Anomalously deep convection in the Irminger Sea during the winter of 2014–2015

The anomalous thermohaline properties of the core of the Labrador Sea water (LSW), a product of winter convection resulted from the ocean–winter interaction, which were recorded in the Irminger Sea in 2014 and 2015, are discussed. It is found that, in the summer of 2015, the LSW filled the entire deepwater basin in the south of the sea down to a depth of 1300 m over the periphery of the Irminger gyral, and down to a depth of 1800 m, in the anticyclone eddy formed in early June of 2015. The maximum density of the LSW core here was 27.75 σ_θ. Such deep and intense winter convection in the Irminger Sea was last recorded 20 years ago. As a result, the temperature of the LSW dropped to values observed in the years 2002 and 2007, but its average salinity remained high. The LSW that have been formed in recent years are reported to have great amplitude and nonmonotonic variability of the properties.     

Climate patterns of short-wave solar radiation over oceans based on a new parameterization

The work describes the creation of a new global climatology of short-wave radiation incoming to the ocean surface; the climatology is based on a new parameterization of short-wave fluxes. Advantages of the new parameterization are allowance for nonlinearity of the dependence of the atmospheric transmission factor on the height of the Sun under a clear sky and allowance for different morphological types of clouds under the overcast. It is shown that taking into account these factors leads to substantial differences in short-wave radiation fluxes in comparison to existing parameterizations.     

Comparison of in-situ and satellite data of surface incoming short-wavelength radiation for the Atlantic Ocean during 2004–2014

Information about short-wavelength (from 0.2 to 4 μm) heat radiation fluxes incoming to the ocean surface is available from very few observations collected by shipboard equipment and buoys and obtained from satellite data archives. Presently, the most complete archive on short-wavelength radiation fluxes is provided by geostationary Earth-orbiting satellites, such as 1G and 2G МETEOSAT (European Union), GOES (United States) and HIMAWARI (Japan), which are equipped with scanners operating in the visible and infrared (IR) ranges, which can image the Earth’s disk every 0.5 h. Additionally, the European EPS/MetOP satellites and US NOAA satellites circulating in mid-altitude circumpolar Sun-synchronous orbits and carrying AVHRR radiometers [1] can be used to obtain daily and monthly average values of incoming short-wavelength solar radiation fluxes. In the future, radiation heat flux data measured by satellites will undoubtedly play a leading role; however, today, the available data record spans only the last few decades, still lacking accuracy and consequently requiring thorough validation.     

Subpolar mode water classes in the northeast Atlantic: Interannual and long-term variability

Doklady Earth Sciences - We distinguish the classes of Subpolar Mode Waters (SPMWs), calculate their long-term characteristics, and analyze their interannual and long-term variability based on data...     

An ERA40-based atmospheric forcing for global ocean circulation models

We develop, calibrate and test a dataset intended to drive global ocean hindcasts simulations of the last five decades. This dataset provides surface meteorological variables needed to estimate air-sea fluxes and is built from 6-hourly surface atmospheric state variables of ERA40. We first compare the raw fields of ERA40 to the CORE.v1 dataset of Large and Yeager (2004), used here as a reference, and discuss our choice to use daily radiative fluxes and monthly precipitation products extracted from satellite data rather than their ERA40 counterparts. Both datasets lead to excessively high global imbalances of heat and freshwater fluxes when tested with a prescribed climatological sea surface temperature. After identifying unrealistic time discontinuities (induced by changes in the nature of assimilated observations) and obvious global and regional biases in ERA40 fields (by comparison to high quality observations), we propose a set of corrections. Tropical surface air humidity is decreased from 1979 onward, representation of Arctic surface air temperature is improved using recent observations and the wind is globally increased. These corrections lead to a significant decrease of the excessive positive global imbalance of heat. Radiation and precipitation fields are then submitted to a small adjustment (in zonal mean) that yields a near-zero global imbalance of heat and freshwater. A set of 47-year-long simulations is carried out with the coarse-resolution (2° × 2°) version of the NEMO OGCM to assess the sensitivity of the model to the proposed corrections. Model results show that each of the proposed correction contributes to improve the representation of central features of the global ocean circulation.     

Short-Wave Radiation above the Ocean Based on Integral Parametrization and Satellite Data on the Amount of Cloud Cover

Doklady Earth Sciences - Satellite data on the total amount of cloud cover in integral parametrization of short-wave incoming fluxes to the Earth’s surface under mass calculations are...     

Cyclone life cycle characteristics over the Northern Hemisphere in coupled GCMs

Cyclone activity and life cycle are analysed in the coupled GCMs ECHAM5/OM and ECHAM4/OPYC3. First, the results for the present climate (1978–1999) are compared with ERA-40 and NCEP/NCAR reanalyses, showing a drastic improvement in the representation of cyclone activity in ECHAM5/OM compared to ECHAM4/OPYC3. The total number of cyclones, cyclone intensity, propagation velocity and deepening rates are found to be much more realistic in ECHAM5/OM relative to ECHAM4/OPYC3. Then, changes in extra tropical cyclone characteristics are compared between present day climate and future climate under the emission-scenario A1B using ECHAM5/OM. This comparison is performed using the 20-year time slices 1978–1999, 2070–2090 and 2170–2190, which were considered to be representative for the various climate conditions. The total number of cyclones does not undergo significant changes in a warmer climate. However, regional changes in cyclone numbers and frequencies are evident. One example is the Mediterranean region where the number of cyclones in summer increases almost by factor 2. Some noticeable changes are also found in cyclone life cycle characteristics (deepening rate and propagation velocity). Cyclones in the future climate scenario tend to move slower and their deepening rate becomes stronger, while cyclone intensity does not undergo significant change in a warmer climate. Generally, our results do not support the hypothesis of enhanced storminess under future climate conditions.     

Average annual structure and transport of waters eastward of Greenland by the system of western boundary currents

The results of calculating the values of average annual transport of waters eastward of Greenland in 2007–2015 by the system of western boundary currents are discussed. It is shown that the values of the average annual transport of waters estimated by different methods for measuring the velocity of currents and the different calculation methods differ by 20%. The role of friction in the bottom jets of the northwestern deep water, which were discovered for the first time during long-term observations, is discussed. The considerable contribution of the shelf water cascading across the continental slope to the formation of the structure and transport of the East Greenland Current is established. The significant influence of vertical mixing on the physicochemical properties of the bottom layer waters is shown. The biological arguments of the contribution made by the Irminger current and the subsurface waters to the formation of the northwestern deep water are presented.