Meridional transport and deposition of atmospheric 10Be

10Be concentrations measured in ice cores exhibit larger temporal variability than expected based on theoretical production calculations. To investigate whether this is due to atmospheric transport a general circulation model study is performed with the 10Be production divided into stratospheric, tropospheric tropical, tropospheric subtropical and tropospheric polar sources. A control run with present day 10Be production rate is compared with a run during a geomagnetic minimum. The present 10Be production rate is 4–5 times higher at high latitudes than in the tropics whereas during a period of no geomagnetic dipole field it is constant at all latitudes. The 10Be deposition fluxes, however, show a very similar latitudinal distribution in both the present day and the geomagnetic minimum run indicating that 10Be is well mixed in the atmosphere before its deposition. This is also confirmed by the fact that the contribution of 10Be produced in the stratosphere is dominant (55%–70%) and relatively constant at all latitudes. The contribution of stratospheric 10Be is approximately 70% in Greenland and 60% in Antarctica reflecting the weaker stratosphere-troposphere air exchange in the Southern Hemisphere

Modeling cosmogenic radionuclides 10Be and 7Be during the Maunder Minimum using the ECHAM5-HAM general circulation model

All existing 10Be records from Greenland and Antarctica show increasing concentrations during the Maunder Minimum period (MM), 1645–1715, when solar activity was very low and the climate was colder (little ice age). In detail, however, the 10Be records deviate from each other. We investigate to what extent climatic changes influence the 10Be measured in ice by modeling this period using the ECHAM5-HAM general circulation model. Production calculations show that during the MM the mean global 10Be production was higher by 32% than at present due to lower solar activity. Our modeling shows that the zonally averaged modeled 10Be deposition flux deviates by only ~8% from the average increase of 32%, indicating that climatic effects are much smaller than the production change. Due to increased stratospheric production, the 10Be content in the downward fluxes is larger during MM, leading to larger 10Be deposition fluxes in the subtropics, where stratosphere-troposphere exchange (STE) is strongest. In polar regions the effect is small. In Greenland the deposition change depends on latitude and altitude. In Antarctica the change is larger in the east than in the west. We use the 10Be/7Be ratio to study changes in STE. We find larger change between 20° N–40° N during spring, pointing to a stronger STE in the Northern Hemisphere during MM. In the Southern Hemisphere the change is small. These findings indicate that climate changes do influence the 10Be deposition fluxes, but not enough to significantly disturb the production signal. Climate-induced changes remain small, especially in polar regions

10Be in last deglacial climate simulated by ECHAM5-HAM – Part I: Climatological influences on 10Be deposition

Reconstruction of solar irradiance has only been possible for the Holocene so far. During the last deglaciation, two solar proxies (10Be and 14C) deviate strongly, both of them being influenced by climatic changes in a different way. This work addresses the climate influence on 10Be deposition by means of ECHAM5-HAM atmospheric aerosol–climate model simulations, forced by sea surface temperatures and sea ice extent created by the CSIRO Mk3L coupled climate system model. Three time slice simulations were performed during the last deglaciation: 10 000 BP ("10k"), 11 000 BP ("11k") and 12 000 BP ("12k"), each 30 yr long. The same, theoretical, 10Be production rate was used in each simulation to isolate the impact of climate on 10Be deposition. The changes are found to follow roughly the reduction in the greenhouse gas concentrations within the simulations. The 10k and 11k simulations produce a surface cooling which is symmetrically amplified in the 12k simulation. The precipitation rate is only slightly reduced at high latitudes, but there is a northward shift in the polar jet in the Northern Hemisphere, and the stratospheric westerly winds are significantly weakened. These changes occur where the sea ice change is largest in the deglaciation simulations. This leads to a longer residence time of 10Be in the stratosphere by 30 (10k and 11k) to 80 (12k) days, increasing the atmospheric concentrations (25–30% in 10k and 11k and 100% in 12k). Furthermore the shift of westerlies in the troposphere leads to an increase of tropospheric 10Be concentrations, especially at high latitudes. The contribution of dry deposition generally increases, but decreases where sea ice changes are largest. In total, the 10Be deposition rate changes by no more than 20% at mid- to high latitudes, but by up to 50% in the tropics. We conclude that on "long" time scales (a year to a few years), climatic influences on 10Be deposition remain small (less than 50%) even though atmospheric concentrations can vary significantly. Averaged over a longer period, all 10Be produced has to be deposited by mass conservation. This dominates over any climatic influences on 10Be deposition. Snow concentrations, however, do not follow mass conservation and can potentially be impacted more by climate due to precipitation changes. Quantifying the impact of deglacial climate modulation on 10Be in terms of preserving the solar signal locally is analysed in an accompanying paper (Heikkilä et al., 10Be in late deglacial climate simulated by ECHAM5-HAM – Part 2: Isolating the solar signal from 10Be deposition). © Author(s) 2013

Cosmogenic Radionuclides as an Extension of the Neutron Monitor Era into the Past: Potential and Limitations

The cosmogenic radionuclides, 10Be, 14C and others, provide a record of the paleo-cosmic radiation that extends >10,000 years into the past. They are the only quantitative means at our disposal to study the heliosphere prior to the commencement of routine sunspot observations in the 17th century. The cosmogenic radionuclides are primarily produced by secondary neutrons generated by the galactic cosmic radiation, and can be regarded, in a sense, as providing an extrapolation of the neutron monitor era into the past. However, their characteristics are quite different from the man-made neutron monitor in several important respects: (1)they are sensitive to somewhat lower cosmic ray energies; (2)their temporal resolution is ∼1 to 2 years, being determined by the rapidity with which they are sequestered in ice, biological, or other archives; (3)the statistical precision for annual data is very poor (∼19%); however it is quite adequate (∼5% for 22-year averages) to study the large variations (±40%) that have occurred in the paleo-cosmic ray record in the past between grand solar minima and maxima. The data contains "noise” caused by local meteorological effects, and longer-term climate effects, and the use of principal component analysis to separate these "system” effects from production effects is outlined. The concentrations of 10Be decreased by a factor of two at the commencement of Holocene, the present-day "interglacial”, due to a 100% increase in the ice accumulation rates in polar regions. The use of the 10Be flux to study heliospheric properties during the last glacial is discussed briefl

Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM

A diagnostic cloud nucleation scavenging scheme, which determines stratiform cloud scavenging ratios for both aerosol mass and number distributions, based on cloud droplet, and ice crystal number concentrations, is introduced into the ECHAM5-HAM global climate model. This scheme is coupled with a size-dependent in-cloud impaction scavenging parameterization for both cloud droplet-aerosol, and ice crystal-aerosol collisions. The aerosol mass scavenged in stratiform clouds is found to be primarily (>90%) scavenged by cloud nucleation processes for all aerosol species, except for dust (50%). The aerosol number scavenged is primarily (>90%) attributed to impaction. 99% of this impaction scavenging occurs in clouds with temperatures less than 273 K. Sensitivity studies are presented, which compare aerosol concentrations, burdens, and deposition for a variety of in-cloud scavenging approaches: prescribed fractions, a more computationally expensive prognostic aerosol cloud processing treatment, and the new diagnostic scheme, also with modified assumptions about in-cloud impaction and nucleation scavenging. Our results show that while uncertainties in the representation of in-cloud scavenging processes can lead to differences in the range of 20–30% for the predicted annual, global mean aerosol mass burdens, and near to 50% for accumulation mode aerosol number burden, the differences in predicted aerosol mass concentrations can be up to one order of magnitude, particularly for regions of the middle troposphere with temperatures below 273 K where mixed and ice phase clouds exist. Different parameterizations for impaction scavenging changed the predicted global, annual mean number removal attributed to ice clouds by seven-fold, and the global, annual dust mass removal attributed to impaction by two orders of magnitude. Closer agreement with observations of black carbon profiles from aircraft (increases near to one order of magnitude for mixed phase clouds), mid-troposphere <sup>210</sup>Pb vertical profiles, and the geographic distribution of aerosol optical depth is found for the new diagnostic scavenging scheme compared to the prescribed scavenging fraction scheme of the standard ECHAM5-HAM. The diagnostic and prognostic schemes represent the variability of scavenged fractions particularly for submicron size aerosols, and for mixed and ice phase clouds, and are recommended in preference to the prescribed scavenging fractions method

Detecting Current Noise with a Josephson Junction in the Macroscopic Quantum Tunneling Regime

We discuss the use of a hysteretic Josephson junction to detect current fluctuations with frequencies below the plasma frequency of the junction. These adiabatic fluctuations are probed by switching measurements observing the noise-affected average rate of macroscopic quantum tunneling of the detector junction out of its zero-voltage state. In a proposed experimental scheme, frequencies of the noise are limited by an on-chip filtering circuit. The third cumulant of current fluctuations at the detector is related to an asymmetry of the switching rates.Comment: 26 pages, 10 figures. To appear in Journal of Low Temperature Physics in the proceedings of the ULTI conference organized in Lammi, Finland (2006

Submillimeter Line Emission from LMC 30Dor: The Impact of a Starburst on a Low Metallicity Environment

(Abridged) The 30 Dor region in the Large Magellanic Cloud (LMC) is the most vigorous star-forming region in the Local Group. Star formation in this region is taking place in low-metallicity molecular gas that is exposed to an extreme far--ultraviolet (FUV) radiation field powered by the massive compact star cluster R136. We used the NANTEN2 telescope to obtain high-angular resolution observations of the 12CO 4-3, 7-6, and 13CO 4-3 rotational lines and [CI] 3P1-3P0 and 3P2-3P1 fine-structure submillimeter transitions in 30Dor-10, the brightest CO and FIR-emitting cloud at the center of the 30Dor region. We derived the properties of the low-metallicity molecular gas using an excitation/radiative transfer code and found a self-consistent solution of the chemistry and thermal balance of the gas in the framework of a clumpy cloud PDR model. We compared the derived properties with those in the N159W region, which is exposed to a more moderate far-ultraviolet radiation field compared with 30Dor-10, but has similar metallicity. We also combined our CO detections with previously observed low-J CO transitions to derive the CO spectral-line energy distribution in 30Dor-10 and N159W. The separate excitation analysis of the submm CO lines and the neutral carbon fine structure lines shows that the mid-J CO and [CI]-emitting gas in the 30Dor-10 region has a temperature of about 160 K and a H2 density of about 10^4 cm^-3. We find that the molecular gas in 30Dor-10 is warmer and has a lower beam filling factor compared to that of N159W, which might be a result of the effect of a strong FUV radiation field heating and disrupting the low--metallicity molecular gas. We use a clumpy PDR model (including the [CII] line intensity reported in the literature) to constrain the FUV intensity to about chi_0 ~ 3100 and an average total H density of the clump ensemble of about 10^5 cm^-3 in 30Dor-10.Comment: 11 pages, 8 figures. Accepted for publication in A&

Microwave amplification with nanomechanical resonators

Sensitive measurement of electrical signals is at the heart of modern science and technology. According to quantum mechanics, any detector or amplifier is required to add a certain amount of noise to the signal, equaling at best the energy of quantum fluctuations. The quantum limit of added noise has nearly been reached with superconducting devices which take advantage of nonlinearities in Josephson junctions. Here, we introduce a new paradigm of amplification of microwave signals with the help of a mechanical oscillator. By relying on the radiation pressure force on a nanomechanical resonator, we provide an experimental demonstration and an analytical description of how the injection of microwaves induces coherent stimulated emission and signal amplification. This scheme, based on two linear oscillators, has the advantage of being conceptually and practically simpler than the Josephson junction devices, and, at the same time, has a high potential to reach quantum limited operation. With a measured signal amplification of 25 decibels and the addition of 20 quanta of noise, we anticipate near quantum-limited mechanical microwave amplification is feasible in various applications involving integrated electrical circuits.Comment: Main text + supplementary information. 14 pages, 3 figures (main text), 18 pages, 6 figures (supplementary information

Reconstruction and simulation of an extreme flood event in the Lago Maggiore catchment in 1868

Heavy precipitation on the south side of the central Alps produced a catastrophic flood in October 1868. We assess the damage and societal impacts, as well as the atmospheric and hydrological drivers using documentary evidence, observations and novel numerical weather and runoff simulations.The greatest damage was concentrated close to the Alpine divide and Lago Maggiore. An atmospheric reanalysis emphasizes the repeated occurrence of streamers of high potential vorticity as precursors of heavy precipitation. Dynamical downscaling indicates high freezing levels (4000&thinsp;m&thinsp;a.s.l.), extreme precipitation rates (max. 270&thinsp;mm&thinsp;24&thinsp;h−1) and weather dynamics that agree well with observed precipitation and damage, and with existing concepts of forced low-level convergence, mid-level uplift and iterative northeastward propagation of convective cells. Simulated and observed peak levels of Lago Maggiore differ by 2&thinsp;m, possibly because the exact cross section of the lake outflow is unknown. The extreme response of Lago Maggiore cannot be attributed to low forest cover. Nevertheless, such a paradigm was adopted by policy makers following the 1868 flood, and used to implement nationwide afforestation policies and hydraulic structures.These findings illustrate the potential of high-resolution, hydrometeorological models – strongly supported by historical methods – to shed new light on weather events and their socio-economic implications in the 19th century.</p

Evolutionary impact assessment: accounting for evolutionary consequences of fishing in an ecosystem approach to fisheries management

Managing fisheries resources to maintain healthy ecosystems is one of the main goals of the ecosystem approach to fisheries (EAF). while the number of international treaties call for the implementation of EAF, there are still gaps in the underlying methodology. One aspect that has received substantial scientific attention recently in fisheries-induced evolution (FIE). Increasing evidence indicates that intensive fishing has the potential to exert strong directional selection on life-history traits, behavior, physiology, and morphology of exploited fish. Of particular concern is that reversing evolutionary responses to fishing can be much more difficult than reversing demographic or phenotypically plastic responses. Furthermore, like climate change, multiple agents cause fisheries-induced evolution with effects accumulating over time. Consequently, FIE may alter then utility derived from fish stocks, which in turn can modify the monetary value living aquatic resources provide to society. Quantifying and predicting the evolutionary effects of fishing is therefore important for both ecological and economic reasons, An important reason this is not happening is the lack of an appropriate assessment framework. We therefor describe the evolutionary impact assessment (EvoIA) as a structured approach for assessing the evolutionary outcomes of alternative management options. EvoIA can contribute to the ecosystem approach to fisheries management by clarifying how evolution may alter stock properties and ecological relations, support the precautionary approach to fisheries management by addressing a previously overlooked source of uncertainty and risk, and thus contribute to sustainable fisheries