Zonal surface wind jets across the Red Sea due to mountain gap forcing along both sides of the Red Sea

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 36 (2009): L19605, doi:10.1029/2009GL040008.Mesoscale atmospheric modeling over the Red Sea, validated by in-situ meteorological buoy data, identifies two types of coastal mountain gap wind jets that frequently blow across the longitudinal axis of the Red Sea: (1) an eastward-blowing summer daily wind jet originating from the Tokar Gap on the Sudanese Red Sea coast, and (2) wintertime westward-blowing wind-jet bands along the northwestern Saudi Arabian coast, which occur every 10–20 days and can last for several days when occurring. Both wind jets can attain wind speeds over 15 m s−1 and contribute significantly to monthly mean surface wind stress, especially in the cross-axis components, which could be of importance to ocean eddy formation in the Red Sea. The wintertime wind jets can cause significant evaporation and ocean heat loss along the northeastern Red Sea coast and may potentially drive deep convection in that region. An initial characterization of these wind jets is presented.Supported by Award Numbers USA 00001, USA 00002, and KSA 00011 made by KAUST

Reconciling down core anticorrelation of diatom carbon and nitrogen isotopic ratios from the Southern Ocean

[1] Oceanic nutrient cycling in the Southern Ocean is supposed to have an important impact on glacial-interglacial atmospheric CO(2) changes and global climate. In order to characterize such nutrient cycling over the last two climatic cycles we investigated carbon and nitrogen isotopic ratios of diatom-bound organic matter (delta(13)C(diat) and delta(15)N(diat)- respectively) in two cores retrieved form the Atlantic and Indian sectors of the Antarctic Ocean. The two cores show the same isotopic patterns. The delta(13)C(diat) values are depleted during glacial periods and enriched during interglacial periods, indicating lower productivity during cold times. The delta(15)N(diat) values are enriched during glacial periods and depleted during interglacial periods, arguing for greater nitrate utilization during cold times. Taken at face value, this apparent contradiction leads to opposite conclusions on the role of the Southern Ocean biological pump on the atmospheric CO, changes. However, the two sets of data can be reconciled by a "sea ice plus mixing rate scenario" that calls upon a balance between the effect Of Cutting off gas transfer at the ocean-atmosphere boundary and the effect of reducing vertical transport of nutrients through the pycnocline

A radiolarian-based transfer function for the estimation of sea-surface temperatures in the Southern Ocean (Atlantic Sector)

A new radiolarian-based transfer function for sea surface temperature (SST) estimations has been developed from 23 taxa and taxa groups in 53 surface sediment samples recovered between 35° and 72°S in the Atlantic sector of the Southern Ocean. For the selection of taxa and taxa groups ecological information from water column studies was considered. The transfer function allows the estimation of austral summer SST (December-March) ranging between -1 and 18°C with a standard error of estimate of 1.2°C. SST estimates from selected late Pleistocene squences were sucessfully compared with independend paleotemperature estimates derived from a diatom transfer function. This shows that radiolarians provide an excellent tool for paleotemperature reconstructions in Pleistocene sediments of the Southern Ocean

Assessment of the reliability of wave observations from Voluntary Observing Ships: insights from the validation of a global wind wave climatology based on Voluntary Observing Ship data

This paper describes development and validation of a global climatology of basic wave parameters based on the voluntary observing ship (VOS) data from the Comprehensive Ocean-Atmosphere Data Set collection. Climatology covers the period 1958–1997 and presents heights and periods for the wind sea, swell, and significant wave height (SWH) over the global ocean on 2° × 2° spatial resolution. Significant wave height has been derived from separate sea and swell estimates by taking square root of the sum of squares for the seas and swells propagating approximately in the same direction and assuming SWH to be equal to the higher of the two components in all other cases. Special algorithms of corrections were applied to minimize some biases, inherent in visual wave data. Particularly, we corrected overestimation of small seas, corrected underestimation of periods, and analyzed separation between sea and swell. Validation included estimation of random observational errors, observation of sampling errors, and comparison with the alternative wave data. Estimates of random observational errors show that for the majority of locations, observational uncertainties are within 20% of mean values, which allows us to discuss quantitatively the produced climatology. Biases associated with inadequate sampling were quantified using the data from high-resolution WAM hindcast for the period 1979–1993. The highest sampling biases are observed in the South Ocean, where wave height may be underestimated by 1–1.5 m because of poor sampling, primarily associated with a fair weather bias of ship routing and observation. Comparison to the other VOS-based products shows in general higher SWH in our climatology, especially in the midlatitudes. However, comparison with the altimeter data shows that even for well-sampled regions, high waves are still underestimated in VOS, suggesting a ubiquitous fair weather bias. Further ways of improving VOS-based wave climatologies and possible applications are discussed