Variability of Ocean Features and their Impact on Cyclogenesis over Arabian Sea During Post Monsoon Season

Arabian Sea (AS), the western sector of North Indian Ocean (NIO) produce smaller number of tropical cyclones as compared to Bay of Bengal. Though limited in numbers, the cyclones over Arabian sea are catastrophic by character. This make west coast of Indian subcontinent vulnerable to these hazards. The post-monsoon cyclogenesis over this region is known to be modulated by both monsoon rainfall and the El-Niño accompanied with positive Indian Ocean Dipole events. No single phenomena, however, can fully explain the variability observed in AS region. In this study, it is observed that apart from several known atmospheric forcings, inter-annual variability of ocean heat content (OHC) influence the post-monsoon AS cyclogenesis. The OHC of this region is partially modulated by the changes in salinity. Heat exchanges between the South West Indian Ocean (SWIO) and AS also modulates the OHC over AS. This remote influence is facilitated largely by the variability in the equatorial currents. Further it is seen that the recent trend of increased OHC post-2011 matches with the enhanced sea surface carbon over AS.

Arctic MIZ Sensitivity to Atmosphere- Ice-Ocean Feedbacks

<p><span>Over the past few decades, as the summer Arctic sea ice cover has been shrinking, the marginal ice zone (MIZ) has been widening. Projections indicate that the majority of the sea ice cover will become marginal (here defined as that region with ice area fractions between 0.15 and 0.8) over the next few decades. The impact of the change in atmospheric forcings on the sea ice cover and MIZ between the 1980s and the 2010s is evaluated using a coupled sea ice (CICE)-mixed layer model, that includes a prognostic floe size-thickness distribution (FSD) model. As the MIZ accounts for a greater fraction of the sea ice cover, some feedbacks with the atmosphere and ocean are expected to strengthen. The role of sea ice feedbacks with the atmosphere and ocean in response to the change in atmospheric conditions between the 1980s to the 2010s are evaluated using feedback denial simulations. In particular: i) the albedo feedback; ii) feedbacks associated with changes to mixed layer stratification (including changes in mixed layer properties) and therefore the ocean heat flux to the sea ice; and iii) changes to the lateral melt rate due to decreasing floe sizes.</span> </p>

Circulation patterns in northwest mediterranean harbours based on their geometric characteristics.

<p>This paper analyses the summer water circulation in Barcelona, Tarragona and Castellón harbours (east and north-east of Spain), based on field data acquired between April and September 2019. These data include information of wind, waves, 1DV currents, temperature and salinity parameters. The research characterizes the hydrodynamics at the mouth of each harbour and allows to estimate circulation patterns according to its physical characteristics. The availability of simultaneous data on the three harbours allows to analyse and study possible differences. The results show a two-layer circulation in all the harbours. In the cases of Tarragona and Castellón, both with a single mouth, the surface layer flows out of the harbour and the bottom currents circulate inwards. This pattern is reversed in the Barcelona harbour, which has two mouths and is more influenced by the local winds, affecting the distribution of currents in the water column. The bottom water temperature reveals significative differences between the three harbours, especially during the first half of the summer. The results suggest that sea level effects and the water exchange between the harbour and open-sea strongly determine the bottom water temperature. Nevertheless, the sea level series are different in the three harbours. In Barcelona and Tarragona, the meteorological tides are more affected by the atmospheric pressure changes; however, in the case of Castellón, which is smaller, the main influence is associated with the wind, which displaces water and causes a convergence when finding land that results in an increase in sea level. Therefore, the results reveal the importance of knowing the dimensions and morphology of each harbour to describe correctly its hydrodynamics because, despite being under comparable climatic conditions due to their geographical proximity, different hydrodynamic responses are observed to similar atmospheric forcings. The low intensities of the currents and the geometric complexity of the harbour domains, compared to open waters, imply that operational forecasting in these domains can present considerable uncertainties if they are not combined with field data.</p>

Estimation of water table, soil states and parameters of integrated subsurface-land surface models by data assimilation

<p>Estimating states and fluxes of the water cycle with terrestrial system models needs a large amount of input data, including soil and vegetation parameters, resulting in large uncertainties in model predictions. Assimilation of pressure head and/or soil moisture data can better constrain states and parameters of a terrestrial system model. Here we assimilate pressure head data and soil moisture data in a terrestrial system model over the Neckar catchment (13928 km<sup>2</sup>) with a spatial horizontal resolution of 800 m. We use the Terrestrial System Modeling Platform (TSMP), which consists of an atmospheric model component (not used in this work), the Community Land Model version 3.5 (CLM3.5), and the subsurface hydrological model Parflow, coupled by OASIS. TSMP is coupled to the Parallel Data Assimilation Framework (PDAF), which allows the assimilation of land surface and subsurface observations to estimate the model states and parameters. In this work the localized Ensemble Kalman Filter (LEnKF) was used to update hydraulic head, soil moisture and/or saturated hydraulic conductivity by assimilating hydraulic head or in situ soil moisture observations for a period of one year. Ensembles of soil properties, leaf area index and atmospheric forcings were generated. The ensemble of atmospheric forcings considered correlations among four variables, and spatio-temporal correlations of the atmospheric variables using a geostatistical procedure. The characterization of the water table depth and river discharge without data assimilation and for different scenarios of pressure head and soil moisture data assimilation were compared.</p>

An explicit estimate of the atmospheric nutrient impact on global oceanic productivity

State-of-the-art global nutrient deposition fields are coupled here to the Pelagic Interactions Scheme for Carbon and Ecosystem Studies (PISCES) biogeochemistry model to investigate their effect on ocean biogeochemistry in the context of atmospheric forcings for pre-industrial, present, and future periods. PISCES, as part of the European Community Earth system model (EC-Earth) model suite, runs in offline mode using prescribed dynamical fields as simulated by the Nucleus for European Modelling of the Ocean (NEMO) ocean model. Present-day atmospheric deposition fluxes of inorganic N, Fe, and P into the global ocean account for ∼ 40 Tg N yr−1, ∼ 0.28 Tg Fe yr−1, and ∼ 0.10 Tg P yr−1. Pre-industrial atmospheric nutrient deposition fluxes are lower compared to the present day (∼ 51 %, ∼ 36 %, and ∼ 40 % for N, Fe, and P, respectively). However, the overall impact on global productivity is low (∼ 3 %) since a large part of marine productivity is driven by nutrients recycled in the upper ocean layer or other local factors. Prominent changes are, nevertheless, found for regional productivity. Reductions of up to 20 % occur in oligotrophic regions such as the subtropical gyres in the Northern Hemisphere under pre-industrial conditions. In the subpolar Pacific, reduced pre-industrial Fe fluxes lead to a substantial decline of siliceous diatom production and subsequent accumulation of Si, P, and N, in the subpolar gyre. Transport of these nutrient-enriched waters leads to strongly elevated production of calcareous nanophytoplankton further south and southeast, where iron no longer limits productivity. The North Pacific is found to be the most sensitive to variations in depositional fluxes, mainly because the water exchange with nutrient-rich polar waters is hampered by land bridges. By contrast, large amounts of unutilized nutrients are advected equatorward in the Southern Ocean and North Atlantic, making these regions less sensitive to external nutrient inputs. Despite the lower aerosol N : P ratios with respect to the Redfield ratio during the pre-industrial period, the nitrogen fixation decreased in the subtropical gyres mainly due to diminished iron supply. Future changes in air pollutants under the Representative Concentration Pathway 8.5 (RCP8.5) emission scenario result in a modest decrease of the atmospheric nutrients inputs into the global ocean compared to the present day (∼ 13 %, ∼ 14 %, and ∼ 20 % for N, Fe, and P, respectively), without significantly affecting the projected primary production in the model. Sensitivity simulations further show that the impact of atmospheric organic nutrients on the global oceanic productivity has turned out roughly as high as the present-day productivity increase since the pre-industrial era when only the inorganic nutrients' supply is considered in the model. On the other hand, variations in atmospheric phosphorus supply have almost no effect on the calculated oceanic productivity.

An explicit estimate of the atmospheric nutrient impact on global oceanic productivity

State-of-the-art global nutrient deposition fields are here coupled to the biogeochemistry model PISCES to investigate the effect on ocean biogeochemistry in the context of atmospheric forcings for preindustrial, present, and future periods. Present-day atmospheric deposition fluxes of inorganic N, Fe, and P over the global ocean are accounted equal to ~40 Tg-N yr−1, ~0.28 Tg-Fe yr−1 and ~0.10 Tg-P yr−1. The resulting globally integrated primary production of roughly 47 Pg-C yr−1 is well within the range of satellite-based estimates and other modeling predictions. Preindustrial atmospheric nutrient deposition fluxes are lower compared to present-day (~51 %, ~36 %, and ~40 % for N, Fe, and P, respectively), resulting here in a lower marine primary production by ~3 % globally. Future changes in air pollutants under the RCP8.5 scenario result in a modest decrease of the bioaccessible nutrients input into the global ocean compared to present-day (~13 %, ~14 % and ~20 % for N, Fe and P, respectively), without significantly affecting the projected primary production in the model. The global mean nitrogen-fixation rates changed only marginally from preindustrial to future conditions (111 ± 0.6 Tg-N yr−1). With regard to the atmospheric inputs to the ocean, sensitivity model simulations indicate that the contribution of nutrients' organic fraction results in an increase in primary production by about 2.4 %. This estimate is almost equal to the effect of emissions and atmospheric processing on the oceanic biogeochemistry since preindustrial times in the model when only the inorganic fraction of the nutrients is considered. Although the impact of the atmospheric organic nutrients may imply a relatively weak response of marine productivity on a global scale, stronger regional effects up to ~20 % are calculated in the oligotrophic subtropical gyres. Overall, this work provides a first explicit assessment of the contribution of the organic forms of atmospheric nutrients, highlighting the importance of their representation in biogeochemistry models and thus the oceanic productivity estimates.

A Model interface for ERA5

<p>The ERA5 dataset provides a comprehensive view on recent climate data by assimilating vast amounts of historical observations into the ECMWF integrated forecast system, and as such establishing a reference point in the field of weather and climate modelling. The successor of ERA-interim is ubiquitous in the earth sciences, with applications such as boundary conditions for regional simulations, atmospheric forcings to ocean or land surface models, initial conditions to climate prediction experiments, etc.. The conventional workflow for such applications is to download the data, extract the necessary variables, optionally regrid or resample and save it in a model specific format. This procedure is time consuming, difficult to document properly and generates a lot of intermediate data of low reuse value. Here, we provide an alternative to this by wrapping access to the ERA5 dataset in a standardized OMUSE model interface. OMUSE is a Python framework for Earth System modelling, developed to simplify the use of simulation codes and enable new model couplings. Within OMUSE the ERA5 dataset is transparently accessed using the CDSAPI and the resulting interface is very much like an OMUSE interface for a simulation code. Data is pulled from the online climate data store only when needed and cached for later reuse. This approach simplifies the access and coupling of the ERA5 dataset with OMUSE model components and makes it trivially easy to repeat a model run with a different dataset or even replace it with a life model.</p>