lidar data was compared to the collocated radiosondes. On average, lidar water vapor mixing ratio was found to be within 5 to 10% of radiosonde values up to 8 km at night, and within 3% up to 3 km during the day. Relative humidity results show an agreement within 2 and 5% for day and night, respectively. An integrated water vapor comparison also shows a good correlation with both radiosondes and GPS measurements: the lidar had a 4.2% dry bias compared to radiosondes and a 5.3% wet bias compared to GPS. These results validate the performance of the lidar and the humidity profiles with a 30 min time resolution.

Upper-air balloon soundings for weather predictions have been made since the beginning of the 20th century. New radiosonde instruments for in situ humidity-, radiation- and gas-profile measurements in the troposphere and the lower stratosphere, were introduced in recent years for atmospheric research and climate monitoring, but such instruments are often expensive and it is desired they be reused on multiple flights. Recovering instruments that freely descend with parachutes is time consuming, sometimes difficult and even dangerous. Here, we introduce the return glider radiosonde (RGR), which enables flying and retrieving valuable in situ upper-air instruments. The RGR is lifted with weather balloons similar to traditional radiosondes to a preset altitude, at which time a release mechanism cuts the tether string, and a built-in autopilot flies the glider autonomously back to the launch site or a desired preprogrammed location. Once the RGR reaches the landing coordinates it circles down and releases a parachute 100m above ground for landing. The motivation for this project was to measure radiation profiles throughout the atmosphere with the same instrument multiple times and with a rapid turn-around time. The paper describes technical aspects of the return glider radiosonde and the built-in radiation instruments and shows test flights up to 24km altitude that are analyzed in terms of flight performance and maximal distances covered. Several successive flights measuring radiation profiles demonstrate the reliability and the operational readiness of the RGR, allowing new ways for atmospheric in situ research and monitoring with payloads up to several kg depending on the specific size of the glider., Atmospheric Measurement Techniques, 9 (6), ISSN:1867-1381, ISSN:1867-8548

At low elevations (500 m a.s.l.) Central Europe's surface temperature increased about 1.3 °C since 1981. Interestingly, at high elevations (2200 m a.s.l.) in the Alps, temperature rose less than 1 °C over the same period. Detailed investigations of temperature, humidity and the radiation budget at lowland and alpine climate stations now show that the difference in temperature rise is likely related to unequal solar- and greenhouse warming. The analysis shows that the important decline of anthropogenic aerosols in Europe since the mid-1980s led to solar brightening at low elevations, whereas inherent low aerosol concentrations at high elevations led to only minor changes of solar radiation in the Alps. In the Lowland, absolute humidity and also total net radiation show an about 6% K−1 Clausius–Clapeyron conform increase with temperature since the 1980s. In the Alps, however, the percentage increase rate of humidity and total net radiation is more than twice as large. This large water vapour increase in the Alps is likely related to strong warming and thermal advection in the Lowlands, and may also have increased due to atmospheric circulation changes. Hence, while in the Alps temperature increased primarily due to strong water vapour enhanced greenhouse warming, solar brightening combined with anthropogenic greenhouse gas and water vapour feedback greenhouse warming led to a higher temperature increase at low elevations in Central Europe. Copyright © 2012 Royal Meteorological Society

Verification results from different satellite-based surface shortwave irradiance retrievals and sensitivity runs for key input parameters are presented for the Alpine region. Overall the uncertainty of the hourly retrievals at the Federal Office of Meteorology and Climatology (MeteoSwiss) validated with high-quality surface measurements is comparable with results from the standard Heliosat-3 model, but clearly improved for situations with snow-cover. The sensitivity study reveals that it is recommended to precisely georeference the High Resolution Visible (HRV) and the Spinning Enhanced Visible and Infrared Imager (SEVIRI) channels of the Meteosat Second Generation (MSG) satellites to obtain accurate surface shortwave irradiance estimates. They also confirm the benefit of terrain corrections for sites located in deep Alpine valleys. Monthly mean shortwave irradiance retrievals provided by the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Satellite Application Facility on Climate Monitoring (CM-SAF) are verified with the MeteoSwiss products. For the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR)-based product about 60% of all satellite 15 km × 15 km grid cells match the MeteoSwiss product, if locally dependent 90% confidence intervals are applied. This percentage decreases to 52%, if the standard CM-SAF 90% confidence interval of 20 Wm-2 is used. Taking the local spatial variability of the shortwave irradiance field into account therefore allows obtaining more realistic verification results over heterogeneous terrain such as the Alpine region.

Net radiation flux in correlation with surface energy budget, snowmelt, glacier ice balance, and forest or agricultural flux exchange investigations is measured in numerous field experiments. Instrument costs and energy consumption versus performance and uncertainty of net radiation instruments has been widely discussed. Here the authors analyze and show performance and uncertainty of two Kipp and Zonen CNR1 net radiometers, which were compared to high standard reference radiation instruments measuring individual shortwave and longwave downward and upward flux components. The intercomparison was aimed at investigating the performance of the radiometers under different climatological conditions and was made over one year at the midlatitude Baseline Surface Radiation Network (BSRN) station in Payerne, Switzerland (490 MSL). Of the two CNR1 radiometers tested, one was installed in a ventilation and heating system, whereas the other was mounted without ventilation and heating. Uncertainties of the different flux components were found to be larger for shortwave than longwave radiation and larger for downward than upward components. Using the single sensitivity coefficient provided by the manufacturer, which for CNR1 radiometers conditions using all four sensors, rather large root-mean-square differences between 2 and 14 W m−2 were measured for the individual components for hourly averages and between 2 and 12 W m−2 for daily averages. The authors then performed a field calibration, comparing each individual sensor to the reference instrument for one particular day. With the individual field calibration the uncertainty of hourly averages was reduced significantly for all components of the ventilated and heated instrument. For the unventilated CNR1 uncertainties could not be reduced significantly for all sensors. The total net radiation uncertainty of both CNR1 is rather large with up to 26% on daily averages (∼10 W m−2) for the original sensitivity coefficients and without field calibration. Only with the field calibration and for the ventilated and heated CNR1 net radiometer is an uncertainty of 10% of the daily totals of total net radiation reached, as claimed by the manufacturer.

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 supporting tower structure. The observations cover all seasons and reveal the magnitude of longwave radiative flux divergence and its incoming and outgoing component under stable and unstable conditions. Longwave radiative flux divergence during winter corresponds to a radiative cooling of −10 K day−1, but values of −30 K day−1 can persist for several days. During summer, the mean cooling effect of longwave radiative flux divergence is small (−2 K day−1) but exhibits a strong diurnal cycle. With values ranging from −35 K day−1 around midnight to 15 K day−1 at noon, the heating rate due to longwave radiative flux divergence is of the same order of magnitude as the observed temperature tendency. However, temperature tendency and longwave radiative flux divergence are out of phase, with temperature tendency leading the longwave radiative flux divergence by 3 h. The vertical variation of the outgoing longwave flux usually dominates the net longwave flux divergence, showing a strong divergence at nighttime and a strong convergence during the day. The divergence of the incoming longwave flux plays a secondary role, showing a slight counteracting effect. Fog is frequently observed during summer nights. Under such conditions, a divergence of both incoming and outgoing fluxes leads to the strongest radiative cooling rates that are observed. Considering all data, a correlation between longwave radiative flux divergence and the temperature difference across the 2–48-m layer is found.

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 model alpine model (aLMo). MODTRAN computed LDR in Payerne using sounding data and ASRB observed LDR show an average difference of 1.5 W m -2 (±3.5 W m -2 ), and -3.2 W m -2 ±3.6 W m -2 ) for night- and daytime respectively from 1996 to 2001. Nighttime LDR is underestimated by the aLMo RTM in the order of -20 W m-2 compared to ASRB measurements both at Payerne and at six further ASRB sites. However LDR bias is strongly reduced in Payerne during daytime. For comparison MODTRAN computed LDR using aLMo forecasted atmospheric profiles shows mean differences in the order of -3 W m -2 both for night- and daytime. Hence the comprehensive radiation scheme used in aLMo is mainly responsible for the substantial underestimation of cloud-free LDR.

The greenhouse effect has been investigated predominantly with satellite measurements, but more than 90% of the greenhouse radiative flux affecting Earth’s surface temperature and humidity originates from a 1000 meter layer above the surface. Here we show that substantial improvements on surface longwave radiation measurements and very good agreement with radiative transfer model calculations allow the clear-sky greenhouse effect be determined with measured surface longwave radiation and calculated longwave outgoing radiation at the top of the atmosphere. The cloud radiative forcing is determined by measured net longwave fluxes and added to the clear-sky greenhouse effect to determine the all-sky greenhouse effect. Longwave radiation measurements at different altitudes were used to determine the clear-sky and all-sky annual and seasonal greenhouse effect and altitude gradients over the Alps. Linear altitude gradients are measured for clear-sky situations, whereas the all-sky greenhouse effect is strongly influenced by varying, cloud amounts at different altitudes. Large diurnal and seasonal variations show the importance of surface heating and cooling effects and demonstrate the strong coupling of the greenhouse effect to surface temperature and humidity.

¶The Alpine Surface Radiation Budget (ASRB) project was initiated in 1994 to investigate the altitude dependence of the surface radiation budget with a particular focus on accurate measurements of the longwave downward radiation. Meanwhile broadband short- and longwave radiation fluxes are continuously measured within this network at eleven stations between 370 and 3580 m a.s.l. in the Swiss Alps. New calibration techniques, modified pyrgeometers and an adequate ventilation and heating system decreased the uncertainty for longwave radiation measurements even under harsh alpine weather conditions to about ±3 W m−2.

Observations of high supersaturations with respect to ice inside cirrus clouds with high ice water content (> 0.01 g kg−1) and high crystal number densities (> 1 cm−3) are challenging our understanding of cloud microphysics and of climate feedback processes in the upper troposphere. However, single measurements of a cloudy air mass provide only a snapshot from which the persistence of ice supersaturation cannot be judged. We introduce here the "cirrus match technique" to obtain information about the evolution of clouds and their saturation ratio. The aim of these coordinated balloon soundings is to analyze the same air mass twice. To this end the standard radiosonde equipment is complemented by a frost point hygrometer, "SnowWhite", and a particle backscatter detector, "COBALD" (Compact Optical Backscatter AerosoL Detector). Extensive trajectory calculations based on regional weather model COSMO (Consortium for Small-Scale Modeling) forecasts are performed for flight planning, and COSMO analyses are used as a basis for comprehensive microphysical box modeling (with grid scale of 2 and 7 km, respectively). Here we present the results of matching a cirrus cloud to within 2–15 km, realized on 8 June 2010 over Payerne, Switzerland, and a location 120 km downstream close to Zurich. A thick cirrus cloud was detected over both measurement sites. We show that in order to quantitatively reproduce the measured particle backscatter ratios, the small-scale temperature fluctuations not resolved by COSMO must be superimposed on the trajectories. The stochastic nature of the fluctuations is captured by ensemble calculations. Possibilities for further improvements in the agreement with the measured backscatter data are investigated by assuming a very slow mass accommodation of water on ice, the presence of heterogeneous ice nuclei, or a wide span of (spheroidal) particle shapes. However, the resulting improvements from these microphysical refinements are moderate and comparable in magnitude with changes caused by assuming different regimes of temperature fluctuations for clear-sky or cloudy-sky conditions, highlighting the importance of proper treatment of subscale fluctuations. The model yields good agreement with the measured backscatter over both sites and reproduces the measured saturation ratios with respect to ice over Payerne. Conversely, the 30% in-cloud supersaturation measured in a massive 4 km thick cloud layer over Zurich cannot be reproduced, irrespective of the choice of meteorological or microphysical model parameters. The measured supersaturation can only be explained by either resorting to an unknown physical process, which prevents the ice particles from consuming the excess humidity, or – much more likely – by a measurement error, such as a contamination of the sensor housing of the SnowWhite hygrometer by a precipitation drop from a mixed-phase cloud just below the cirrus layer or from some very slight rain in the boundary layer. This uncertainty calls for in-flight checks or calibrations of hygrometers under the special humidity conditions in the upper troposphere., Atmospheric Chemistry and Physics, 14 (14), ISSN:1680-7375, ISSN:1680-7367

Because atmospheric longwave radiation is one of the most fundamental elements of an expected climate change, there has been a strong interest in improving measurements and model calculations in recent years. Important questions are how reliable and consistent are atmospheric longwave radiation measurements and calculations and what are the uncertainties? The First International Pyrgeometer and Absolute Sky-scanning Radiometer Comparison, which was held at the Atmospheric Radiation Measurement program's Southern Great Plains site in Oklahoma, answers these questions at least for midlatitude summer conditions and reflects the state of the art for atmospheric longwave radiation measurements and calculations. The 15 participating pyrgeometers were all calibration-traced standard instruments chosen from a broad international community. Two new chopped pyrgeometers also took part in the comparison. An absolute sky-scanning radiometer (ASR), which includes a pyroelectric detector and a reference blackbody source, was used for the first time as a reference standard instrument to field calibrate pyrgeometers during clear-sky nighttime measurements. Owner-provided and uniformly determined blackbody calibration factors were compared. Remarkable improvements and higher pyrgeometer precision were achieved with field calibration factors. Results of nighttime and daytime pyrgeometer precision and absolute uncertainty are presented for eight consecutive days of measurements, during which period downward longwave irradiance varied between 260 and 420 W m−2. Comparisons between pyrgeometers and the absolute ASR, the atmospheric emitted radiance interferometer, and radiative transfer models LBLRTM and MODTRAN show a surprisingly good agreement of

We compare three different methods for determining an average ‘effective‧ UV albedo. These methods are applied to spectral irradiance data from a measurement campaign held in the German Alps during the spring of 1999. The first method is based on the comparison of measurements of absolute levels of UV irradiance with model calculations. The second method takes advantage of changes in the spectral slope of spectral UV irradiance, which is a function of the surface albedo. In the third method, the surrounding area is partitioned into snow-covered and snow-free regions, and the effective albedo estimated by applying a higher or lower reflectivity to each facet before integrating over the surroundings. We present the differences and the correlations between the various methods as well as the results for the different locations.

The Alps are one of the regions in Europe showing very high erythemal UV irradiance (UVery) which is a consequence of low aerosol levels, high altitude and snow-covered surfaces. Effective albedo plays a key role in understanding the radiative transfer over an Alpine terrain. The difficulty in determining the effective albedo is predominantly due to inhomogeneous surfaces in Alpine regions and a number of interrelated parameters. Most of these parameters can be corrected or normalized by simple methods. The effect of total ozone on different components of the erythemal UV irradiance and the influence of aerosols have been largely investigated and are determined by model calculations. After these atmospheric corrections or normalizations the albedo of the surrounding surfaces within a radius of about 25 km is the only remaining influence to be taken into account on the ratio between direct and diffuse UVery radiation. Satellite data from selected days allowed us to determine the fraction of snow coverage within this radius and to weight the effect of the surrounding surfaces on UVery radiation. With this information from space and data from local albedo measurements in the erythemal UV, it is possible to calculate effective albedo values for these selected days. A correlation between effective albedo and the ratio direct to diffuse was found to be linear for constant solar elevations. Hence this correlation allows us to determine effective albedo at any Alpine location with accurate measurements of direct and diffuse UVery radiation. It is shown from this investigation that the albedo effect can enhance diffuse UVery radiation by up to 57% and global UVery radiation by 30%, especially in spring.

Seven spectroradiorneters measured simultaneous surface UV irradiances at six different sites in the vicinity of Garmisch-Partenkirchen, Germany, during spring 1999. The measured clear-sky irradiance variability between the sites was analyzed with respect to altitude, aerosol optical depth, solar zenith angle, effective albedo, and tropospheric ozone. For conditions of low aerosol loading the increase of irradiance per 1000 m altitude difference was 9% at 400 nm. 20% at 320 nm, and 30% at 300 nm in this season. Effective albedo differences of 0.15, 0.29, and 0.65 were found between the snow-covered stations and the snow-free ground station with the higher effective albedo values determined at the two mountain stations. Clean continental aerosols with a single-scatter albedo of 0.95 were observed during this campaign. The measurements and the observed variations between the sites should enable more accurate modeling studies to be performed for an Alpine environment.

Accuratesurfaceradiationfluxesarerequiredto quantify atmosphere-surface energy exchanges. In climate research, detailed investigations of the influence of diverse atmospheric conditions on radiative fluxes ask for a well- dened distinction between clear-sky and cloudy-sky situa- tions. Eects of clouds, the so called \cloud forcing", can only be determined by explicitly separating clear-sky from all-sky radiation measurements. A Clear-Sky Index (CSI) to separate clear-sky from cloudy-sky situations has there- fore been introduced, using accurate atmospheric longwave radiation in conjunction with air temperature and humid- itymeasurementsatthestation. Thisclear-skyindex,which hastheimportantadvantagetobeapplicable24hoursaday, wastestedandrstusedonmeasurementsoftheAlpineSur- face Radiation Budget (ASRB) network, and was of prime importanceforthedeterminationofthealtitudedependence of cloud forcing and greenhouse eect over the Alps.

Global, direct and diffuse measurements of erythemal UV radiation with UV-Biometer and radiative transfer calculations are used to estimate the influences of (1) a snow-covered surface, (2) an overcast sky, and (3) a joined snow-covered surface and overcast sky at Davos (1610 m asl, Swiss Alps). The influence of total ozone, zenith angle, and aerosol are first investigated. The influence of surface albedo and clouds are then estimated as a function of the zenith angle after normalization of the data to a fixed ozone amount. If the ground is covered with snow on clear-sky days at Davos, erythemal irradiance increases by 15 to 25% due to multiple reflections between the surface and the atmosphere. This relative increase may reach 80% on overcast days. The highly significant dependence of the albedo on solar elevation is most probably due to inhomogeneities in the surrounding terrain leading to a strong non-Lambertian behavior. The impact of clouds on radiation is highly variable: on overcast days with a snow free surface, erythemal UV radiation at Davos is reduced to a level ranging between 8% (very thick cloud cover) and 70% (thin cloud layer) relative to the radiation under clear-sky conditions.

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.

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.

[1] Solar shortwave and thermal longwave radiation at the Earth's surface and at the top of the atmosphere is commonly measured at surface stations, from airplanes and from satellites. Here we show radiative flux profiles measured with radiosondes ascending from the Earth's surface to 35 km into the stratosphere. During two-hour flights solar shortwave and thermal longwave radiation are measured both downward and upward with four individual sensors. Daytime solar and thermal radiation is compared to nighttime measurements and 24-hour average radiation budget profiles are shown through the atmosphere. However, of even greater importance with regard to climate change are measured upward and downward longwave greenhouse radiation profiles. Their changes with temperature and water vapor enable direct measurement of radiative forcing through the atmosphere. Measurements during two cloud-free nights with different temperature and different water vapor amount, show an almost equal but opposite net longwave radiation change, or water vapor greenhouse forcing, downwards to the surface and upward into space. Radiative flux profiles clearly illustrate the Earth's atmospheric greenhouse effect, and allow important investigations of clouds and other atmospheric constituents and their effects on shortwave reflection, as well as longwave emission towards the surface and into space.

A laboratory test facility for solar radiation detectors has been built and is in operation at the Aerological Station of the Swiss Meteorological Institute (SAP/SMI). This installation is conceived as a universal test bed for solar radiation exposed meteorological instruments, and consists of a commercially available solar simulator, a laser alignment system, a translation mechanism with instrument mounts, and an adjustable projection mirror. The solar simulator produces a well characterized radiation beam which can be filtered to match the terrestrial or outer space solar spectrum with an irradiance of up to one solar constant (1367 Wm −2 ). The instrument mounts and a HeNe laser beam provide a precise and easy alignment of the reference and the test instruments in the radiation beam, allowing for incident angles in the range of 15°–75°. The measurement is based on a comparison of the response of an active cavity absolute radiometer PMO6 with the signal of the test instrument. Detailed investigations of the Haenni Solar 111B type heliometer have revealed important irregularities in the sunshine threshold irradiance angular distribution. Measurements performed with and without the protection glass cover prove the exceedingly high threshold values at large declination angles to be a consequence of enhanced reflections due to the incident angle and inhomogeneities in the glass cover. Very satisfactory results have also been obtained on characterization measurements of pyranometers showing the mean values of the responsivity to be within 0.8% of the calibration values measured at the world radiation center (WRC) at Davos.

Recent far infrared collective scattering measurements on the DIII-D tokamak during H mode operation have provided a more complete understanding of the L to H transition, and have confirmed the interpretation of previous reflectometry data. The frequency spectra of fluctuations measured during the neutral beam heated L and H mode discharges in DIII-D are dominated by E × B Doppler shifts. This fact is utilized to enhance the spatial localization of scattering data through knowledge of the measured variation in the radial electric field, Er. Scattering data interpreted in this way indicate a rapid (≈100 μs) reduction in the edge density fluctuation level coincident with the L to H transition, thereby quantifying and confirming the interpretation of previously obtained reflectometer data. The reduction in the RMS electron density fluctuation level (ne) is ≥50%. Additionally, the presence of increased electric field shear is observed in the region where the fluctuations are strongly suppressed, as determined from the reduction and broadening of the scattered auto-power spectrum associated with the plasma edge inside the separatrix. Finally, the poloidal wavenumber spectrum has been characterized across the L to H mode transition, indicating that there are no significant modifications to the spectral width over the H mode parameter range investigated

A series of H-mode discharges from DIII-D has been analysed to find a possible correlation between turbulent fluctuations and thermal transport in the core of the DIII-D tokamak. The one-fluid thermal diffusivity as given by the transport code ONETWO is observed to peak in the region 0.7 ≤ ρ ≤ 0.9 where the bulk of the electrostatic fluctuations is located in the H-mode. Also the time evolution of the thermal diffusivity and the fluctuations in this region are very similar: both transport and fluctuations are suppressed after the L-H transition, but the suppression is not abrupt (as it is at the edge) but rather gradual, extending over tens of milliseconds. It is thus concluded that transport and microturbulence in the interior of the DIII-D plasmas appear to be strongly correlated

At the onset of the L–H transition in the DIII‐D tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p.159], a fast (≊100 μsec) suppression of microturbulence is observed as the edge transport barrier is formed. This fast edge suppression is followed by a much slower (tens of msec), but substantial (≥50%) reduction in the relative density fluctuation level. This second turbulence suppression phase, which is observed to correlate with growing E×B velocity shear, has been localized to the plasma interior, and may explain why the observed transport reduction in the H mode has been observed to extend deep into the plasma, well beyond the edge transport barrier.

A comparison of three different infrared detectors in the 10.6-μm region is presented. A method for measuring the frequency response from dc up to 100 MHz in a continuous way is developed. We show that the flatness of the frequency response does not only depend on the electronic circuit following the detector, matching the impedance between the detector and the preamplifier, but also on the parallelism of the local oscillator and the signal beam. The signal-to-noise ratio of the detector signal is improved and reaches the theoretical limit by chopping only the signal beam and detecting the spectral analyzed intermediate frequency signal with the lock-in technique. Detecting the signal in this new way suppresses externally detected noise, which is omnipresent in weak signal detection.

[1] Aerosol indirect effects are some of the largest uncertainties of anthropogenic climate change. To estimate the first aerosol indirect radiative effect (or cloud albedo effect), we analyzed global solar irradiance measurements under completely overcast skies during the recent period of aerosol optical depth decline in Europe. Although measurements from 15 Swiss and 8 northern German sites show clear evidence for an aerosol direct radiative effect under cloud-free skies, trends of transmitted solar irradiance (SWtran) under overcast skies are ambiguous. Time series from 1981 to 2005 of SWtran for all overcast conditions show slightly negative, but nonsignificant trends. SWtran under overcast conditions with “thick” clouds (SWtran smaller than the long-term mean) exhibit on average an increasing trend of +0.29 [+0.01 to +0.57] W m−2/decade. The increase of SWtran under “thick” overcast skies, however, is about nine times smaller than the increase under cloud-free skies. Since cirrus clouds are generally excluded from and low-level stratiform clouds are more frequently represented by “thick” overcast skies, the slight increase in SWtran may possibly result from a weak aerosol indirect effect. Alternatively, the increase in SWtran may be due to a decreasing trend in low-level stratiform cloud amount under overcast conditions observed for these sites. We further find that solar irradiance changes caused by decreasing aerosol direct effect and increasing sunshine duration can account for most of the observed increasing all-sky solar radiation trend. This suggests that the first aerosol indirect effect makes little contribution to surface solar radiation changes over Europe.

A decrease in the edge magnetic and density fluctuations is always seen at the L-H transition in DIII-D. Also, a sudden change of the perpendicular rotation vperpendicular to in the edge has been observed at the transition, which indicates the formation of shear in the radial electric field. This region coincides with the region where the density fluctuations are suppressed. These experimental observations are consistent with earlier theoretical models. Comparisons between the theories and the experimental observations will be discussed.

[1] Mainland Europe's temperature rise of about 1°C since the 1980s is considerably larger than expected from anthropogenic greenhouse warming. Here we analyse shortwave and longwave surface forcings measured in Switzerland and Northern Germany and relate them to humidity- and temperature increases through the radiation- and energy budget. Shortwave climate forcing from direct aerosol effects is found to be much larger than indirect aerosol cloud forcing, and the total shortwave forcing, that is related to the observed 60% aerosol decline, is two to three times larger than the longwave forcing from rising anthropogenic greenhouse gases. Almost tree quarters of all the shortwave and longwave forcing energy goes into the turbulent fluxes, which increases atmospheric humidity and hence the longwave forcing by water vapour feedback. With anthropogenic aerosols now reaching low and stable values in Europe, solar forcing will subside and future temperature will mainly rise due to anthropogenic greenhouse gas warming.

The L to H transition in the DIII‐D tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1986 (IAEA, Vienna, 1987), Vol. I, p. 159] is associated with two clear signatures: edge density fluctuations are abruptly suppressed (in ≊100 μsec), while the edge poloidal rotation velocity vθ increases, implying that the radial electric field Er becomes more negative. Detailed new spectroscopic profile measurements show that the changes in vθ and Er generate a region of sheared electric field and poloidal flow of width ≊3–5 cm. This region develops simultaneously with, and has the same spatial extent as, the edge fluctuation suppression zone as measured using a reflectometer system. Furthermore, the radial extent of the shear and fluctuation suppression zones encompass the location of the H‐mode edge transport barrier. These observations are consistent with recent theoretical models of the L–H transition, and a comparison with these theories is presented. Data are also presented on the evolution of edge parameters and density fluctuations after the transition: the shear and fluctuation suppression layers are maintained for the duration of the quiescent H‐mode phase, while relative density fluctuation levels decrease and interior plasma confinement gradually improves. Precursors to several different types of edge localized mode (ELMs) are also discussed.

[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 and Switzerland. The measurements show a decline in aerosol concentration of up to 60%, which have led to a statistically significant increase of solar irradiance under cloud-free skies since the 1980s. The measurements confirm solar brightening and show that the direct aerosol effect had an approximately five times larger impact on climate forcing than the indirect aerosol and other cloud effects. The overall aerosol and cloud induced surface climate forcing is ∼+1 W m−2 dec−1 and has most probably strongly contributed to the recent rapid warming in Europe.

Atmospheric long-wave radiation is one of the most promising parameters for observations of climate change that are greenhouse effect related. Long-wave irradiance is usually measured with pyrgeometers that consist of a flat thermopile and a hemispherical dome acting as a filter and protecting the absorbing receiver surface. Pyrgeometers are blackbody calibrated, but uncertainties, mainly related to the silicon hemisphere, arise from thermal effects, inadequate spectral transmission, and cosine-response errors. The new absolute sky-scanning radiometer (ASR) allows absolute measurements of atmospheric long-wave radiation and is suggested as a future reference standard for pyrgeometer field calibration. The calibration of the ASR is based on a reference blackbody source traced to absolute temperature standards. The pyroelectric detector has no window to prevent thermal and spectral transmission effects. Scanning the sky with a narrow viewing angle and integrating with the Gaussian quadrature, rather than taking hemispherical measurements, prevent errors related to the cosine effect.

Anomalous transport in fusion plasmas remains an enigma requiring explanation. A predictive capability is highly desirable if confinement enhancement regimes such as H mode or super shots are to be extrapolated to the next phase in development of the International Fusion program, epitomized, for example in ITER. Therefore, identification of the role that electrostatic turbulence plays in confinement is a critical issue requiring detailed experimental data capable of testing and challenging existing theoretical models. This article presents microturbulence measurements obtained on the DIII‐D and TEXT tokamaks utilizing heterodyne, far‐infrared collective scattering, and reflectometry techniques. The experimental systems are described on both machines and emphasis placed on results obtained during the L‐H transition, ELM activity, and saturated ohmic operation where ion temperature gradient driven (ITGD) turbulence is theoretically predicted to exist.

The L to H transition in the DIII‐D tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1986 (IAEA, Vienna, 1987), Vol. I, p. 159] is associated with a decrease in the edge density and magnetic fluctuations. In addition, in single‐null divertor plasmas, a reduction in the heat flux asymmetry between the inner and outer divertor hit spots occurs. These observations indicate that the L to H transition is associated with the reduction in anomalous, fluctuation‐connected transport across the outer midplane of the plasma. Magnetic fluctuations are measured with a poloidally distributed set of Mirnov loops while density fluctuations are detected with multiple fixed‐frequency microwave reflectometers. Spectroscopic observations of edge poloidal and toroidal rotation have allowed the inference that the radial electric field just inside the separatrix is negative in the L mode and becomes more negative at the L to H transition. These changes in fluctuations and in the edge electric field occur in plasma...

[1] Atmospheric radiative transfer model estimates of diffuse horizontal broadband shortwave (solar) irradiance have historically been larger than measurements from a shaded pyranometer. A reference standard for the diffuse horizontal shortwave irradiance does not exist. There are no current efforts to develop an absolute standard that are known to the authors. This paper presents the case for a working standard for this measurement. Four well-behaved pyranometers from two previous intensive observation periods (IOP) were chosen for this study. The instruments were characterized for spectral and angular response before the IOP and calibrated during the IOP using a shade/unshade technique with reference direct irradiance from an absolute cavity radiometer. The results of the comparison and detailed analyses to explain the differences suggest selecting three of the four for the working standard. The 95% confidence uncertainty in this standard is estimated at 2.2% of reading + 0.2 W/m2. In lieu of a comparison to this trio, a procedure for obtaining low-uncertainty diffuse horizontal shortwave irradiance is suggested.