An Investigation of Large Cross-Track Errors in North Atlantic Tropical Cyclones in the GEFS and ECMWF Ensembles

The largest medium-range (72-120 h) cross-track errors (CTE) of tropical cyclone (TC) forecasts from the Global Ensemble Forecast System (GEFS) over the northern Atlantic Ocean are examined for the 2008-2016 seasons. The 38 unique forecasts within the upper-quartile most negative CTEs (i.e., left-of-track bias larger than 250 km by 72 h) do not have a clear common source of steering error, though 12 of the forecasts involve the underprediction of a weak upper-level trough to the west of the TC by 36 h. Meanwhile, at least 18 of the 36 most positive CTEs (right-of-track bias) are associated with TCs embedded in the southwest extent of a subtropical ridge, the strength of which is increasingly underpredicted during the first 24 h of the forecast. Excessive height falls north of the TC are driven by overpredicted divergence aloft, which corresponds to overpredicted TC outer-core convection. The convection is triggered by a 5-to-20% overprediction of near-TC moisture and instability in the initial conditions. Weather Research Forecast (WRF) simulations are run at 36-, 12-, and 4-km grid spacing for select right-of-track cases, using the GEFS for initial and lateral boundary conditions. The 36-km WRF reproduces the same growth of errors as the GEFS due to in part sharing the same stability and moisture errors in the initial conditions. Changes in the convective parameterization affect how quickly these errors grow by affecting how much convection spins-up. The addition of a 4-km nest with no convective parameterization causes the errors to grow ~20% faster, resulting in an even larger right-of-track error.

Development of a New Ship Adaptive Weather Routing Model Based on Seakeeping Analysis and Optimization

This paper provides a new adaptive weather routing model, based on the Dijkstra shortest path algorithm, aiming to select the optimal route that maximizes the ship performances in a seaway. The model is based on a set of ship motion-limiting criteria and on the weather forecast maps, providing the sea state conditions the ship is expected to encounter along the scheduled route. The new adaptive weather routing model is applied to optimize the scheduled route in the Northern Atlantic Ocean of the S175 containership, assumed as a reference vessel, based on the weather forecast data provided by the Global WAve Model (GWAM). In the analysis, both wave and combined wind/swell wave conditions are embodied to investigate the incidence on the optimum route assessment. Furthermore, the effect of the vessel speed on the optimum route detection is also investigated. Current results clearly show that it is possible to achieve appreciable improvements, up to 50% of the ship seakeeping performances, without excessively increasing the route length and the voyage duration.

Probing the use of coccolith geochemistry as a proxy for past carbon dioxide concentrations - Insights from Termination II in the Northern Atlantic Ocean

<p>Despite their omnipresence in pelagic carbonate sediments, the coccoliths, the calcite biominerals produced by the coccolithophores, have historically been under-exploited in palaeoenvironmental studies. This is due, in part, to their small size (2-20 microns), which makes them difficult to isolate from other particles, and to the large differences in isotopic composition existing between coccolith calcite and equilibrium conditions. This so-called “vital effect” complicates the use of coccolith geochemistry to derive paleoclimatic signals with confidence. Recent studies from cultured and fossil coccoliths have shown that the oxygen and carbon isotopic compositions of the coccoliths are particularly sensitive to the availability of CO<sub>2</sub> in the environment, upon which the coccolithophores rely for their photosynthetic activity. Therefore, our approach here is to test whether the coccolith geochemistry can be used as a novel proxy for surface ocean and atmospheric CO<sub>2</sub> concentrations.</p><p>In this study, different size fractions of coccoliths were extracted from carbonate sediments of site MD95-2037 in the Northern Atlantic Ocean and run for isotopic analysis. Using calibrations between coccolith vital effects and seawater [CO<sub>2</sub>] from culture studies, we present a seawater [CO<sub>2</sub>] curve for site MD95-2037 across Termination II (130 kyrs). The curve was in turn translated into atmospheric <em>p</em>CO<sub>2</sub> estimates taking into account changes in ancillary parameters (such as temperature). Coccolith-derived CO<sub>2</sub> concentrations yield comparable values, both for the absolute numbers and trends, to the record from Vostok ice cores. This coherency is confirmed by a 80 ppm-shift in <em>p</em>CO<sub>2</sub> concentrations in the North Atlantic between glacial and interglacial times reconstructed from the coccolith record.</p><p>Altogether, these datasets confirms that coccolith geochemistry can indeed be used to reconstruct past changes in [CO<sub>2</sub>]<sub>sw</sub>. Perspectives for this study include providing the scientific community with a new record of <em>p</em>CO<sub>2</sub> for periods extending beyond the Vostok record, in particular the Mid-Pleistocene Transition, where a decrease in global <em>p</em>CO<sub>2</sub> has been put forward to explain the shift from 41 kyr- to 100 kyr-cycles in glacial-interglacial cycles.</p>

Amphi-Pacific tropical disjunctions in the bryophyte floras of Asia and the New World

Disjunctions between tropical America and tropical Asia, commonly called amphi-Pacific tropical disjunctions, have frequently been discussed among flowering plants but have received very little attention in bryology. A screening of the literature revealed nine species and sixteen genera or infrageneric taxa of bryophytes with amphi-Pacific tropical (or subtropical) ranges. They include Austinia tenuinervis, Diphyscium chiapense, D. longiflorum, Elmerobryum, Fissidens sect. Sarawakia, Ganguleea angulosa, Hydrogonium arcuatum, Hymenostyliella, Hymenostylium aurantiacum, Luisierella barbula, Mniomalia, Rozea, Sphaerotheciella and Sorapilla among the mosses and Ceratolejeunea grandiloba, Drepanolejeunea subg. Rhaphidolejeunea, Lejeunea sect. Echinocolea, Lobatiriccardia, Myriocoleopsis sect. Myriocoleopsis, Phycolepidozia, Pictolejeunea, Rectolejeunea, Southbya organensis and Vitalianthus among liverworts. All of them occur in tropical or subtropical Asia and the Neotropics but are not known from Africa. The causes of the amphi-Pacific tropical disjunctions in bryophytes are still unclear. In flowering plants, molecular analyses indicate that amphi-Pacific tropical ranges frequently resulted from past migration across Eurasia and the northern Atlantic Ocean, followed by local extinction. This scenario may also have operated in amphi-Pacific bryophytes but some might have reached South America via the southern Pacific migration route. The possibility of direct long-range dispersal across the Pacific Ocean cannot be ruled out and this scenario seems likely for Southbya organensis, which occurs on Hawaii and freely produces spores and small gemmae. The possibility that the disjunctive ranges reflect insufficient collecting and that some taxa also occur in Africa should also be taken into account. There is no strong evidence for human introduction of amphi-Pacific tropical bryophytes. The new combinations Lejeunea sect. Echinocolea (R.M.Schust.) Gradst. comb. nov. and Myriocoleopsis sect. Protocolea (R.M.Schust.) Gradst. comb. nov. are proposed.