Western boundary circulation driven by an alongshore wind: With application to the Somali Current system

The linear, continuously stratified, eastern-boundary model of McCreary (1981) is extended to apply to a western ocean boundary and to wind fields with curl. The model has vertical and horizontal mixing, and both types of mixing are important in its dynamics. Solutions are represented as expansions in vertical modes, and the dynamics of low-order and high-order modes are very different. Low-order modes tend to be in Sverdrup balance in the interior ocean, and to form a Munk layer at the coast. High-order modes are in Ekman balance in the interior ocean, and the coastal balance is two dimensional.The model is forced by steady northward winds, both with and without curl. Solutions at the western boundary differ fundamentally from comparable ones at the eastern boundary. For winds without curl, the surface jet is stronger, and there is essentially no coastal undercurrent. This difference is due to the fact that at an eastern boundary the currents associated with low-order modes leak offshore. For winds with curl, a sizeable undercurrent develops, but only south of the region of the wind. A strong onshore current, located near the southern edge of the wind, is generated by offshore wind curl. Part of this current turns southward at the coast, thereby generating the undercurrent in the south.The existence of this undercurrent is in accord with observations off Somalia, where a southward undercurrent has been observed at 5N during the Southwest Monsoon. The wind at this time is oriented alongshore, reaches maximum strength well to the north of 5N, and is associated with a region of large, negative wind curl off the coast

A numerical investigation of the Somali Current during the Southwest Monsoon

The dynamics of the Somali Current system during the Southwest Monsoon are investigated using a 2½-layer numerical model that includes entrainment of cool water into the upper layer. Entrainment cools the upper layer, provides interfacial drag, and prevents the interface from surfacing in regions of strong coastal upwelling. Solutions are forced by a variety of wind stress fields in ocean basins with western boundaries oriented either meridionally or at a 45° angle. Solutions forced by southern hemisphere easterlies develop a strong coastal current south of the equator. When the western boundary is slanted, this current bends offshore at the equator and meanders back into the ocean interior. No cold wedge forms on the Somali Coast. These solutions suggest that the southern hemisphere trades are not an important forcing mechanism of the Somali Current circulation. Solutions forced by northward alongshore winds differ considerably depending on the orientation of the western boundary and the horizontal structure of the wind. When the boundary is meridional and the wind is uniform (a curl-free wind field), solutions continuously shed eddies which propagate northward along the coast and weaken. When the boundary is meridional and the wind weakens offshore, they reach a completely steady, eddy-free state with no coastal upwelling. If the boundary is slanted and the wind does not vary alongshore, solutions reach a steady state that now contains stationary gyres and cold wedges. If the boundary is slanted and the forcing is a strong wind patch confined north of the equator, the flow field slowly vacillates between single-gyre and double-gyre states. Solutions are also forced by an idealized representation of the observed alongshore wind field, consisting of two components: a moderate background field (∼1 dyn/cm2) turned on in May, and a Findlater jet (∼4 dyn/cm2) turned on gradually in June. A single gyre, the Southern Gyre, initially develops south of 4N due to the background wind, and a second gyre, the Great Whirl, develops later between 4N–9N in response to the Findlater jet. Cold wedges form on the northern flanks of both gyres. In some of the solutions, the Southern Gyre moves northward and coalesces with the Great Whirl in early September, before the monsoon begins to weaken. Thus the collapse of the two-gyre system is part of the adjustment of the model to the peak phase of the Southwest Monsoon, and is not due to a relaxation of the wind

Thermohaline forcing of eastern boundary currents: with application to the circulation off the west coast of Australia

The linear, viscid, continuously stratified model of McCreary (1981) is extended to allow for thermohaline forcing by a specified, longitudinally independent, surface density field ρs. When the ocean is unbounded and ρs is steady, the density field is altered throughout the water column by vertical diffusion. If ρs increases poleward, the resulting pressure field slopes downward toward the pole in the upper water column, and there is an associated eastward geostrophic current. This interior current forces downwelling at an eastern ocean boundary, and generates a poleward surface coastal current and an equatorward undercurrent. For realistic choices of model parameters the coastal circulation is as strong as, and opposite in direction to, that caused by a typical equatorward wind stress τy. When ρs oscillates at the annual cycle, the unbounded flowis confined to a surface boundary layer. The coastal circulation is qualitatively quasi-steady, but also has characteristics of a vertically propagating Kelvin wave. One solution is forced by an idealized representation of the observed ρs and τy fields off the west coast of Australia. This solution compares well with observations of the oceanic circulation there. In particular, there is a surface coastal jet (the model Leeuwin Current) that flows against the wind. This successful comparison suggests that the mean circulation in the region is significantly forced by ρs, whereas the annual variability is strongly forced by τy

On the dynamics of the California Current system

The dynamics of the California Current system are studied using two ocean models, one with a shelf and one without. Both models are viscid and linearized about a background density field Pb(Z), Solutions are forced by steady and annually periodic winds with and without curl, and by an idealization of the observed wind field off California. Solutions forced by a steady, equatorward, curl-free wind τy all have an equatorward surface coastal jet and a poleward undercurrent. Due to the β-effect and horizontal mixing, the circulation is not necessarily confined within a Rossby radius of the coast. The strength and structure of the currents vary considerably with parameters, the currents being stronger and broader when the forcing includes remote winds to the south and when ρb has a near-surface pycnocline. If τy oscillates at the annual cycle the response is qualitatively quasi-steady, but it also involves a poleward, offshore and vertical propagation of waves, and the maximum coastal current leads τy by several weeks.Solutions forced by a steady, positive wind curl τyx develop a deep, broad, poleward surface current near the coast, consistent with Sverdrup theory. Interestingly, there is also an equatorward surface flow located farther offshore, which exists because of the vertical mixing in the model. Solutions are not very dependent on model parameters, because they are primarily interior currents directly in balance with the wind curl and do not require the coast for their existence. If τyx oscillates at the annual cycle, the response is not at all quasi-steady, and the maximum coastal current lags τyx by 1–2 months. Solutions forced by an idealization of the observed wind field off California compare favorably with observations, but only if Pb has a realistic pycnocline and the forcing includes remote winds off Baja California. Forcing by positive τyx accounts for both the poleward Davidson Current during the winter and the equatorward flow located more than 100 km offshore throughout the year. The coastal jet forced by τy provides summertime equatorward flow within 100 km of the coast that is strong enough to reverse the poleward flow driven by τyx

CHEMICAL INVESTIGATION OF NEEM LEAF GLYCOPROTEIN USED AS IMMUNOPROPHYLACTIC AGENT FOR TUMOR GROWTH RESTRICTION

Objective: Unique immune modulatory function of an aqueous preparation of neem leaf (NLP) in relation to cancer has already been reported. The objective of this present study is to find out the active component present in NLP.Methods: NLP was exposed to a gradient of temperature, pH and enzymes to use for mice immunization before tumor inoculation. Glycoprotein extracted from NLP was purified and analyzed by using Folin's phenol reagent, polyacrylamide gel electrophoresis, scanning electron microscopy and amino acid analysis. Carbohydrate moiety of this protein was analysed by GLC-MS. Immunogenicity was checked by ELISA and immunoblotting.Results: Exposure of NLP to adverse temperature and pH causes significant reduction in tumor growth restricting function of NLP. Treatment of NLP with proteolytic enzymes results abolition of the tumor growth restriction in mice. Biochemical assays indicated the presence of a glycoprotein in NLP, designated as neem leaf glycoprotein (NLGP) which appeared in non-denatured PAGE as a single band, and as three bands in SDS-PAGE having molecular weights 48 Kda, 24 Kda and 15 Kda. NLGP constitutes the carbohydrate moiety of about 33% consisting of arabinose, galactose and glucose. This glycoprotein consisted of seventeen amino acids of which nine were essential. Immunogenecity of this protein was defined by strong reaction of the ant-NLGP sera with NLGP by ELISA and immunoblot.Conclusion: Overall results demonstrated the immense potential of newly identified NLGP, present in NLP as an immunoprophylactic agent for tumor growth restriction.Â

Interaction of internal waves and mean flow observed near a coast

Vortex stretching has been proposed as a possible mechanism by which internal waves can extract energy from the mean flow. Relationships between the slowly varying (ω \u3c 0.25 cpd) and rapidly varying (0.13 cph \u3c ω \u3c 0.5 cph) components of the flow have been examined in a 4-month-long data set taken off the coast of British Columbia. The rapidly varying component of horizontal velocity generally rotates clockwise, and is in rough agreement with internal wave dynamics. It is horizontally incoherent within a distance of 10 km and is vertically coherent across the water column with a nearly 180° phase change. Scatter plots show that the wavefield is anisotropic, with the Reynolds stresses generally obeying uv \u3c 0, vw \u3c 0 and uw \u3e 0, where (u, v, w) are the fluctuating velocity components in the (onshore, alongshore, upward) directions. Instances have been found in which time variations of uv and the mean horizontal shear rate Vx are negatively correlated, with an implied horizontal viscosity of VH ∼ (3 ± 2) × 105 cm2/s. No correlation of vw and the mean vertical shear Vz is found. It is suggested that nonlocal behavior is important because propagation times in the vertical are smaller than the interaction times of the wave packets. With the observed shear rates and the wave energy levels, the vertical viscosity is unlikely to be beyond the range ± 20 cm2/s

Clinico-mycological study of dermatophytosis in a tertiary care centre in North Eastern India

Background: The dermatophytosis constitutes a group of superficial fungal infections of keratinized tissues, namely, the epidermis, hair, and nails. The present study was undertaken to find out the clinical profile of dermatophytosis and to identify the causative fungal species in the various clinical presentations. Materials & Methods: This was a hospital‐based observational study. One hundred clinically suspected patients attending OPD of M. G. M. Medical College and Lion Seva Kendra Hospital were included in the study. History was taken, general physical and cutaneous examination was done and details of skin lesions noted. Direct microscopy in 10% KOH (40% KOH for nail) and fungal culture on SDA with 0.05% chloramphenicol and 0.5% cycloheximide was done in every case. Chi‐square test and contingency coefficient test were used as significant tests for analysis. Results: In the present study, tinea accounted for 22.68 % of the total Dermatology OPD cases of which male constituted 59 % and 41 % females. The mean age was 38.4 ± 16.98 years. Majority were of age group 21-30 years followed by age group 31-40 years.Out of all the samples 68 cases were KOH positive as compared to 61 cases which were culture positive. Two KOH negative cases were culture positive and 9 culture negative cases came out to be KOH positive. Out of 81 skin scrapping samples 54 were KOH positive and 47 were culture positive, 11 nail clipping samples 8 were KOH as well as culture positive and out of 8 hair pluck samples 6 were KOH as well as culture positive.In 61 culture positive cases there were 7 non-dermatophytic growth which included 4 aspergillus spp. and 3 candida spp. Conclusion: Dermatophytosis is one of the most common if not the commonest dermatological condition we come across the Dermatology OPD. It most commonly affects the young age group rather than extremes of age

Fluid Mechanics

xxvi, 891hlm; 21c