Mesoscale subduction at the Almeria-Oran front. Part 1: ageostrophic flow

This paper presents a detailed diagnostic analysis of hydrographic and current meter data from three, rapidly repeated, fine-scale surveys of the Almeria-Oran front. Instability of the frontal boundary, between surface waters of Atlantic and Mediterranean origin, is shown to provide a mechanism for significant heat transfer from the surface layers to the deep ocean in winter. The data were collected during the second observational phase of the EU funded OMEGA project on RRS Discovery cruise 224 during December 1996. High resolution hydrographic measurements using the towed undulating CTD vehicle, SeaSoar,. traced the subduction of Mediterranean Surface Water across the Almeria-Oran front. This subduction is shown to result from a significant baroclinic component to the instability of the frontal jet. The Q-vector formulation of the omega equation is combined with a scale analysis to quantitatively diagnose vertical transport resulting from mesoscale ageostrophic circulation. The analyses are presented and discussed in the presence of satellite and airborne remotely sensed data; which provide the basis for a thorough and novel approach to the determination of observational error

Ageostrophic frontal processes controlling phytoplankton production in the Catalano-Balearic Sea (Western Mediterranean)

Plankton production in marginal seas is characterized by significant mesoscale variability, as often inferred by satellite observations. The Catalano-Balearic Sea in the Western Mediterranean is one of such areas and is the focus of this coupled physicalbiological process study. We use a three dimensional biophysical model to understand how the mesoscale variability of the regional characteristics was controlled by quasigeostrophic (weakly nonlinear) and ageostrophic (moderately nonlinear) dynamics of the coastal boundary current and associated instabilities. Ageostrophic motion was most effective within the slope area where more pronounced meanders promoted enhanced upward pumping of subsurface nutrients into the euphotic zone and thus led to higher and broader coverage of phytoplankton biomass on anticyclonically-dominated onshore side of the front. On the contrary, the circulation further offshore, in the Balearic basin located further south, was controlled mainly by the quasi-geostrophic cyclonic eddies that were associated with a weak upward motion and thus unable to provide sufficiently high nutrient injections into the euphotic layer. However, these eddies played an effective role redistributing phytoplankton biomass that originated from the highly productive Iberian shelf and led to a patchy distribution over the basin, as seen in satellite imagery. In addition, the anticyclonic eddies developed in close proximities of the Balearic islands provided occasionally localized high phytoplankton patches in response to the agestrophic dynamics. It appears that the relatively low surface chlorophyll concentration shown by the satellite data does not necessarily imply poor phytoplankton production but may reflect an efficient energy flow towards higher trophic levels as supported by the zooplankton and fishery observations in the Catalano- Balearic Sea.JRC.H.1 - Water Resource

Fueling Plankton Production By a Meandering Frontal Jet: A Case Study For The Alboran Sea (Western Mediterranean)

A three dimensional biophysical model is employed to investigate the biological impacts of a meandering frontal jet for which the Alboran Sea of the Western Mediterranean is considered as a case study. The jet is characterized by relatively low density Atlantic water mass issuing from the Gibraltar Strait within the upper 100 m. It flows eastward as a highly nonlinear meandering current around the western and the eastern anticyclonic gyres prior to its attachment to the North African shelf/slope topography of the Algerian basin. Its inherent nonlinearity leads to the development of strong ageostrophic cross-frontal circulation that supplies nutrients into the nutrient-starved euphotic layer and stimulates an effective phytoplankton growth along the jet. The production intensity is strongest in the western basin and decreases eastwards with the gradual weakening of the jet. The stronger production intensity at the subsurface levels suggests the Alboran Sea is likely more productive than envisaged by the satellite chlorophyll data. The Mediterranean water mass away from the jet as well as the interior of the western and eastern anticyclonic gyres remain poorly productive.JRC.H.1-Water Resource

Mesoscale subduction at the Almeria-Oran front. Part 2: biophysical interactions.

This paper presents a detailed diagnostic analysis of hydrographic and current meter data from three, rapidly repeated, fine-scale surveys of the Almeria–Oran front. Instability of the frontal boundary, between surface waters of Atlantic and Mediterranean origin, is shown to provide a mechanism for significant heat transfer from the surface layers to the deep ocean in winter. The data were collected during the second observational phase of the EU funded OMEGA project on RRS Discovery cruise 224 during December 1996. High resolution hydrographic measurements using the towed undulating CTD vehicle, SeaSoar, traced the subduction of Mediterranean Surface Water across the Almeria–Oran front. This subduction is shown to result from a significant baroclinic component to the instability of the frontal jet. The Q-vector formulation of the omega equation is combined with a scale analysis to quantitatively diagnose vertical transport resulting from mesoscale ageostrophic circulation. The analyses are presented and discussed in the presence of satellite and airborne remotely sensed data; which provide the basis for a thorough and novel approach to the determination of observational error

PhoneSat In-flight Experience Results

Over the last decade, consumer technology has vastly improved its performances, become more affordable and reduced its size. Modern day smartphones offer capabilities that enable us to figure out where we are, which way we are pointing, observe the world around us, and store and transmit this information to wherever we want. These capabilities are remarkably similar to those required for multi-million dollar satellites. The PhoneSat project at NASA Ames Research Center is building a series of CubeSat-size spacecrafts using an off-the-shelf smartphone as its on-board computer with the goal of showing just how simple and cheap space can be. Since the PhoneSat project started, different suborbital and orbital flight activities have proven the viability of this revolutionary approach. In early 2013, the PhoneSat project launched the first triage of PhoneSats into LEO. In the five day orbital life time, the nano-satellites flew the first functioning smartphone-based satellites (using the Nexus One and Nexus S phones), the cheapest satellite (a total parts cost below $3,500) and one of the fastest on-board processors (CPU speed of 1GHz). In this paper, an overview of the PhoneSat project as well as a summary of the in-flight experimental results is presented

Integration of a MicroCAT Propulsion System and a PhoneSat Bus into a 1.5U CubeSat

NASA Ames Research Center and the George Washington University have developed an electric propulsion subsystem that can be integrated into the PhoneSat bus. Experimental tests have shown a reliable performance by firing three different thrusters at various frequencies in vacuum conditions. The three thrusters were controlled by a SmartPhone that was running the PhoneSat software. The subsystem is fully operational and it requires low average power to function (about 0.1 W). The interface consists of a microcontroller that sends a trigger pulses to the PPU (Plasma Processing Unit), which is responsible for the thruster operation. Frequencies ranging from 1 to 50Hz have been tested, showing a strong flexibility. A SmartPhone acts as the main user interface for the selection of commands that control the entire system. The micro cathode arc thruster MicroCAT provides a high 1(sub sp) of 3000s that allows a 4kg satellite to obtain a (delta)V of 300m/s. The system mass is only 200g with a total of volume of 200(cu cm). The propellant is based on a solid cylinder made of Titanium, which is the cathode at the same time. This simplicity in the design avoids miniaturization and manufacturing problems. The characteristics of this thruster allow an array of MicroCATs to perform attitude control and orbital correcton maneuvers that will open the door for the implementation of an extensive collection of new mission concepts and space applications for CubeSats. NASA Ames is currently working on the integration of the system to fit the thrusters and PPU inside a 1.5U CubeSat together with the PhoneSat bus into a 1.5U CubeSat. This satellite is intended to be deployed from the ISS in 2015 and test the functionality of the thrusters by spinning the satellite around its long axis and measure the rotational speed with the phone byros. This test flight will raise the TRL of the propulsion system from 5 to 7 and will be a first test for further CubeSats with propulsion systems, a key subsystem for long duration or interplanetary CubeSat missions

Micro Cathode Arc Thruster for PhoneSat: Development and Potential Applications

NASA Ames Research Center and the George Washington University are developing an electric propulsion subsystem that will be integrated into the PhoneSat bus. Experimental tests have shown a reliable performance by firing three different thrusters at various frequencies in vacuum conditions. The interface consists of a microcontroller that sends a trigger pulse to the Pulsed Plasma Unit that is responsible for the thruster operation. A Smartphone is utilized as the main user interface for the selection of commands that control the entire system. The propellant, which is the cathode itself, is a solid cylinder made of Titanium. This simplicity in the design avoids miniaturization and manufacturing problems. The characteristics of this thruster allow an array of CATs to perform attitude control and orbital correction maneuvers that will open the door for the implementation of an extensive collection of new mission concepts and space applications for CubeSats. NASA Ames is currently working on the integration of the system to fit the thrusters and the PPU inside a 1.5U CubeSat together with the PhoneSat bus. This satellite is intended to be deployed from the ISS in 2015 and test the functionality of the thrusters by spinning the satellite around its long axis and measure the rotational speed with the phone gyros. This test flight will raise the TRL of the propulsion system from 5 to 7 and will be a first test for further CubeSats with propulsion systems, a key subsystem for long duration or interplanetary small satellite missions