On the effect of decreasing CO2 concentration in the atmosphere

In the present paper the effect of an abrupt change of the atmospheric radiative forcing is investigated by means of a global climate model that includes a mixed layer ocean. In assessing if, under such a change, the model response has a bifurcation point, the steady solution is studied for a sudden decrease of CO₂ concentration from its actual value. It is found that there is a critical threshold for CO₂ content below which the model ends up to a snowball Earth. It occurs for a few percentage changes of CO₂ concentration around the threshold because the model strongly depends on the relationship among atmospheric temperature, water vapor content and the sudden ice-albedo feedback activation, even in the subtropical regions. Moreover, results suggest that the transition to ice-covered Earth is clearly favoured when Q-flux corrections (i.e. the parameterization of ocean heat transports) are removed.     

Precipitation climatology over India: validation with observations and reanalysis datasets and spatial trends

Changing rainfall patterns have significant effect on water resources, agriculture output in many countries, especially the country like India where the economy depends on rain-fed agriculture. Rainfall over India has large spatial as well as temporal variability. To understand the variability in rainfall, spatial–temporal analyses of rainfall have been studied by using 107 (1901–2007) years of daily gridded India Meteorological Department (IMD) rainfall datasets. Further, the validation of IMD precipitation data is carried out with different observational and different reanalysis datasets during the period from 1989 to 2007. The Global Precipitation Climatology Project data shows similar features as that of IMD with high degree of comparison, whereas Asian Precipitation-Highly-Resolved Observational Data Integration Towards Evaluation data show similar features but with large differences, especially over northwest, west coast and western Himalayas. Spatially, large deviation is observed in the interior peninsula during the monsoon season with National Aeronautics Space Administration-Modern Era Retrospective-analysis for Research and Applications (NASA-MERRA), pre-monsoon with Japanese 25 years Re Analysis (JRA-25), and post-monsoon with climate forecast system reanalysis (CFSR) reanalysis datasets. Among the reanalysis datasets, European Centre for Medium-Range Weather Forecasts Interim Re-Analysis (ERA-Interim) shows good comparison followed by CFSR, NASA-MERRA, and JRA-25. Further, for the first time, with high resolution and long-term IMD data, the spatial distribution of trends is estimated using robust regression analysis technique on the annual and seasonal rainfall data with respect to different regions of India. Significant positive and negative trends are noticed in the whole time series of data during the monsoon season. The northeast and west coast of the Indian region shows significant positive trends and negative trends over western Himalayas and north central Indian region.     

Zonal jets and cyclone–anticyclone asymmetry in decaying rotating turbulence: laboratory experiments and numerical simulations

The problem of zonal jet formation and cyclone–anticyclone asymmetry in decaying rotating turbulence is addressed using both laboratory experiments and numerical simulations with a high-resolution shallow water model in a spherical geometry. Experiments are performed at different Rossby and Froude numbers and applying a rigid wall as meridional boundary in the numerical scheme to mimic the experimental apparatus. The formation of a zonally banded flow pattern, i.e. meridionally confined easterly/westerly jets, has observed; both experimental and numerical results confirmed that this tendency is favoured by high-planetary vorticity gradients. Also, in the experiments characterized by large rotation speeds and small Rossby deformation radius, an initial symmetric distribution of relative vorticity is found to evolve towards a dominance of anticyclonic structures, indicating a breaking of the cyclone–anticyclone symmetry. This aspect has deepened by numerically analysing the sensitivity of the temporal variations of the asymmetry index with respect to the position of the meridional confinement as well as the effect of relaxing the divergence of the fluid (i.e. non-divergent case) to zero. Results suggested that experiments characterized by the higher rotation speed and the lower fluid thickness are better reproduced by a divergent model with a high-latitude meridional boundary.     

Ground-based GPS measurements: time behavior from half-hour to years

Ground-based GPS and weather stations time series for the period 2010–2012 of precipitable water vapor (PWV), relative humidity (RH), and surface temperature (T) of half-hourly resolution are analyzed to demonstrate their value for dynamical analyses and weather forecasting. Three sample stations in the USA from the SoumiNet network are considered, which have rather continuous data for the last 3 years and a few missing values. Results for the three stations reveal the following features: (1) PWV time behavior is dominated by the annual cycle superimposed on high-frequency fluctuations with missing daily cycle, indicating a prevailing large-scale transport source of precipitable water at these sites; (2) RH is characterized by the daily cycle and high-frequency variability, while the annual cycle is missing; (3) T mainly varies following the annual and diurnal cycles; and (4) all variables show similar scaling properties of their variance spectra, S(f)?～?f ^–β , with a high-frequency regime of red noise type scaling (β?～?2) up to a day and long-term persistence beyond a week (β?～?0.5), with a week-long frequency interval of transition. Detrended fluctuation analysis of relative humidity indicates a clear long-term persistence scaling covering more than three decades. Implications of these findings on weather forecasting and climate modeling are discussed.     

Spatial patterns and temporal trends of daily precipitation indices in Iran

Spatial patterns of daily precipitation indices and their temporal trends over Iran are investigated using the APHRODITE gridded daily precipitation dataset for the period 1961–2004. The performance and limitations of the gridded dataset are checked against observations at ten rain-gauge stations that are representative of different climates in Iran. Results suggest that the spatial patterns of the indices reflect the role of orography and sea neighborhoods in differentiating central-southern arid and semi-arid regions from northern and western mountainous humid areas. It is also found that western Iran is impacted by the most extreme daily precipitation events occurring in the country, though the number of rainy days has its maximum in the Caspian Sea region. The time series of precipitation indices is checked for long-term trends using the least squares method and Mann-Kendall test. The maximum daily precipitation per year shows upward trends in most of Iran, though being statistically significant only in western regions. In the same regions, upward trends are also observed in the number of wet days and in the accumulated precipitation and intensity during wet days. Conversely, the contribution of precipitation events below the 75th percentile to the annual total precipitation is decreasing with time, suggesting that extreme events are responsible for the upward trend observed in the total annual precipitation and in the other indices. This tendency towards more severe/extreme precipitation events, if confirmed by other datasets and further analyses with longer records, would require the implementation of adequate water resources management plans in western Iran aimed at mitigating the increasing risk of intense precipitation and associated flash floods and soil erosion.     

Fundamental Problems in Astrophysics

Progress of modern astrophysics requires the access to the electromagnetic spectrum in the broadest energy range. The Ultraviolet is a fundamental energy domain since it is one of the most powerful tool to study plasmas at temperatures in the 3,000–300,000 K range as well as electronic transitions of the most abundant molecules in the Universe. Moreover, the UV radiation field is a powerful astrochemical and photoionizing agent.The objective of this review is to describe the crucial issues that require access to the UV range. A summary has been added to the end with a more classic view of UV needs by astronomical object type; this approach is followed at length in the rest of the contributions of this issue.     

A new “tetrasporangial” species ofLiagora (Rhodophyta. Nemaliales) from Hawai’i

A new species ofLiagora, L. perennis sp. nov. from Hawai’i, is described. Unlike species of this genus in China, it is carpotetrasporangial, and at the place of expected carposporangia bears cruciately divided tetrasporangia, a detail which differentiates it from the usual species ofLiagora without tetraspores that have been reported in China. Notes are provided on otherLiagora species that have an impact on the taxonomy of species found in China. Dedicated to the memory of Zhang Junfu(C. F. Chang) whose studies on marine algae I respect highly, and whose good-humored friendship I treasure.     

Key problems in cool-star astrophysics

Selected key problems in cool-star astrophysics are reviewed, with emphasis on the importance of new ultraviolet missions to tackle the unresolved issues.UV spectral signatures are an essential probe of critical physical processes related to the production and transport of magnetic energy in astrophysical plasmas ranging, for example, from stellar coronae, to the magnetospheres of magnetars, and the accretion disks of protostars and Active Galactic Nuclei. From an historical point of view, our comprehension of such processes has been closely tied to our understanding of solar/stellar magnetic activity, which has its origins in a poorly understood convection-powered internal magnetic dynamo. The evolution of the Sun's dynamo, and associated magnetic activity, affected the development of planetary atmospheres in the early solar system, and the conditions in which life arose on the primitive Earth. The gradual fading of magnetic activity as the Sun grows old likewise will have profound consequences for the future heliospheric environment. Beyond the Sun, the magnetic activity of stars can influence their close-in companions, and vice versa.Cool star outer atmospheres thus represent an important laboratory in which magnetic activity phenomena can be studied under a wide variety of conditions, allowing us to gain insight into the fundamental processes involved. The UV range is especially useful for such studies because it contains powerful diagnostics extending from warm (∼ 10⁴ K) chromospheres out to hot (1–10 MK) coronae, and very high-resolution spectroscopy in the UV has been demonstrated by the GHRS and STIS instruments on HST but has not yet been demonstrated in the higher energy EUV and X-ray bands. A recent example is the use of the hydrogen Lyα resonance line—at 110 000 resolution with HST STIS—study, for the first time, coronal winds from cool stars through their interaction with the interstellar gas. These winds cannot be detected from the ground, for lack of suitable diagnostics; or in the X-rays, because the outflowing gas is too thin.A 2m class UV space telescope with high resolution spectroscopy and monitoring capabilities would enable important new discoveries in cool-star astronomy among the stars of the solar neighborhood out to about 150 pc. A larger aperture facility (4–6 m) would reach beyond the 150 pc horizon to fainter objects including young brown dwarfs and pre-main sequence stars in star-forming regions like Orion, and magnetic active stars in distant clusters beyond the Pleiades and α Persei. This would be essential, as well, to characterize the outer atmospheres of stars with planets, that will be discovered by future space missions like COROT, Kepler, and Darwin.Deceased October 23, 2005     

Evidence for a massive dark object in NGC 4350

In this work we build a detailed dynamic model for an S0 galaxy possibly hosting a central massive dark object (MDO). We show that the photometric profiles and the kinematics along the major and minor axes, including the h ₃ and h ₄ profiles, imply the presence of a central MDO of mass     i.e. 0.3–2.8 per cent of the mass derived for the stellar spheroidal component. Models without MDO are unable to reproduce the kinematic properties of the inner stars and of the rapidly rotating nuclear gas.
The stellar population consists of an exponential disc (27 per cent of the light) and a diffuse spheroidal component (73 per cent of the light) that cannot be represented by a simple de Vaucouleurs profile at any radius. The M L ratios we found for the stellar components (3.3 and 6.6 respectively) are typical of those of disc and elliptical galaxies.     

Messinian events in the Black Sea

Past hydrological interactions between the Mediterranean Sea and Black Sea are poorly resolved due to complications in establishing a high‐resolution time frame for the Black Sea. We present a new greigite‐based magnetostratigraphic age model for the Mio‐Pliocene deposits of DSDP Hole 380/380A, drilled in the southwestern Black Sea. This age model is complemented by ⁴⁰Ar/³⁹Ar dating of a volcanic ash layer, allowing a direct correlation of Black Sea deposits to the Messinian salinity crisis (MSC) interval of the Mediterranean Sea. Proxy records divide these DSDP deposits into four intervals: (i) Pre‐MSC marine conditions (6.1–6.0 Ma); (ii) highstand, fresh to brackish water conditions (~6.0–5.6 Ma); (iii) lowstand, fresh‐water environment (5.6–5.4 Ma) and (iv) highstand, fresh‐water conditions (5.4–post 5.0 Ma). Our results indicate the Black Sea was a major fresh‐water source during gypsum precipitation in the Mediterranean Sea. The introduction of Lago Mare fauna during the final stage of the MSC coincides with a sea‐level rise in the Black Sea. Across the Mio‐Pliocene boundary, sea‐level and salinity in the Black Sea did not change significantly.