Top PDF High-Latitude Ocean Convection and Gyre Dynamics

High-Latitude Ocean Convection and Gyre Dynamics

High-Latitude Ocean Convection and Gyre Dynamics

all OCAPEs in this chapter are computed based on the full nonlinear equation of state of seawater (Jackett et al. 2006). OCAPE typically appears in an ocean col- umn when cold fresh water lies above warm salty water. This type of ocean column may be susceptible to TCC even if the column has a statically stable stratification. Thus TCC is not the regular surface buoyancy-driven convection. OCAPE o↵ers a main kinetic energy source for TCC and it arises from thermobaricitythe significant increase of the thermal expansion coefficient of seawater with the depth (Figure 3.2a). TCC is difficult to be directly observed due to its short timescales and severe polar ob- servational conditions during wintertime. However, indirect observational evidences and theoretical/numerical analysis suggest that the modern Weddell Sea is suscepti- ble to TCC (i.e., the release of OCAPE to kinetic energy) (detailed in Akitomo et al. 1995; Akitomo 1999, 2006; McPhee 2000, 2003; Harcourt 2005). OCAPE exists in the modern ocean: Figures 3.2c-d display a statically stable stratified profile with CFW overlying WSW that was observed in the Weddell Sea (McPhee et al. 1996). This profile contains a column-averaged OCAPE of 1.1 ⇥ 10 3 J kg 1 (equivalent to a
Show more

256 Read more

Anthropogenic carbon dynamics in the changing ocean

Anthropogenic carbon dynamics in the changing ocean

tinue to increase in the future, in contrast to other regions which will see a reduction or slow down of anthropogenic carbon uptake. We partly attribute this acceleration of up- take (i.e., in the high latitude Southern Ocean) to the effi- cient subsurface northward transport of anthropogenic car- bon into the intermediate waters. We also would like to stress the still considerable uncertainties about Southern Ocean car- bon cycling and its variations due to climate change. Lat- eral transports of anthropogenic carbon in most other re- gions (i.e., tropical regions) prominently occur within the surface or near-surface level. Therefore, they generally do not provide efficient deepwater pathways for export of an- thropogenic carbon.
Show more

10 Read more

A gridded data set of upper-ocean hydrographic properties in the Weddell Gyre obtained by objective mapping of Argo float measurements

A gridded data set of upper-ocean hydrographic properties in the Weddell Gyre obtained by objective mapping of Argo float measurements

Climatologies are generally constructed as mean oceano- graphic fields that represent a reference data set for a given period, which can then be used to derive temporal or spatial change across different scales or periods. Figure 23 shows the different time periods of a group of climatologies, as well as the gridded data sets provided here (hereafter WG_all, WG_TP1, WG_TP2 and WG_TP3, where “all” denotes the entire time period analysis and “TP” denotes the time period subsets). Table 2 provides the full name, regional boundary definitions and citations for each of the climatologies listed in Fig. 23. The closest matching time period to WG_all is WOA13, with a time span of 2005 to 2012 (“WOA13_0512” in Fig. 23); indeed WOA13 is the only climatology that will have incorporated the high-latitude float data of the Weddell Gyre, which provides improved spatial coverage of the upper 2000 m. The WG data sets are representative of smaller time periods, which may be helpful in the cross comparison with ship data and analysis of variability over smaller time periods (although users should exercise caution in the larger errors associated with WG13_TP1 due to data sparsity). The data source for the climatologies listed consists of historical data and more modern, higher-quality data (e.g. WOCE), combin- ing different data types (e.g. ship conductivity–temperature– depth (CTD) measurements, ship water sample, moorings, buoys, drifters and gliders). The WG data sets provide Argo-
Show more

26 Read more

Dynamics of Southern Ocean Mixed Layers

Dynamics of Southern Ocean Mixed Layers

Following earlier observational studies, we analyze the glider data for instances where the ocean is preconditioned towards gravitational and/or symmetric insta- bility in the mixed layer. Symmetric instability is a shear instability that extracts kinetic energy from geostrophic flows via slantwise convection. The resulting re- arrangement of water parcels leads to low PV in the mixed layer, conditioning it to further submesoscale instabilities (Haine and J. A. Marshall, 1998). We also inves- tigate the relative impacts of mixed layer baroclinic instability (BCI), which shoals the mixed layer by the slumping of isopycnals (Haine and J. A. Marshall, 1998), and Ekman buoyancy flux, or wind-driven re- and de-stratification (Thomas, 2005). When a wind stress is applied in a down-front orientation, the resulting Ekman transport carries denser water over lighter waters, causing vertical convection and a destruction of stratification and PV. When the wind has an up-front orientation, the Ekman transport moves lighter water over denser water, causing an increase in stratification throughout the Ekman layer depth, which can lead to a restratification of the mixed layer. Parameterizations are used to compare the potential effects of Ekman buoyancy flux and BCI on the mixed layer buoyancy budget. As in du Plessis et al. (2017), we use a 1-D mixed layer model to discern the role of surface forcing on setting upper ocean stratification. The model is then modified to incorporate the effects of Ekman buoyancy flux and BCI. Our results suggest that these processes are at least as important as the surface wind and buoyancy forcing in setting mixed layer variability in the Southern Ocean. Finally, a high-resolution global circulation model is used to validate our mixed layer observations and to confirm the feasibility of calculating PV from gliders.
Show more

106 Read more

Decadal variability of the subtropical gyre and deep meridional overturning circulation of the Indian Ocean

Decadal variability of the subtropical gyre and deep meridional overturning circulation of the Indian Ocean

We have described a new method for estimating the absolute velocity field across 32°S by combining hydrographic data with the barotropic flow from a global ocean model. For the 1987 section the estimate provides a flow field that is consistent with the estimate of MacDonald [1998] and much closer to hydrography-based estimates than many previous model-based studies. However, there are problems when the same technique is applied using the 2002 section. A ‘step-like’ feature in the isopycnals near 105°E creates a large vertical shear of meridional velocity and leads to net southward transport of the deep waters. This estimate is not considered realistic, but can be supported by the model dynamics, at least on decadal time scales. The peculiar flow field highlights the difficulty in trying to combine high-resolution hydrographic data with data from a 1°×1° global ocean model. As models increase in resolution and sophistication, the method outlined here may prove useful.
Show more

127 Read more

Plasma flow boundaries in the high latitude ionosphere

Plasma flow boundaries in the high latitude ionosphere

The main component of this thesis is to investigate ionospheric flow boundaries derived from plasma convection observations and their relationship to magnetospheric bound- aries. Observations of ionospheric boundaries can provide useful information on the time-dependant dynamics of the coupled solar wind-magnetosphere-ionosphere system. Ionospheric convection boundaries were inferred using an archive of data from the Su- perDARN HF radar network which operates in the auroral regions of both hemispheres. Regions where the ionospheric flow reveals a change in the east-west direction, the con- vection reversal boundary (CRB), is a common and widely-used criterion to identify boundaries in the convection data. However, this approach can be limited in certain regions. This thesis firstly presents a new boundary identification technique, the convec- tion curvature boundary (CCB) that is derived using a more physical interpretation of where boundaries in the convection data should lie. A statistical analysis is performed between the two different ionospheric boundaries and their applicability as a proxy for the open closed field line boundary (OCB) is tested. The CCB is found to be more robust than the CRB which tends to identify boundaries at unphysical latitudes, for ex- ample, close to the pole and at noon and midnight magnetic local times (MLTs) where it becomes less well defined. The noon region in particular shows that the CCB identifies boundaries at latitudes more consistent with theoretical considerations, especially when asymmetries are introduced into the ionospheric convection as a result of a B y -dominated
Show more

214 Read more

Phytoplankton distribution and nitrogen dynamics in the southwest indian subtropical gyre and Southern Ocean waters

Phytoplankton distribution and nitrogen dynamics in the southwest indian subtropical gyre and Southern Ocean waters

Coale, K. H., Johnson, K. S., Chavez, F. P., Buesseler, K. O., Bar- ber, R. T., Brzezinski, M. A., Cochlan, W. P., Falkowski, P. G., Bauer, J. E., Wanninkhof, R. H., Kudela, R. M., Altabet, M. A., Hales, B. E., Takahashi, T., Landry, M. R., Bidigare, R. R., Wang, X., Chase, Z., Strutton, P. G., Friederich, G. E., Gorbunov, M. Y., Lance, V. P., Hilting, A. K., Hiscock, M. R., Demarest, M., Hiscock, W. T., Sullivan, K. F., Tanner, S. J., Gordon, R. M., Hunter, C. N., Elrod, V. A., Fitzwater, S. E., Jones, J. L., Tozzi, S., Koblizek, M., Roberts, A. E., Brewster, J., Ladizinsky, N., Smith, G., Cooper, D., Timothy, D., Brown, S. L., Selph, K. E., Sheridan, C. C., Twining, B. S., and Johnson, Z. I.: Southern Ocean iron enrichment experiment: carbon cycling in the high- and low- Si waters, Science, 304, 408–414, 2004.
Show more

15 Read more

The great space weather washing machine:Examining the dynamics of high latitude ionosphere thermosphere coupling

The great space weather washing machine:Examining the dynamics of high latitude ionosphere thermosphere coupling

To begin the mapping process, LOS velocities from all available radars are mapped onto an equal area MLAT-MLON grid in AACGM coordinates (Shepherd, 2014). This is done by preforming a spatial and temporal boxcar filtering (taking into account radar scans before and after the scan of interest, as well as cells surrounding the target cell) with heavier weightings for data acquired within the cells themselves (Ruohoniemi and Baker, 1998). The gridded velocities are then translated to an MLAT-MLT grid, and overlapping vectors are merged using a least-squares linear regression akin to the merge technique by Cerisier and Senior (1994). For the potential to be fitted, a latitude where at least 3 LOS velocity vectors over 100 ms −1 lie is found in software, and a circular region is defined known as the Heppner-Maynard boundary (HMB) (Heppner and Maynard, 1987; Shepherd and Ruohoniemi, 2000). Here, the electric potential is assumed to be zero, and can be thought of as the limit of the convection pattern. Vectors which then happen to sit below the HMB are discarded.
Show more

149 Read more

On wind-driven mid-latitude convection in ocean general circulation models

On wind-driven mid-latitude convection in ocean general circulation models

Ocean general circulation models (OGCMs) adequately represent the formation of Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) in the Southern Ocean (England et al., 1993; Ribbe and Tomczak, 1997). The simulated mechanism is that of warm tropical and subtropical origin surface water being advected with the gyre scale circulation and the western boundary currents southward. Along its path eastward across the mid-latitude ocean, heat is lost from the surface layer. Density instabilities are subsequently adjusted by shallow convective overturn. Evidence of this mechanism as simulated by OGCMs is found in the correlation of regions which are characterized by both oceanic heat loss and convection in mid-latitudes of the Southern Ocean (England et al., 1993). These model results are consistent with observations. SAMW and AAIW are the end products of a water mass formation mechanism, which is driven by shallow mid-latitude convection in the Southern Ocean (McCartney, 1977 and 1982; Schodlok et al., 1997).
Show more

16 Read more

Dynamics of turbulent western-boundary currents at low latitude in a shallow-water model

Dynamics of turbulent western-boundary currents at low latitude in a shallow-water model

Current (SC), respectively. We refer the reader to Richard- son et al. (1994), Garzoli et al. (2003) and Fratantoni and Richardson (2006) for a detailed discussion of the NBC and the subtropical gyre in the Atlantic Ocean. A detailed de- scription of the circulation of the northern Indian Ocean, of which the SC is the most energetic part, is given by Schott and McCreary (2001), Schott et al. (2009), Beal and Dono- hue (2013) and Beal et al. (2013). These currents are vari- able in time. Part of this time dependence is due to the time- dependent wind forcing and the other part is due to the in- ternal dynamics of the ocean. In the present study we com- pletely neglect the former by using time-independent forc- ing, and the latter is the subject of the present publication. Even when subject to time-independent forcing, low lati- tude western-boundary currents retroflect (i.e., separate away from the boundary and turn anticyclonically for more than 90 ◦ ) and form anticyclonic eddies. The NBC retroflect near 6–8 ◦ N and sheds eddies exceeding 450 km in overall di- ameter (see, e.g., Richardson et al., 1994; Garzoli et al., 2003; Fratantoni and Richardson, 2006). The SC and the East African Coastal Current retroflect to form eddies called the Great Whirl (GW) between 5 and 10 ◦ N and the Southern Gyre (SG) near the Equator with overall diameter between 350 and 540 km (see, e.g., Schott and McCreary, 2001; Beal and Donohue, 2013; Beal et al., 2013). There are substantial differences between the near-surface circulation in the low latitude Atlantic and Indian Ocean, mainly due to the distinct wind forcing and coastline geometry.
Show more

11 Read more

Numerical modeling of solar wind influences on the dynamics of the high-latitude upper atmosphere

Numerical modeling of solar wind influences on the dynamics of the high-latitude upper atmosphere

An indirect mechanism of energy transfer from the solar wind to the upper atmosphere was recently brought up by Siscoe and Siebert (2006). It involves the Region–1 FAC system and the geomagnetic field configuration in such a way that the J ×B force acting against the solar wind at the high- altitude end of the Region–1 current loop is transmitted to the Earth as a J ×B force acting on the thermosphere (Siscoe, 2006). Vasyliunas (2007) compares this Lorentz force mech- anism as an analog to mechanical leveraging and quotes it the “mechanical advantage” of the magnetosphere in the M- I-T system, resulting in an increased thermospheric drag by nearly an order of magnitude over the direct drag mechanism. The thermospheric wind moves, on the other hand, the conducting ionized layers across the geomagnetic field lines, resulting in a neutral wind dynamo effect that contributes to the overall electrodynamics of the coupled system (Blanc and Richmond, 1980). Moreover, the inertia of the upper atmo- sphere’s motion can help to maintain the ionospheric convec- tion independently of the magnetospheric driver processes which is also known for long time as “fly-wheel effect” of the upper atmosphere (Banks, 1972; Coroniti and Kennel, 1973). The coupled M-I-T system will adjust the various driving processes to result in the plasma convection and ther- mospheric wind pattern, which we observe.
Show more

14 Read more

Light limitation of primary production in high latitude reservoirs

Light limitation of primary production in high latitude reservoirs

Woods and Onken (1982) showed the power of the Lagrangian ensemble approach to phytoplankton growth in ocean mixed layers by applying a random walk model to simulate plankton dynamics; thereafter, their approach was improved by Barkmann and Woods (1996). In the present study, a plankton model similar to the latter model was linked to the physical (Eulerian) reservoir model of the Akkajaure reservoir by Sahlberg (2003). However, the modified Langevin dispersion model used (Legg and Raupach, 1982) gives a better description of the dispersion process (Rahm and Svensson, 1986) as it is based on the k – e turbulence closure scheme (Rodi, 1980; Svensson, 1979) in the Akkajaure model. By using real weather data from neighbouring stations and light measurements in the reservoir, a good representation of the real PAR conditions was found. Further, by allowing for photo-adaption (Barkmann and Woods, 1996), the effect of changing light conditions was included. The time step in both the particle dispersion model and the photosynthesis model was short, 100 s, while it was 600 s in the reservoir model.
Show more

14 Read more

Quiet time magnetic variations at high latitude observatories

Quiet time magnetic variations at high latitude observatories

The quiet-time geomagnetic variations at high latitudes have not been systematically studied so far. Here we present quiet-time variation results from more than two years of continuous magnetic observations in Fennoscandia and Svalbard using the IMAGE magnetometer network. The CHAMP CO2 model is found to yield an excellent secular variation correction with a simple linear trend. The effect of the magnetospheric ring current on the quiet- time field values for each component is presented with the coefficients for the expected linear correlation with the D ST index. A general trend for these coefficients is found for the CGM latitudes from 54 to 68 degrees. In this area
Show more

19 Read more

Increasing vertical mixing to reduce Southern Ocean deep convection in NEMO3.4

Increasing vertical mixing to reduce Southern Ocean deep convection in NEMO3.4

(Fig. 3e) because of the brine rejection in the polynya and because deep salty waters have been brought up by convec- tion (Fig. 3d). Moreover, the increased convection reaches the layer of relatively warm waters, which enhance the warm anomaly at the surface (from January 1987; Fig. 3a) so that again the ocean surface is above freezing temperature when the sea ice should grow (Fig. 3b). Meanwhile, not only are the surface waters anomalously saline and dense because of brine rejection in winter, they also remain anomalously saline and dense through spring and summer (Fig. 3c, e), as no ice is available to be melted at the location of the polynya. As the surface waters are anomalously warm, the polynya reopens in July 1987 and reaches a maximum extent of 68 000 km 2 in October 1987 (Fig. 2d). This polynya reopens further south than the one in 1986. That is because the warm and dense anomalies have been advected in a near-barotropic subsur- face flow that brought them to the site of the 1987 polynya (Fig. 2e). Also, like real polynyas do (Smith and Barber, 2007), the 1986 model polynya and associated increased con- vection had an impact over a large area, lifting isopycnals sig- nificantly even at 66 ◦ S where a lower than usual sea ice con- centration can be seen (0.7 in the black contours of Fig. 2c).
Show more

12 Read more

The dynamics of convective orographic precipitation : the transition to convection

The dynamics of convective orographic precipitation : the transition to convection

methods were able to conserve the coarse resolution information while enhancing the small-scale variability, hence adding value to the original field. The transient estimation of the spectral scaling exponent resulted in better coherence between the sub-grid scale statistical structure and the respective coarse resolution information when the scaling behavior deviates significantly from the ensemble behavior. Additionally, the transient method also captured more accurately the high intensity rainfall statistics observed by a dense raingauge network, providing further support into the transient nature of the scaling behavior. Consequently StageIV_TF was chosen as representing the best fractal downscaling method and used to force hydrological simulations over the Pigeon River Basin in the Southern Appalachians. The hydrological simulations forced by the 1 km resolution ensemble averaged fractal downscaled fields overperformed the commonly used bilinear interpolation as expected. Non-fractal interpolation methods are unable to reproduce the subgrid-scale variability resulting in significant shortcoming in predicting extreme rainfall events associated with localized features, though the specific impact on skill metrics will necessarily depend on basin scale and geomorphic properties as well as the storm system proper. The results also show that the smooth character of the ensemble downscaled rainfall products resulting from averaging over several realizations cause an underestimation of the peak streamflow, particularly relevant for flashflood causing events extreme rainfall events such as the 2008 summer Tropical storm Fay case studied here. A more informative stochastic streamflow prediction was obtained by considering all the hydrological simulations forced by each of 50 single realizations of the fractal downscaled rainfall. The resulting spread of solutions was capable of capturing the observed intense streamflow peaks compared to the intrinsically smoother ensemble products. The stochastic forecasts were further enhanced by improving the resolution of fractal downscaled rainfall forcing to 250 m, resulting in reliable probabilistic forecasts and associated uncertainties with large value for extreme event forecasting and risk management.
Show more

151 Read more

Channelling of high-latitude boundary-layer flow

Channelling of high-latitude boundary-layer flow

showed that at Payerne, between the Jura Mountains and the Swiss Alps, shifts between channelled surface wind direc- tions statistically occur with overlying wind directions ap- proximately perpendicular to the predominant orientation of the valley. This suggests that under those circumstances cou- pling of different layers and turbulent momentum transfer from the overlying flow also plays an important role. As a re- sult, the ageostrophic component of channelled flow is min- imised. Weber and Kaufmann (1998) compared the relative importance of different forcing mechanisms for channelled flows in several Alpine valleys. They found that local wind conditions under the influence of essentially the same overly- ing flow can vary significantly between nearby locations, and are determined by differences in the local terrain, such as val- ley orientation, length, width, and depth. In particular, they found that winds in narrow valleys with widths of about 2– 3 km are more strongly affected by regional temperature gra- dients than in wider valleys. Also, in short and narrow valleys and with strong overlying flow, downward momentum trans- fer dominates the large-scale pressure gradient force. Based on measurements in the American Grand Canyon, the sig- nificance of large-scale pressure gradients for the forcing of winds in a mid-latitude valley under stable (wintertime) con- ditions relative to local thermal effects was also discussed by Whiteman et al. (1999). The dependence of mid-latitude val- ley flow on static stability was also shown by Klaus et al. (2003), who studied diurnal variations in near-surface wind directions within the Baar Basin of Germany, related to the varying importance of large-scale pressure gradients, local thermal forcing, and downward turbulent momentum trans- fer. In the presence of more complex terrain, such as within a bifurcating valley, splitting of channelled flow may occur (Drobinski et al., 2001; Drobinski et al., 2006).
Show more

20 Read more

Use of radio occultation to probe the high-latitude ionosphere

Use of radio occultation to probe the high-latitude ionosphere

Abstract. We have explored the use of COSMIC data to provide valuable scientific information on the ionospheric impacts of energetic particle precipitation during geomag- netic storms. Ionospheric electron density in the E region, and hence ionospheric conductivity, is significantly altered by precipitating particles from the magnetosphere. This has global impacts on the thermosphere–ionosphere because of the important role of conductivity on high-latitude Joule heating. Two high-speed stream (HSS) and two coronal mass ejection (CME) storms are examined with the COSMIC data. We find clear correlation between geomagnetic activity and electron density retrievals from COSMIC. At nighttime local times, the number of profiles with maximum electron den- sities in the E layer (below 200 km altitude) is well corre- lated with geomagnetic activity. We interpret this to mean that electron density increases due to precipitation are cap- tured by the COSMIC profiles. These “E-layer-dominant ionosphere” (ELDI) profiles have geomagnetic latitudes that are consistent with climatological models of the auroral lo- cation. For the two HSS storms that occurred in May of 2011 and 2012, a strong hemispheric asymmetry is observed, with nearly all the ELDI profiles found in the Southern, less sunlit, Hemisphere. Stronger aurora and precipitation have been ob- served before in winter hemispheres, but the degree of asym- metry deserves further study. For the two CME storms, oc- curring in July and November of 2012, large increases in the number of ELDI profiles are found starting in the storm’s main phase but continuing for several days into the recov- ery phase. Analysis of the COSMIC profiles was extended to all local times for the July 2012 CME storm by relaxing the ELDI criterion and instead visually inspecting all profiles above 50 ◦ magnetic latitude for signatures of precipitation in
Show more

12 Read more

The dynamics of open ocean plankton ecosystem models

The dynamics of open ocean plankton ecosystem models

As previously indicated, the Fasham (1993) model is only one of many which aim to capture the dynam- ics of plankton ecosystems. The various attempts fall across a continuum whose extremes can be broadly described by two approaches. At one extreme there are models, usually very complex models, which aim to faithfully (and quantitatively) represent the measured biological and physical processes occur- ring in the specic ecosystem in question. At the other extreme, there are models, usually much simpler models, which instead try to capture or explore the dynamics of key ecological pathways or relationships. Models at the former extreme tend to contain considerable biological and physical detail, are often built by ecologists familiar with the system, and usually are examined solely through numerical methods. While such models often compare favourably with particular data, it is usually very dicult to derive any general understanding of the model's behaviour which could aid its application in a dierent situ- ation ( i.e. the model begins to become as complicated as the situation under study). One of the best examples of this is the Narragansett Bay model from the monograph by Kremer & Nixon (1978). Woods & Barkmann's (1995) individual{based model (IBM) of zooplankton production in the North Atlantic (which uses the Lagrangian Ensemble method to track discrete plankton particles in a 3{dimensional volume) provides another example.
Show more

400 Read more

On deep convection events and Antarctic Bottom Water formation in ocean reanalysis products

On deep convection events and Antarctic Bottom Water formation in ocean reanalysis products

Changes in salinity and temperature in the Southern Ocean can be used as proxies to determine brine release, surface cooling and water mass entrainment during AABW forma- tion. Hence, the time series of those hydrographic proper- ties were analyzed to discuss the presence of the abovemen- tioned processes during bottom water formation. The aver- aged anomalies, which considered the long-term average of both temperature and salinity, were calculated for all ocean reanalysis products in three distinct layers: (i) a surface layer from 100 to 150 m, (ii) an intermediate layer from 400 to 650 m, and (iii) a bottom layer from 3000 m to the reanaly- sis seafloor. The depth limits of the three layers were chosen specifically due to their links with the processes being eval- uated (Orsi et al., 1999). The surface layer limits were cho- sen because their depths record the temperature and salinity signals related to brine release and surface cooling; the in- termediate limits are consistent with the depths of the deep waters and hence record the changes in the deep water prop- erties, and the bottom layer mainly records changes in the AABW, which constitutes most of the Southern Ocean below 3000 m. The temperature and salinity anomalies were calcu- lated for the Indian Ocean sector, the Western Pacific sector and the Weddell Sea sector due to the presence of AABW formation in those locations. Additionally, to make the time series of the variables comparable between the sectors, the data were normalized by their standard deviations since the inherent salinity and temperature of each layer are different for each sector. Those standardized anomalies provide an es- timate of how much the temperature and salinity deviate from the long-term average, which is a useful approach to identi- fying the low-frequency salinity and temperature changes in the time series, such as the ones related to AABW forma- tion. The annual and monthly time series of the standardized anomalies in each sector were analyzed, while focusing on the period and location of AABW formation to help explain the mechanisms involved in the formation. Finally, for a bet- ter description of the AABW formation process in UR025.4, we included analyses of the sea ice and ocean currents, all of which were provided by the reanalysis product.
Show more

22 Read more

STUDY OF SPACE WEATHER ON GPS PERFORMANCE AT LOW LATITUDE STATION BHOPAL AND HIGH LATITUDE STATION MAITRI, ANTARCTICA

STUDY OF SPACE WEATHER ON GPS PERFORMANCE AT LOW LATITUDE STATION BHOPAL AND HIGH LATITUDE STATION MAITRI, ANTARCTICA

magnetic equator by the Rayleigh-Taylor instability mechanism and then rise up and align along magnetic field lines propagating to higher latitude [17]. The irregularities while diffusing along field lines break into []mall patches which are observed in the form of scintillations with small patch duration at low latitudes [18]. Good overviews of scintillations at high and low latitude are recently given by [19].Geomagnetic and ionospheric storms generate significant large scale signatures in the TEC maps [20]. In particular differential TEC maps generated by subtracting monthly averages from actual TEC maps are helpful to draw conclusions concerning the nature of ionospheric storm processes. So the corresponding analysis of the storm on 21 st January, 2005 indicate both the action of an eastward directed electric field as well as the action of perturbation induced meridional winds in the thermosphere. The storm pattern provides a deeper insight into storm mechanisms and may be useful for an adequate modeling of ionospheric storm behavior in space weather forecast models. In addition to solar and geomagnetic activity indices TEC map derived ionospheric perturbation indices would be helpful especially for system operators to estimate the perturbation degree of the ionosphere.
Show more

10 Read more

Show all 10000 documents...