Wind Density Profile Research Articles

Wind-triggered events of phytoplankton downward flux in the Northeast Water Polynya

Phytoplankton carbon fluxes were studied in the Northeast Water (NEW) Polynya, off the eastern coast of Greenland (79° to 81°N, 6° to 17°W), during summer 1993. The downward flux of organic particles was determined during 54 days using a sediment trap moored at a fixed location, below the pycnocline (130 m). The hypothesis of the present study is that wind events were ultimately responsible for the events of diatoms downward flux recorded in the trap. Wind conditions can influence the vertical transport of phytoplankton by affecting (1) the environmental conditions (e.g. hydrostatic pressure, nutrient concentrations, and irradiance) encountered by phytoplankton during their vertical excursion, and (2) the aggregation and disaggregation of phytoplankton flocs. The first mechanism affects the physiological regulation of buoyancy, whereas the second one affects the size and shape of settling particles. Using field data (wind velocity, density profiles and phytoplankton abundance), we assessed the potential aggregation and the vertical excursion of phytoplankton in surface waters. The results show that, upstream from the trap, wind and hydrodynamic conditions were sometimes favourable to the downward export of phytoplankton. Lag-correlation between time series of wind and phytoplankton downward flux shows that flux events lagged wind events by ca. 16 days. Given that the average current velocity in the top 100 m was ca. 10 cm s −1, a lag of 16 days corresponded to a lateral transport of ca. 130 km, upstream from the sediment trap, where phytoplankton production was lower than at the location of the trap. According to that scenario, 21% to 60% of primary production was exported to depth during wind events. If we had assumed instead a tight spatial coupling between the material collected in the trap and the relatively high phytoplankton production at the location of the trap, we would have concluded that <7% of primary production was exported to depth. The difference between the two scenarios has great implications for the fate of phytoplankton. Our results stress the importance of investigating the spatial coupling between surface and trap data before assessing the pathways of phytoplankton carbon cycling.

An estimate of large‐scale solar wind density and velocity profiles in a coronal hole and the coronal streamer belt

With the use of the total electron content data obtained by the Ulysses Solar Corona Experiment (SCE) during the first solar conjunction in summer 1991, two data sets were selected, one associated with a coronal hole and the other associated with coronal streamer belt crossings. To determine a large‐scale coronal streamer belt density profile, the electron content of the tracking passes embedded in the coronal streamer belt were corrected for the contributions from coronal hole densities. The inferred large‐scale streamer belt electron density profile has a radial falloff exponent of −2.4 for distances greater than 7 Rs implying the acceleration of the slow solar wind according to υ(r) ∼ r0.4, in qualitative agreement with SOHO results. The acceleration terminates beyond 60 Rs in agreement with Helios in situ observations. All radial electron density profiles inferred from coronal radio sounding observations, particularly during times of high solar activity, are dominated by coronal streamer contributions. They are applicable to coronal streamers, confined to a limited latitude range about the heliospheric current sheet, and they are not representative of a large‐scale mean coronal electron density profile. Because of a lack of data, similar analysis of the coronal hole electron content data was not unequivocally feasible. The coronal hole tracking passes corrected for contributions from coronal streamer areas display large electron content and density fluctuations inconsisting with the plume interpretation by Woo [1996]. Assuming that the lowest densities represent typical hole densities and comparing these with streamer densities at the same distance, we found the streamer‐to‐hole density ratio to be a factor of 10, which agrees with white light coronagraph results.

The interaction of southwest monsoon upwelling, advection and primary production in the northwest Arabian Sea

A biological model comprising phytoplankton, Zooplankton, detritus, and nitrogen pools has been coupled to a 3-layer reduced-gravity ocean circulation model of the Arabian Sea through the vertical mixing and horizontal transport fields. Coupled biophysical interactions during the southwest monsoon have been investigated using experiments with progressively more physical forcing: (1) initial-value biological calculations with no forcing; (2) upwelling simulations for the southwest monsoon that incorporate vertical forcing only; and (3) coupled physical-biological model experiments that use both upwelling and horizontal advection, and are forced by monthly varying climatological wind stresses and density profiles for the Arabian Sea. The initial-value and upwelling experiments indicate the roles of grazing pressure and remineralization of detritus when physical forcing is present. The coupled model experiments demonstrate the importance of coastal upwelling and offshore advection in determining patterns of total nitrogen in surface waters, both near the coast and offshore. Offshore jets are significant as sources of both transported nutrients and biomass in open waters far from coastal upwelling areas.

Warm O+ polar wind and the De‐1 polar cap electron density profile

Theoretical steady state semikinetic polar wind density profiles, based on DE1/RIMS polar wind data [Chandler et al., 1991] at low altitudes (up to 3700 km), were obtained which agree very well with the power law (ne = 490 r−3.85 cm−3) electron density profile measured by the DE1/PWI for high altitudes [Persoon et al., 1983] (2–5RE). The polar wind is found to be O+ dominated for the full altitude range considered (up to 8 RE). Multiple solutions are obtained for various combinations of base altitude ion temperatures and electron temperatures, such that the densities fit the Persoon et al. profile. For example, good fits to measured density profile are found for low base ion temperatures (5000 K) and high electron temperatures (9000 K), and also for unheated H+ and O+ (3000 K) with electron temperatures of 11,000 K. Below 2.8 RE the theoretical polar wind density deviates somewhat from the r−3.85 power law. It is concluded that this theoretical polar wind density profile, with a sum of base electron and ion temperatures of 14,000 K, yields a close match with the measured DE‐1 electron density profile.

Recent work on mid-latitude and equatorial sporadic- E

Theoretical and experimental work since 1970 is summarized. Mid-latitude sporadic- E is most likely due to a vertical shear in the horizontal east-west wind and this theory accounts for the detailed observations of the wind and electron density profiles. Preferred heights of sporadic- E are separated by about 6km and descending layers are often seen moving down with velocities in the range 0.6–4 ms −. Sometimes sporadic- E layers are very flat and uniform, and at other times form clouds of electrons 2–100km in size moving horizontally at 20–130 ms −1. Sporadic- E is probably not correlated with meteor showers; this is a rather surprising result since the ions are meteor debris. The major problems with windshear theory are to account for the dramatic seasonal variation and, to a lesser extent, for the geographical and diurnal distributions. The Q-type equatorial sporadic- E appears to be due to the gradient instability. There is a very much smaller amount of new experimental data available in this area.

A two‐fluid solar wind model with Alfven waves: Parameter study and application to observations

The effects of Alfven waves from the inner corona on the solar wind density profile, flow velocity and on the random motion of protons are studied. Different base densities, temperatures, and wave velocity amplitudes, as well as different flow geometries, are considered. The model calculations are compared to simultaneous observations of the electron density profile and the resonantly scattered Lyman alpha line. Present observations, out to 4 solar radii, can be used to place limits on the coronal base density and temperature, and put an upper limit on the wave amplitude. It is pointed out that future observations of the electron density and the Lyman alpha line, out to larger heliocentric distances, and of lines from heavier elements, should be used to place more stringent constraints on the amplitudes of MHD waves in the corona.