Reduction of radiation biases by incorporating the missing cloud variability by means of downscaling techniques: a study using the 3-D MoCaRT model

Handling complexity to the smallest detail in atmospheric radiative transfer models is unfeasible in practice. On the one hand, the properties of the interacting medium, i.e., the atmosphere and the surface, are only available at a limited spatial resolution. On the other hand, the computational cost of accurate radiation models accounting for three-dimensional heterogeneous media are prohibitive for some applications, especially for climate modelling and operational remote-sensing algorithms. Hence, it is still common practice to use simplified models for atmospheric radiation applications. <br><br> Three-dimensional radiation models can deal with complex scenarios providing an accurate solution to the radiative transfer. In contrast, one-dimensional models are computationally more efficient, but introduce biases to the radiation results. <br><br> With the help of stochastic models that consider the multi-fractal nature of clouds, it is possible to scale cloud properties given at a coarse spatial resolution down to a higher resolution. Performing the radiative transfer within the cloud fields at higher spatial resolution noticeably helps to improve the radiation results. <br><br> We present a new Monte Carlo model, MoCaRT, that computes the radiative transfer in three-dimensional inhomogeneous atmospheres. The MoCaRT model is validated by comparison with the consensus results of the Intercomparison of Three-Dimensional Radiation Codes (I3RC) project. <br><br> In the framework of this paper, we aim at characterising cloud heterogeneity effects on radiances and broadband fluxes, namely: the errors due to unresolved variability (the so-called plane parallel homogeneous, PPH, bias) and the errors due to the neglect of transversal photon displacements (independent pixel approximation, IPA, bias). First, we study the effect of the missing cloud variability on reflectivities. We will show that the generation of subscale variability by means of stochastic methods greatly reduce or nearly eliminate the reflectivity biases. Secondly, three-dimensional broadband fluxes in the presence of realistic inhomogeneous cloud fields sampled at high spatial resolutions are calculated and compared to their one-dimensional counterparts at coarser resolutions. We found that one-dimensional calculations at coarsely resolved cloudy atmospheres systematically overestimate broadband reflected and absorbed fluxes and underestimate transmitted ones

Issues with fracturing ice during an ice drilling project in Greenland (EastGRIP)

Drilling an ice core through an ice sheet (typically 2000 to 3000 m thick) is a technical challenge that nonetheless generates valuable and unique information on palaeo-climate and ice dynamics. As technically the drilling cannot be done in one run, the core has to be fractured approximately every 3 m to retrieve core sections from the bore hole. This fracture process is initiated by breaking the core with core-catchers which also clamp the engaged core in the drill head while the whole drill is then pulled up with the winch motor. This standard procedure is known to become difficult and requires extremely high pulling forces (Wilhelms et al. 2007), in the very deep part of the drill procedure, close to the bedrock of the ice sheet, especially when the ice material becomes warm (approximately -2°C) due to the geothermal heat released from the bedrock. Recently, during the EastGRIP (East Greenland Ice coring Project) drilling we observed a similar issue with breaking off cored sections only with extremely high pulling forces, but started from approximately 1800 m of depth, where the temperature is still very cold (approximately -20°C). This has not been observed at other ice drilling sites. As dependencies of fracture behaviour on crystal orientation and grain size are known (Schulson & Duval 2009) for ice, we thus examined the microstructure in the ice samples close to and at the core breaks. First preliminary results suggest that these so far unexperienced difficulties are due to the profoundly different c-axes orientation distribution (CPO) in the EastGRIP ice core. In contrast to other deep ice cores which have been drilled on ice domes or ice divides, EastGRIP is located in an ice stream. This location means that the deformation geometry (kinematics) is completely different, resulting in a different CPO (girdle pattern instead of single maximum pattern). Evidence regarding additional grain-size dependence will hopefully help to refine the fracturing procedure, which is possible due to a rather strong grain size layering observed in natural ice formed by snow precipitation. --------------------- Wilhelms, F.; Sheldon, S. G.; Hamann, I. & Kipfstuhl, S. Implications for and findings from deep ice core drillings - An example: The ultimate tensile strength of ice at high strain rates. Physics and Chemistry of Ice (The proceedings of the International Conference on the Physics and Chemistry of Ice held at Bremerhaven, Germany on 23-28 July 2006), 2007, 635-639 Schulson, E. M. & Duval, P. Creep and Fracture of Ice. Cambridge University Press, 2009, 40

Corrigendum to "Water isotopic ratios from a continuously melted ice core sample" published in Atmos. Meas. Tech., 4, 2531–2542, 2011

No abstract available

NEEM seasonal dO18 data for "Climate information preserved in seasonal water isotope at NEEM: relationships with temperature, circulation and sea ice"

NEEM seasonal dO18 data over the period 1855-2004. Please cite the following reference when using the data: Zheng, M., Sjolte, J., Adolphi, F., Vinther, B. M., Steen-Larsen, H. C., Popp, T. J., and Muscheler, R.: Climate information preserved in seasonal water isotope at NEEM: relationships with temperature, circulation and sea ice, Climate of the Past, 14, 1067-1078, https://doi.org/10.5194/cp-14-1067-2018, 2018

The 8.2 ka event from Greenland ice cores

We present a collection of high-resolution chemistry and stable isotope records from the plateau of the Greenland ice cap during the cold event 8200 yr ago. Using a composite of four records, the cold event is observed as a 160.5 yr period during which decadal-mean isotopic values were below average, within which there is a central event of 69 yr during which values were consistently more than one standard deviation below the average for the preceding period. Four cores in north, south, and central Greenland show differences at decadal and shorter timescales; it is not yet clear if this represents significant spatial differences in response. The results show clear evidence for colder temperatures and a decrease in snow-accumulation rate. However, the changes in chemical concentrations for the ions looked at here are small, suggesting only minor changes in atmospheric circulation for this event. Apart from the decrease in methane concentration, Greenland ice cores give only weak evidence for effects outside the North Atlantic region

Stable isotopes in the atmospheric marine boundary layer water vapour over the Atlantic Ocean, 2012–2015

International audienc

High-resolution Greenland Ice Core data show abrupt climate change happens in few years

International audienc