ERA-CLIM Historical Upper-Air Data 1900-1972

Historical, i.e. pre-1957, upper-air data are a valuable source of information on the state of the atmosphere, in some parts of the World back to the early 20th century. However, to date reanalyses have only partially made use of these data, and only of observations made after 1948. Even for the period between 1948 (the starting year of the NCEP/NCAR reanalysis) and the International Geophysical Year in 1957 (the starting year of the ERA-40 reanalysis), when the global upper-air coverage reached more or less its current status, many observations have not been digitised until now. The Comprehensive Historical Upper-Air Network (CHUAN) already compiled a large collection of pre-1957 upper-air data. In the framework of the European project ERA-CLIM, significant amounts of additional upper-air data have been catalogued (> 1.3 mio station days), imaged (> 200,000 images) and digitised (> 700,000 station days) in order to prepare a new input dataset for upcoming reanalyses. The records cover large parts of the globe, focussing on so far less well covered regions such as the Tropics, the polar regions and the Oceans, and on very early upper-air data from Europe and the US. The total number of digitised/inventoried records is 61/101 for moving upper-air data, i.e. data from ships etc., and 735/1,783 for fixed upper-air stations. Here, we give a detailed description of the resulting dataset including the metadata and the quality checking procedures applied. The data will be included in the next version of CHUAN.

(Table 1) Age determination of stalagmites of the Marcello Arévalo Cave in Chile

Stalagmites are important palaeo-climatic archives since their chemical and isotopic signatures have the potential to record high-resolution changes in temperature and precipitation over thousands of years. We present three U/Th-dated records of stalagmites (MA1-MA3) in the superhumid southern Andes, Chile (53°S). They grew simultaneously during the last five thousand years (ka BP) in a cave that developed in schist and granodiorite. Major and trace elements as well as the C and O isotope compositions of the stalagmites were analysed at high spatial and temporal resolution as proxies for palaeo-temperature and palaeo-precipitation. Calibrations are based on data from five years of monitoring the climate and hydrology inside and outside the cave and on data from 100 years of regional weather station records. Water-insoluble elements such as Y and HREE in the stalagmites indicate the amount of incorporated siliciclastic detritus. Monitoring shows that the quantity of detritus is controlled by the drip water rate once a threshold level has been exceeded. In general, drip rate variations of the stalagmites depend on the amount of rainfall. However, different drip-water pathways above each drip location gave rise to individual drip rate levels. Only one of the three stalagmites (MA1) had sufficiently high drip rates to record detrital proxies over its complete length. Carbonate-compatible element contents (e.g. U, Sr, Mg), which were measured up to sub-annual resolution, document changes in meteoric precipitation and related drip-water dilution. In addition, these soluble elements are controlled by leaching during weathering of the host rock and soils depending on the pH of acidic pore waters in the peaty soils of the cave's catchment area. In general, higher rainfall resulted in a lower concentration of these elements and vice versa. The Mg/Ca record of stalagmite MA1 was calibrated against meteoric precipitation records for the last 100 years from two regional weather stations. Carbonate-compatible soluble elements show similar patterns in the three stalagmites with generally high values when drip rates and detrital tracers were low and vice versa. d13C and d18O values are highly correlated in each stalagmite suggesting a predominantly drip rate dependent kinetic control by evaporation and/or outgassing. Only C and O isotopes from stalagmite MA1 that received the highest drip rates show a good correlation between detrital proxy elements and carbonate-compatible elements. A temperature-related change in rainwater isotope values modified the MA1 record during the Little Ice Age (~0.7-0.1 ka BP) that was ~1.5 °C colder than today. The isotopic composition of the stalagmites MA2 and MA3 that formed at lower drip rates shows a poor correlation with stalagmite MA1 and all other chemical proxies of MA1. 'Hendy tests' indicate that the degassing-controlled isotope fractionation of MA2 and MA3 had already started at the cave roof, especially when drip rates were low. Changing pathways and residence times of the seepage water caused a non-climatically controlled isotope fractionation, which may be generally important in ventilated caves during phases of low drip rates. Our proxies indicate that the Neoglacial cold phases from ~3.5 to 2.5 and from ~0.7 to 0.1 ka BP were characterised by 30% lower precipitation compared with the Medieval Warm Period from 1.2 to 0.8 ka BP, which was extremely humid in this region.

Optical depth of Atlantic dust as netCDF files

African dust outbreaks are the result of complex interactions between the land, atmosphere, and oceans, and only recently has a large body of work begun to emerge that aims to understand the controls on-and impacts of-African dust. At the same time, long-term records of dust outbreaks are either inferred from visibility data from weather stations or confined to a few in situ observational sites. Satellites provide the best opportunity for studying the large-scale characteristics of dust storms, but reliable records of dust are generally on the scale of a decade or less. Here the authors develop a simple model for using modern and historical data from meteorological satellites, in conjunction with a proxy record for atmospheric dust, to extend satellite-retrieved dust optical depth over the northern tropical Atlantic Ocean from 1955 to 2008. The resultant 54-yr record of dust has a spatial resolution of 1° and a monthly temporal resolution. From analysis of the historical dust data, monthly tropical northern Atlantic dust cover is bimodal, has a strong annual cycle, peaked in the early 1980s, and shows minimums in dustiness during the beginning and end of the record. These dust optical depth estimates are used to calculate radiative forcing and heating rates from the surface through the top of the atmosphere over the last half century. Radiative transfer simulations show a large net negative dust forcing from the surface through the top of the atmosphere, also with a distinct annual cycle, and mean tropical Atlantic monthly values of the surface forcing range from -3 to -9 W/m**2. Since the surface forcing is roughly a factor of 3 larger in magnitude than the top-of-the-atmosphere forcing, there is also a positive heating rate of the midtroposphere by dust.

Hydrological and meteorological records from the Vernagtferner Basin - Vernagtbach station, for the years 2002 to 2012

In November 2001, two separate Campbell loggers ("Meteologger" and "Hydrologger", both type CR23X) were installed at the Vernagtbach site in the Oetztal Alps, Austria (Latitude: 46.85; Longitude: 10.82; Elevation: 2640 m). On these loggers, 10-minutes centred averages for the meteorological data and 5-minutes centred averages for the hydrological data are recorded. The meteorological parameters comprise air temperature, humidity of the air, air pressure, four radiation components, wind direction and speed, precipitation and snow height. For air temperature, two records are published, recorded with a ventilated and an unventilated Pt-100 in a Stevenson screen; for precipitation, three time series are available: (I) the cumulative record of a weighing gauge for the whole year, (II) single events derived from (I), and (III) single events from a tipping bucket; (II) and (III) are only provided for the period 1, May to 31, October of each year. Wind records are also given with a time step of one hour, as only these records include several statistics of speed and direction. Hydrological parameters are recorded on the "Hydrologger", they comprise water stage, discharge, water temperature and electrolytic conductivity of the water. An identifying number gives the kind of instrument used in the water stage time series. Daily photographs of the glacier are provided and analysed with respect to precipitation type.

Sources and seasonality of polycyclic aromatic hydrocarbons transported to Alert, Canadian Arctic

A probabilistic function (integrated source contribution function, ISCF) based on backward air mass trajectory calculation was developed to track sources and atmospheric pathways of polycyclic aromatic hydrocarbons (PAHs) to the Canadian High Arctic station of Alert. In addition to the movement of air masses, the emission intensities at the sources and the major processes of partition, indirect photolysis, and deposition occurring on the way to the Arctic were incorporated into the ISCF. The predicted temporal trend of PAHs at Alert was validated by measured PAH concentrations throughout 2004. The PAH levels in the summer are orders of magnitude lower than those in the winter and spring when long-range atmospheric transport events occur more frequently. PAHs observed at Alert are mostly from East Asia (including Russia Far East), North Europe (including European Russia), and North America. These sources account for 25, 45, and 27% of PAHs atmospheric level at Alert, respectively. Source regions and transport pathways contributing to the PAHs contamination in the Canadian High Arctic vary seasonally. In the winter, Russia and Europe are the major sources. PAHs from these sources travel eastward and turn to the north at approximately 120°E before reaching Alert, in conjunction with the well- known Arctic haze events. In the spring, PAHs from Russia and Europe first migrate to the west and then turn to the north at 60°W toward Alert. The majority of PAHs in the summer are from northern Canada where they are carried to Alert via low- level transport pathways. In the fall, 70% of PAHs arriving at Alert are delivered from North American sources.