Downwelling Of Surface Water Research Articles

Cold Sea Surface Temperature near Cheju Island Responding to Strong Cyclonic Wind and Positive Geopotential Tendency behind a Typhoon Center along its Track

The response of sea surface temperature (SST) before and after the passage of Typhoon-18 Songda in the vicinity of Chjeu Island in the southern sea of Korea was investigated using satellite-derived GOES-MCSST (SST), GOES infrared cloud image and a three dimensional WRF-3.0 model with FNL initial meteorological data on September 5 to 8, 2004. On September 4, before the typhoon passed by Cheju Island, the SST extending southwards and eastwards of the island was 27°C. However, after the typhoon passed by the island at 2100 LST, September 7, the SST decreased by 2°C to 25°C. Asymmetrical-cyclonic surface wind generated by the combination of the movement of the typhoon and the cyclonic winds of the typhoon itself, caused divergence of wind driven currents, which induced upwelling of deep sea colder water to the sea surface and outward spreading of cold waters near the island. This resulted in the decrease of SST and a negative maximum geopotential tendency of 500 hPa for 24 hours (∂Φ/∂t; m/day) was detected in the center of the typhoon eye, where the thinner atmospheric layer existed. This induced a decrease in the sea surface height and in the downwelling of surface waters. A positive maximum geopotential tendency was detected behind the typhoon center along its track, where maximum expansion of the atmospheric depth caused the level of the sea surface to rise and upwelling of deep sea cold waters to the surface. Thus, the slope height ranging from 422 to 639 m/day between two maxima of geopotential tendencies could strongly influence the sea surface elevation, thereby inducing a very strong upwelling and outward spreading of deep sea colder waters toward the inclined sea surface, resulting in a decrease of SST in the wake of the typhoon track.

Role of localized mixing around the Kuril Straits in the Pacific thermohaline circulation

We investigate the Pacific thermohaline circulation induced by the locally enhanced vertical mixing around the Kuril Straits by using a general circulation model. When the strong vertical mixing reaches the sea surface, localized upwelling is induced from the depth to the surface. On the contrary, in the cases where the strong vertical mixing does not reach the sea surface, downwelling of surface water is induced in the shallow layer while upwelling of deep water is induced below. The structure of the meridional overturning circulation in the Pacific Ocean significantly differs depending on whether the surface buoyancy flux is large enough to sustain upwelling of deep water or not. The mixing‐induced downwelling of shallow water is not associated with the sea surface cooling, and the source of dense water is in the deep ocean. Among the non‐surface‐reaching mixing cases, the depth that separates the downwelling and upwelling is found to be relatively insensitive to the depth where the vertical diffusivity sharply changes.

Nutrient retention within the hyporheic zone of a low order sandstone stream (Weidlingbach, Lower Austria)

In this study at the Weidlingbach, a fourth order sandstone stream, the hydrological exchange between surface and interstitial water as well as the retention potential of the hyporheic zone for inorganic nutrients were studied. For this purpose, we performed shortterm nutrient additions (ammonium, nitrate, phosphate) at a 75 m long, third order study reach between May and August 2004. Additionally, hydrological and chemical parameters to estimate water exchange (VHG, hydraulic conductivity, conductivity, oxygen concentration) were measured in the stream and interstitial water. Sediments at the study reach could be divided into sites with either upwelling or restricted water exchange (low permeability, positive VHGs, low oxygen content) and sites which were characterized by a significant downwelling of surface water. Hyporheic nutrient uptake was measured at these latter sites. The nutrient with the highest retention efficiency was ammonium, followed by phosphate and nitrate. Vertical uptake curves indicated that the retention efficiency was highest in the sediments at the surface. These results imply that, at the Weidlingbach, the hyporheic zone does not considerably contribute to stream retention and that the surface sediments and the surface water play a greater role in nutrient cycling.

Le Gulf Stream et le climat

Dédiée aux sciences de l'atmosphère, au climat et à d'autres domaines connexes, tels que l'océanographie ou la glaciologie, La Météorologie, révisée par des pairs et publiée en français, s'adresse aux professionnels de la météo et du climat, aux enseignants, aux étudiants, aux amateurs et aux utilisateurs. La Météorologie a succédé en 1925 à l'Annuaire de la Société météorologique de France (1852-1924) qui avait lui-même succédé à l'Annuaire météorologique de la France (1849-1851).

Thermal heterogeneity in the hyporheic zone of a glacial floodplain

We examined the thermal regime of surface and hyporheic waters at three kryal sites and four krenal streams within the channel network of a glacial floodplain. Temperature was continuously measured for 1 year in the surface stream and at sediment depths of 30 and 80 cm. The vertical pattern of water temperature was strongly influenced by the direction and intensity of surface water – groundwater exchanges. At sites characterized by strong downwelling of surface waters, the thermal regimes of surface and hyporheic waters were virtually identical. In contrast, inputs of groundwater substantially increased mean summer temperatures in the hyporheic zone of the main kryal channel, decreased summer temperatures in the hyporheic zone of krenal streams, and elevated hyporheic temperatures of all stream types during winter. Groundwater from different sources had dramatically different effects on the seasonal regime of temperature in the hyporheic zone. Inflow of shallow alluvial groundwater had minimal effects on ...

A calcite dissolution pulse in the Norwegian-Greenland Sea during the last deglaciation

Carbonate preservation profiles in the Atlantic Ocean and the Norwegian-Greenland Sea seem to be out-of phase during the last deglaciation. A possibly time transgressive deglacial preservation spike in the N-Atlantic overlaps with a major calcite dissolution pulse in the Norwegian Sea. Contemporaneously major changes in surface and bottom water circulation of the Norwegian-Greenland Sea occurred. Isotopic and sedimentological evidence suggests that bottom water formation in the Norwegian-Greenland Sea was almost shut down during the last maximum glaciation and probably also during the first part of the last deglaciation. During that time corrosive bottom waters might have filled the Norwegian Sea deep sea basins causing carbonate dissolution at the sea floor. Subsequently, the reinitiation of deep water formation could have been coupled with increased resuspension of organic matter and/or reworking of older organic matter rising the p CO2 of bottom waters and contributing to carbonate dissolution at the sea floor. Additionally, large volumes of atmospheric CO2 stored before the Younger Dryas might have been pumped into the deep sea possibly by downwelling of surface waters and been neutralized against carbonate at the sea floor.

Carbon Exchange Between Atmosphere and Oceans in a Latitude-Dependent Advection-Diffusion Model

Marine transport of inorganic and organic carbon is simulated by means of a computer model in which the oceans are divided into a high and low latitude region. Water transport (and with it carbon transport) is reproduced 1) as downwelling of surface waters at low latitudes, and 2) in general, as different depth-dependent turbulent diffusion in both deep-sea regions. The model is calibrated with pre-bomb 14C and validated against perturbations of total carbon, 13C/C- and 14C/C-ratios; it is compatible with carbon release from fossil fuels and from biogenic sources.