Variability of daily winter wind speed distribution over Northern Europe during the past millennium in regional and global climate simulations

We analyse the variability of the probability distribution of daily wind speed in wintertime over Northern and Central Europe in a series of global and regional climate simulations covering the last centuries, and in reanalysis products covering approximately the last 60 years. The focus of the study lies on identifying the link of the variations in the wind speed distribution to the regional near-surface temperature, to the meridional temperature gradient and to the North Atlantic Oscillation. Our main result is that the link between the daily wind distribution and the regional climate drivers is strongly model dependent. The global models tend to behave similarly, although they show some discrepancies. The two regional models also tend to behave similarly to each other, but surprisingly the results derived from each regional model strongly deviates from the results derived from its driving global model. In addition, considering multi-centennial timescales, we find in two global simulations a long-term tendency for the probability distribution of daily wind speed to widen through the last centuries. The cause for this widening is likely the effect of the deforestation prescribed in these simulations. We conclude that no clear systematic relationship between the mean temperature, the temperature gradient and/or the North Atlantic Oscillation, with the daily wind speed statistics can be inferred from these simulations. The understand- ing of past and future changes in the distribution of wind speeds, and thus of wind speed extremes, will require a detailed analysis of the representation of the interaction between large-scale and small-scale dynamics.

Modern sea surface productivity and temperature estimations off Chile as detected by coccolith accumulation rates

Recent coccoliths from 74 surface sediment samples recovered from the southeastern Pacific off Chile were examined quantitatively to investigate modern regional gradients of sea surface productivity and temperature. All findings are based on coccolith accumulation rates. Therefore an approach was designed to estimate recent sedimentation rates based on 210Pb and bulk chemistry analyses of the same set of surface samples. Highest total coccolith accumulation rates were found off north-central Chile, where seasonal upwelling takes place. Based on a multiple linear regression between calculated coccolith accumulation rates and World Ocean Atlas derived sea surface temperatures, a calibration model to reconstruct annual average temperatures of the uppermost 75 m of the water column is provided. The model was cross-validated and the SST estimates were compared with SST observed and SST estimates based on diatoms and planktonic foraminifera, showing a good correlation.

Investigating the sensitivity of hurricane intensity and trajectory to sea surface temperatures using the regional model WRF

The influence of sea surface temperature (SST) anomalies on the hurricane characteristics are investigated in a set of sensitivity experiments employing the Weather Research and Forecasting (WRF) model. The idealised experiments are performed for the case of Hurricane Katrina in 2005. The first set of sensitivity experiments with basin-wide changes of the SST magnitude shows that the intensity goes along with changes in the SST, i.e., an increase in SST leads to an intensification of Katrina. Additionally, the trajectory is shifted to the west (east), with increasing (decreasing) SSTs. The main reason is a strengthening of the background flow. The second set of experiments investigates the influence of Loop Current eddies idealised by localised SST anomalies. The intensity of Hurricane Katrina is enhanced with increasing SSTs close to the core of a tropical cyclone. Negative nearby SST anomalies reduce the intensity. The trajectory only changes if positive SST anomalies are located west or north of the hurricane centre. In this case the hurricane is attracted by the SST anomaly which causes an additional moisture source and increased vertical winds.

Eemian and Holocene sea-surface conditions in the southern Black Sea: organic-walled dinoflagellate cyst record from core 22-GC3

In order to compare the sea-surface conditions in the Black Sea during the Holocene and Eemian, sapropelic parts of marine core 22-GC3 (42°13.53′N/36°29.55′E, 838 m water depth) were studied for organic-walled dinoflagellate cyst content. The record shows a change from freshwater/brackish assemblages (Pyxidinopsis psilata, Spiniferites cruciformis, and Caspidinium rugosum) to more marine assemblages (Lingulodinium machaerophorum and Spiniferites ramosus complex) during each interglacial, due to the inflow of saline Mediterranean water. The lacustrine–marine transitions in 22-GC3 occurred at ~ 8.3 cal kyr BP during the early Holocene and ~ 128 kyr BP during the early Eemian, slightly later compared to the onset of interglacial conditions on the adjacent land. Dinoflagellate cyst assemblages reveal higher sea-surface salinity (~ 28–30) (e.g. Spiniferites pachydermus, Bitectatodinium tepikiense, and Spiniferites mirabilis) around ~ 126.5–121 kyr BP in comparison to the Holocene (~ 15–20) as well as relatively high sea-surface temperature (e.g. Tuberculodinium vancampoae, S. pachydermus, and S. mirabilis) especially at ~ 127.6–125.3 kyr BP. Establishment of high sea-surface salinity during the Eemian correlates very well with reconstructed relatively high global sea-level and is explained as a combined effect of increased Mediterranean supply and high temperatures at the beginning of the last interglacial. The observed changes in the dinocyst record highlight the importance of nutrients for the composition of the Eemian and Holocene dinocyst assemblages.

Sea surface temperature and sea ice variability in the subpolar North Atlantic from explosive volcanism of the late thirteenth century

In this study, we use IP and alkenone biomarker proxies to document the subdecadal variations of sea ice and sea surface temperature in the subpolar North Atlantic induced by the decadally paced explosive tropical volcanic eruptions of the second half of the thirteenth century. The short- and long-term evolutions of both variables were investigated by cross analysis with a simulation of the IPSL-CM5A LR model. Our results show short-term ocean cooling and sea ice expansion in response to each volcanic eruption. They also highlight that the long response time of the ocean leads to cumulative surface cooling and subsurface heat buildup due to sea ice capping. As volcanic forcing relaxes, the surface ocean rapidly warms, likely amplified by subsurface heat, and remains almost ice free for several decades

Chandrayaan-1 observations of backscattered solar wind protons from the lunar regolith: Dependence on the solar wind speed

We study the backscattering of solar wind protons from the lunar regolith using the Solar Wind Monitor of the Sub-keV Atom Reflecting Analyzer on Chandrayaan-1. Our study focuses on the component of the backscattered particles that leaves the regolith with a positive charge. We find that the fraction of the incident solar wind protons that backscatter as protons, i.e., the proton-backscattering efficiency, has an exponential dependence on the solar wind speed that varies from ~0.01% to ~1% for solar wind speeds of 250 km/s to 550 km/s. We also study the speed distribution of the backscattered protons in the fast (~550 km/s) solar wind case and find both a peak speed at ~80% of the solar wind speed and a spread of ~85 km/s. The observed flux variations and speed distribution of the backscattered protons can be explained by a speed-dependent charge state of the backscattered particles.