ALBERT

Description: A ground-based field campaign was conducted in southern West Africa from mid-June to the end of July 2016 within the framework of the Dynamics–Aerosol–Chemistry–Cloud Interactions in West Africa (DACCIWA) project. It aimed to provide a high-quality comprehensive data set for process studies, in particular of interactions between low-level clouds (LLCs) and boundary-layer conditions. In this region missing observations are still a major issue. During the campaign, extensive remote sensing and in situ measurements were conducted at three supersites: Kumasi (Ghana), Savè (Benin) and Ile-Ife (Nigeria). Daily radiosoundings were performed at 06:00 UTC, and 15 intensive observation periods (IOPs) were performed during which additional radiosondes were launched, and remotely piloted aerial systems were operated. Extended stratiform LLCs form frequently in southern West Africa during the nighttime and persist long into the following day. They affect the radiation budget and hence the evolution of the atmospheric boundary layer and regional climate. The relevant parameters and processes governing the formation and dissolution of the LLCs are still not fully understood. This paper gives an overview of the diurnal cycles of the energy-balance components, near-surface temperature, humidity, wind speed and direction as well as of the conditions (LLCs, low-level jet) in the boundary layer at the supersites and relates them to synoptic-scale conditions (monsoon layer, harmattan layer, African easterly jet, tropospheric stratification) in the DACCIWA operational area. The characteristics of LLCs vary considerably from day to day, including a few almost cloud-free nights. During cloudy nights we found large differences in the LLCs' formation and dissolution times as well as in the cloud-base height. The differences exist at individual sites and also between the sites. The synoptic conditions are characterized by a monsoon layer with south-westerly winds, on average about 1.9 km deep, and easterly winds above; the depth and strength of the monsoon flow show great day-to-day variability. Within the monsoon layer, a nocturnal low-level jet forms in approximately the same layer as the LLC. Its strength and duration is highly variable from night to night. This unique data set will allow us to test some new hypotheses about the processes involved in the development of LLCs and their interaction with the boundary layer and can also be used for model evaluation.

Description: Post-depositional fractionation of stable water isotopes due to fractionating surface evaporation introduces uncertainty to various isotope applications such as the reconstruction of paleotemperatures, paleoaltimetry, and the investigation of groundwater formation. In this study, we investigate isotope fractionation at snow-covered moisture sources by combining 17 months of observations of isotope concentration ratios [HD16O] ∕ [H216O] in low-level water vapor in central Europe with a new Lagrangian isotope model. The isotope model is capable of reproducing variations of the observed isotope ratios with a correlation coefficient R of 0.82. Observations from 38 days were associated with cold snaps and moisture uptake in snow-covered regions. Deviations between modeled and measured isotope ratios during the cold snaps were related to differences in skin temperatures (Tskin). Analysis of Tskin provided by the Global Data Assimilation System (GDAS) of the NCEP implies the existence of two regimes of Tskin with different types of isotope fractionation during evaporation: a cold regime with Tskin 

Description: The HD(CP)2 Observational Prototype Experiment (HOPE) was performed as a major 2-month field experiment in Jülich, Germany, in April and May 2013, followed by a smaller campaign in Melpitz, Germany, in September 2013. HOPE has been designed to provide an observational dataset for a critical evaluation of the new German community atmospheric icosahedral non-hydrostatic (ICON) model at the scale of the model simulations and further to provide information on land-surface–atmospheric boundary layer exchange, cloud and precipitation processes, as well as sub-grid variability and microphysical properties that are subject to parameterizations. HOPE focuses on the onset of clouds and precipitation in the convective atmospheric boundary layer. This paper summarizes the instrument set-ups, the intensive observation periods, and example results from both campaigns. HOPE-Jülich instrumentation included a radio sounding station, 4 Doppler lidars, 4 Raman lidars (3 of them provide temperature, 3 of them water vapour, and all of them particle backscatter data), 1 water vapour differential absorption lidar, 3 cloud radars, 5 microwave radiometers, 3 rain radars, 6 sky imagers, 99 pyranometers, and 5 sun photometers operated at different sites, some of them in synergy. The HOPE-Melpitz campaign combined ground-based remote sensing of aerosols and clouds with helicopter- and balloon-based in situ observations in the atmospheric column and at the surface. HOPE provided an unprecedented collection of atmospheric dynamical, thermodynamical, and micro- and macrophysical properties of aerosols, clouds, and precipitation with high spatial and temporal resolution within a cube of approximately 10  ×  10  ×  10 km3. HOPE data will significantly contribute to our understanding of boundary layer dynamics and the formation of clouds and precipitation. The datasets have been made available through a dedicated data portal. First applications of HOPE data for model evaluation have shown a general agreement between observed and modelled boundary layer height, turbulence characteristics, and cloud coverage, but they also point to significant differences that deserve further investigations from both the observational and the modelling perspective.

Description: Repeated, grid-based forest soil inventories such as the nationwide German forest soil survey (GFSI) aim, among other things, at detecting changes in soil properties and plant nutrition. In these types of inventories, the only information on soil phosphorus (P) is commonly the total P content. However, total P content in mineral soils of forests is usually not a meaningful variable to predict the availability of P to trees. Here we tested a modified sequential P extraction ac-cording to Hedley to determine the distribution of different plant available P fractions in soil samples (0–5 and 10–30 cm depth) from 146 GFSI sites, capturing a wide variety of soil conditions. In addition, we analyzed relationships between these P fractions and common soil proper-ties such as pH, texture, and organic Carbon content (SOC). Total P content among our samples ranged from approximately 60 up to 2800 mg kg−1. The labile, moderately labile, and stable P fractions contributed to 27 %, 51 % and 22 % of total P content, respectively, at 0–5 cm depth. At 10–30 cm depth, the labile P fractions decreased to 15 %, whereas the stable P fractions in-creased to 30 %. These changes with depth were accompanied by a decrease in the organic P fractions. High P contents were related with high pH-values. Whereas the labile P pool increased with decreasing pH in absolute and relative terms, the stable P pool decreased in absolute and relative terms. Increasing SOC in soils led to significant increases in all P pools and in total P. In sandy soils, the P content across all fractions was lower than in other soil texture types. Multiple linear regressions indicated that P pools and P fractions were moderately well related to soil properties (r2 mostly above 0.5), and sand content of soils had the strongest influence. Foliage P concentrations in Pinus sylvestris were reasonably well explained by the labile and moderately labile P pool (r

Description: The "HD(CP)2 Observational Prototype Experiment" (HOPE) was executed as a major 2-month field experiment in Jülich, Germany, performed in April and May 2013, followed by a smaller campaign in Melpitz, Germany in September 2013. HOPE has been designed to provide a critical evaluation of the new German community atmospheric Icosahedral non-hydrostatic (ICON) model at the scale of the model simulations and further to provide information on land-surface-atmospheric boundary layer exchange, cloud and precipitation processes as well as on sub-grid variability and microphysical properties that are subject to parameterizations. HOPE focuses on the onset of clouds and precipitation in the convective atmospheric boundary layer. The paper summarizes the instrument set-ups, the intensive observation periods as well as example results from both campaigns. HOPE-Jülich instrumentation included a radio sounding station, 4 Doppler lidars, 4 Raman lidars (3, 3, and 4 of these provide temperature, water vapor, and particle backscatter data, respectively), 1 water vapour differential absorption lidar, 3 cloud radars, 5 microwave radiometers, 3 rain radars, 6 sky imagers, 99 pyranometers, and 5 Sun photometers operated in synergy at different supersites. The HOPE-Melpitz campaign combined ground-based remote sensing of aerosols and clouds with helicopter- and balloon-based in-situ observations in the atmospheric column and at the surface. HOPE provided an unprecedented collection of atmospheric dynamical, thermodynamical, and micro- and macrophysical properties of aerosols, clouds and precipitation with high spatial and temporal resolution within a cube of approximately 10 × 10 × 10 km3. HOPE data will significantly contribute to our understanding of boundary layer dynamics and the formation of clouds and precipitation. The datasets are made available through a dedicated data portal.

Description: Post-depositional fractionation of stable water isotopes due to fractioning surface evaporation introduces uncertainty to various isotope applications such as the reconstruction of paleotemperatures, paleoaltimetry, and the investigation of ground-water formation. In this study, we investigate isotope fractionation during the evaporation of snow at ground level by combining 17 months of observations of isotope concentration ratios [HD16O]/[H216O] in low-level water vapor in Central Europe with a new Lagrangian isotope model. The isotope model is capable of reproducing variations of the observed isotope ratios with a correlation coefficient R of 0.82. Deviations between modeled and measured isotope ratios during cold snaps were related to differences in skin temperatures (Tskin). Analysis of Tskin provided by the Global Data Assimilation System (GDAS) of the NCEP implies the existence of two regimes of Tskin with different types of isotope fractionation during evaporation: A cold regime with Tskin 〈 Tsubl,max = −7.1 °C, which is dominated by non-fractioning sublimation of snow and a warmer regime with Tsubl,max 〈 Tskin 〈 0 °C, which is dominated by fractioning evaporation of meltwater. Based on a sensitivity study, we assess an uncertainty range of the determined Tsubl,max of −11.5 to −2.5 °C.

Description: A ground-based field campaign was conducted in southern West Africa from mid June to the end of July 2016 within the framework of the Dynamics–Aerosol–Chemistry–Cloud Interactions in West Africa (DACCIWA) project. It aimed to provide a high-quality comprehensive data set for process studies, in particular into interactions between low-level clouds (LLCs) and boundary-layer conditions. In this region missing observations are still a major issue. During the campaign, extensive remote sensing and in-situ measurements were conducted at three supersites: Kumasi (Ghana), Savè (Benin) and Ile-Ife (Nigeria). Daily radiosoundings were performed at 06:00 UTC and 15 intensive observation periods (IOPs) were performed during which additional radiosondes were launched every 1.5 to 3 h. Remotely piloted aerial systems were also operated during the IOPs. Extended stratiform LLCs form frequently in southern West Africa during the night time and persist long into the following day. They affect the radiation budget and hence the evolution of the atmospheric boundary layer and regional climate. The relevant parameters and processes governing the formation and dissolution of the LLCs are still not fully understood. This paper gives an overview of the diurnal cycles of the energy-balance components, near-surface temperature, humidity, wind speed and direction as well as the conditions (LLCs, low-level jet) in the boundary layer at the supersites and relates them to synoptic-scale conditions (monsoon layer, Harmattan layer, African easterly jet, tropospheric stratification) in the DACCIWA operational area. The characteristics of LLCs vary considerably from day to day, including a few almost cloud-free nights. During cloudy nights we found large differences in the LLC's formation and dissolution times as well as in the cloud-base height. The differences exist at individual sites and also between the sites. The synoptic conditions are characterised by a monsoon layer with south-westerly wind, on average about 1.9 km deep, and easterly wind above; the depth and strength of the monsoon flow show great day-to-day variability. Within the monsoon layer, a nocturnal low-level jet forms in approximately the same layer as the LLC. Its strength and duration is highly variable from night to night. This unique data set will allow us to test some new hypotheses about the processes involved in the development of LLCs and their interaction with the boundary layer and can also be used for model evaluation.

Description: Repeated, grid-based forest soil inventories such as the National Forest Soil Inventory of Germany (NFSI) aim, among other things, at detecting changes in soil properties and plant nutrition. In these types of inventories, the only information on soil phosphorus (P) is commonly the total P content. However, total P content in mineral soils of forests is usually not a meaningful variable with respect to predicting the availability of P to trees. Here we tested a modified sequential P extraction according to Hedley (1982) to determine the distribution of different plant-available P fractions in soil samples (at depths of 0–5 and 10–30 cm) from 146 NFSI sites, encompassing a wide variety of soil conditions. In addition, we analyzed relationships between these P fractions and common soil properties such as pH, texture, and soil organic carbon content (SOC). The total P content among our samples ranged from approximately 60 to 2800 mg kg−1. The labile, moderately labile, and stable P fractions contributed to 27 %, 51 %, and 22 % of the total P content, respectively, at a depth of 0–5 cm. At a depth of 10–30 cm, the labile P fractions decreased to 15 %, whereas the stable P fractions increased to 30 %. These changes with depth were accompanied by a decrease in the organic P fractions. High P contents were related to high pH values. While the labile Hedley P pool increased with decreasing pH in absolute and relative terms, the stable Hedley P pool decreased in absolute and relative terms. Increasing SOC in soils led to significant increases in all Hedley P pools and in total P. In sandy soils, the P content across all fractions was lower than in other soil texture types. Multiple linear regression models indicated that Hedley P pools and P fractions were moderately well related to soil properties (with r2 values that were mostly above 0.5), and that the sand content of soils had the strongest influence. Foliar P contents in Pinus sylvestris were reasonably well explained by the labile and moderately labile P pool (r2 = 0.67) but not so for Picea abies and Fagus sylvatica. Foliar P contents in all three species could not be related to specific Hedley P pools. Our study indicates that soil properties such as pH, SOC content, and soil texture may be used to predict certain soil Hedley P pools with different plant availability on the basis of large soil inventories. However, the foliar P contents of tree species cannot be sufficiently well predicted by the soil variables considered here.