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H. M. de Jong

Abstract

The present system of evaluating upper winds by means of radar/radio tracking of pilot and radiosonde balloons is in its most general form to be considered as an overdetermined observation system. The redundancy of information in such systems may be used to improve the overall precision of measurement by applying the well-known theory of adjustment of observations. In this paper a scheme for computation is presented, not only for the case of a flat earth, but also for the case including the effect of the earth's curvature. The scheme is particularly feasible for implementation in practice by means of electronic data processing.

The proposed scheme has the advantage that the numerical process also incorporates the conventional modes of operation. Apart from an adjustment procedure a simple smoothing process is described which depends on the accuracy attainable by the measuring technique. This effectuates a partial separation of the instrumental errors from real wind fluctuations. Some numerical data give an impression of the gain in accuracy and the effect of a certain amount of smoothing.

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H. M. de Jong

Abstract

The evaluation of upper-level wind data by means of balloon-tracking methods involves a number of determinative and random errors. These errors depend on the precision in locating the points of the balloon track, which in their turn are related to the accuracy of measuring quantities such as azimuth, elevation angle, slant range, balloon height, and time.

Since the number of quantities needed for plotting the horizontal projection of the balloon's track by radar systems is supernumerary, the observations may be arranged in three classes. The purpose of this paper is to determine which of these classes yields the best precision of measure in wind speed and direction.

Moreover the errors are considered as a function of balloon height, wind speed, rate of ascent and time interval between two successive measured points. For special cases the extreme values of the random errors dependent on the location of the balloon's trajectory with regard to the direction of observation is presented in the form of tables.

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H. M. De Jong

Abstract

The position of a pilot balloon or any other airborne target which is followed by two theodolites is usually computed by means of the known baselength (i.e., the distance between the two theodolite stations) and three observed angle readings. It is to be noted, however, that four angle readings are available. In order to obtain an optimum estimation of the target's location the theory of adjustment of observations should be applied. With this method the estimation of the location is based on making the magnitude of the (root mean square) error a minimum. The method is particularly suitable for high speed electronic computers. The error analysis makes it possible to give some valuable hints in planning specific experiments with two optical or radio theodolites.

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M. F. de Jong
,
A. S. Bower
, and
H. H. Furey

Abstract

Between 25 September 2007 and 28 September 2009, a heavily instrumented mooring was deployed in the Labrador Sea, offshore of the location where warm-core, anticyclonic Irminger rings are formed. The 2-year time series offers insight into the vertical and horizontal structure of newly formed Irminger rings and their heat and salt transport into the interior basin. In 2 years, 12 Irminger rings passed by the mooring. Of these, 11 had distinct properties, while 1 anticyclone likely passed the mooring twice. Eddy radii (11–35 km) were estimated using the dynamic height signal of the anticyclones (8–18 cm) together with the observed velocities. The anticyclones show a seasonal cycle in core properties when observed (1.9°C in temperature and 0.07 in salinity at middepth) that has not been described before. The temperature and salinity are highest in fall and lowest in spring. Cold, fresh caps, suggested to be an important source of freshwater, were seen in spring but were almost nonexistent in fall. The heat and freshwater contributions by the Irminger rings show a large spread (from 12 to 108 MJ m−2 and from −0.5 to −4.7 cm, respectively) for two reasons. First, the large range of radii leads to large differences in transported volume. Second, the seasonal cycle leads to changes in heat and salt content per unit volume. This implies that estimates of heat and freshwater transport by eddies should take the distribution of eddy properties into account in order to accurately assess their contribution to the restratification.

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M. F. de Jong
,
A. S. Bower
, and
H. H. Furey

Abstract

The contribution of warm-core anticyclones shed by the Irminger Current off West Greenland, known as Irminger rings, to the restratification of the upper layers of the Labrador Sea is investigated in the 1/12° Family of Linked Atlantic Models Experiment (FLAME) model. The model output, covering the 1990–2004 period, shows strong similarities to observations of the Irminger Current as well as ring observations at a mooring located offshore of the eddy formation region in 2007–09. An analysis of fluxes in the model shows that while the majority of heat exchange with the interior indeed occurs at the site of the Irminger Current instability, the contribution of the coherent Irminger rings is modest (18%). Heat is provided to the convective region mainly through noncoherent anomalies and enhanced local mixing by the rings facilitating further exchange between the boundary and interior. The time variability of the eddy kinetic energy and the boundary to interior heat flux in the model are strongly correlated to the density gradient between the dense convective region and the more buoyant boundary current. In FLAME, the density variations of the boundary current are larger than those of the convective region, thereby largely controlling changes in lateral fluxes. Synchronous long-term trends in temperature in the boundary and the interior over the 15-yr simulation suggest that the heat flux relative to the temperature of the interior is largely steady on these time scales.

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Heather H. Furey
,
M. Femke de Jong
,
James R. Valdes
, and
Amy S. Bower

Abstract

Two submerged autonomous launch platforms (SALPs) were deployed at 500-m depth on a deep-water mooring in the northeastern Labrador Sea from 2007 to 2009 to automatically release profiling floats into passing warm-core anticyclonic Irminger Rings (IRs). The objective was to investigate the rings’ vertical structure and evolution as they drifted from their formation site near the western coast of Greenland to the area of deep convection in the south-central part of the basin. Mechanically and electronically, the SALP worked well: 10 out of 11 floats were successfully released from the mooring over 2 years. However, getting floats trapped in eddy cores using a preprogrammed release algorithm based on temperature and pressure (a proxy for current speed) measured by the SALPs met with limited success mainly because 1) the floats settled at a park pressure that was initially too deep, below the volume of water trapped in the eddy core; 2) the eddies translated past the mooring much more quickly than anticipated; and 3) there is a seasonal cycle in both background and eddy core temperature that was not known a priori and therefore not accounted for in the release algorithm. The other mooring instruments (100–3000 m) revealed that 12 anticyclones passed by the mooring in the 2-yr monitoring period. Using this independent information, the authors assessed and improved the release algorithm, still based on ocean conditions measured at one depth, and found that much better performance could have been achieved with an algorithm that allowed for faster eddy translation rates and the seasonal temperature cycle.

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M. F. de Jong
,
S. S. Drijfhout
,
W. Hazeleger
,
H. M. van Aken
, and
C. A. Severijns

Abstract

The performance of coupled climate models (CCMs) in simulating the hydrographic structure and variability of the northwestern North Atlantic Ocean, in particular the Labrador and Irminger Seas, has been assessed. This area plays an important role in the meridional overturning circulation. Hydrographic properties of the preindustrial run of eight CCMs used in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) are compared with observations from the World Ocean Circulation Experiment Repeat section 7 (WOCE AR7). The mean and standard deviation of 20 yr of simulated data are compared in three layers, representing the surface waters, intermediate waters, and deep waters. Two models simulate an extremely cold, fresh surface layer with model biases down to −1.7 psu and −4.0°C, much larger than the observed ranges of variability. The intermediate and deep layers are generally too warm and saline, with biases up to 0.7 psu and 2.8°C. An analysis of the maximum mixed layer depth shows that the low surface salinity is related to a convective regime restricted to the upper 500 dbar. Thus, intermediate water formed by convection is partly replaced by warmer water from the south. Model biases seem to be caused by the coupling to the atmospheric component of the CCM. Model drift during long spinup periods allows the initially small biases in water mass characteristics to become significant. Biases that develop in the control run are carried over to the twentieth-century runs, which are initialized from the control runs.

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