The steady‐state structure of the natural stratosphere and ozone distribution in a 2‐D model incorporating radiation and O‐H‐N photochemistry and the effects of stratospheric pollutants

A mean meridional circulation model of the stratosphere, incorporating radiative heating and photochemistry of the oxygen‐hydrogen‐nitrogen atmosphere, is used to simulate the meridional distributions of O₃, HO_X, N₂O,NO_X, temperature and the three components of mean motion for the summer and winter seasons under steady‐state conditions. The results are generally in good agreement with the available observations in the normal stratosphere. The model has been applied to assess the effects of water vapour and nitrogen oxide perturbations resulting from aircraft emissions in the stratosphere. It is found that a fleet of 500 Boeing‐type sst's, flying at 20 km and 45°N in the summer hemisphere and inserting NO_x at a rate of 1.8 megatons per year, has the effect of reducing the global total ozone by 14.7%. Similar calculations for 342 Concorde/TU‐114's, cruising at 17 km and injecting NO_x at a rate of 0.35 megatons per year, show a global‐average total‐ozone reduction of 1.85%. Although water vapour is considered important, because of its ability to convert NO₂ into HNO₃, the direct effect on global‐average total‐ozone reduction resulting from the 100% increase in the stratospheric water content is less than 1%. The changes in the chemical structure (HO^NO^), temperature, and mean motions associated with the ozone reduction are also investigated in the case of the 1.8‐megaton‐per‐year NO_X perturbation. It is shown that the reduced meridional temperature gradient in the middle and upper stratosphere resulting from the NO_x perturbation leads to the weakening of the tropical easterly jet in the summer hemisphere and mid‐latitude westerlies in the winter season.

The sensitivity of the model solutions to an alternate choice of input parameters (diffusion coefficients and solar photodissociation data) is tested and the main deficiency of the model is pointed out.     

A decision‐analytic study of the joint value of seasonal precipitation and temperature forecasts in a choice‐of‐crop problem

Abstract

A static decision‐analytic method is used to investigate the economic value of bivariate ‐ precipitation and temperature ‐ seasonal forecasts of the form currently issued by the U.S. National Weather Service. This method is applied to a corn versus spring wheat choice‐of‐crop decision‐making problem by considering a transect of four counties across the northwestern margin of the North American corn belt. Numerical results indicate that seasonal forecasts of current quality can be of appreciable value (≥$1/ha) for some locations when the optimal action chosen on the basis of climatological information is only marginally preferred to another action. Increases in forecast value follow from hypothetical increases in the quality of both the precipitation and temperature components of the forecasts in the spring wheat region, whereas forecast value increases primarily as a function of the quality of the precipitation forecasts alone in the corn belt region. The results are very sensitive to absolute and relative crop prices.     

Comparison and fusion of co‐occurrence,Gabor and MRF texture features for classification of SAR sea‐ice imagery

Abstract

Image texture interpretation is an important aspect of the computer‐assisted discrimination of Synthetic Aperture Radar (SAR) sea‐ice imagery. Co‐occurrence probabilities are the most common approach used to solve this problem. However, other texture feature extraction methods exist that have not been fully studied for their ability to interpret SAR sea‐ice imagery. Gabor filters and Markov random fields (MRF) are two such methods considered here. Classification and significance level testing shows that co‐occurrence probabilities classify the data with the highest accuracy, with Gaborfilters a close second. MRF results significantly lag Gabor and co‐occurrence results. However, the MRF features are uncorrelated with respect to co‐occurrence and Gabor features. The fused co‐occurrence/MRF feature set achieves higher performance. In addition, it is demonstrated that uniform quantization is a preferred quantization method compared to histogram equalization.     

Surface‐absorbed and top‐of‐atmosphere radiation fluxes for the Mackenzie River basin from satellite observations and a regional climate model and an evaluation of the model

Abstract

Both the earth‐reflected shortwave and outgoing longwave radiation (OLR) fluxes at the top of the atmosphere (TOA) as well as surface‐absorbed solar fluxes from Canadian Regional Climate Model (CRCM) simulations of the Mackenzie River Basin for the period March 2000 to September 2003 are compared with the radiation fluxes deduced from satellite observations. The differences between the model and satellite solar fluxes at the TOA and at the surface, which are used in this paper to evaluate the CRCM performance, have opposite biases under clear skies and overcast conditions, suggesting that the surface albedo is underestimated while cloud albedo is overestimated. The slightly larger differences between the model and satellite fluxes at the surface compared to those at the TOA indicate the existence of a small positive atmospheric absorption bias in the model. The persistent overestimation of TOA reflected solar fluxes and underestimation of the surface‐absorbed solar fluxes by the CRCM under all sky conditions are consistent with the overestimation of cloud fraction by the CRCM. This results in a larger shortwave cloud radiative forcing (CRF) both at the TOA and at the surface in the CRCM simulation. The OLR from the CRCM agrees well with the satellite observations except for persistent negative biases during the winter months under all sky conditions. Under clear skies, the OLR is slightly underestimated by the CRCM during the winter months and overestimated in the other months. Under overcast conditions the OLR is underestimated by the CRCM, suggesting an underestimation of cloud‐top temperature by the CRCM. There is an improvement in differences between model and satellite fluxes compared to previously reported results largely because of changes to the treatment of the surface in the model.     

Some properties and comparative performance of the semi‐Lagrangian method of Robert in the solution of the advection‐diffusion equation

Abstract

A numerical method for solving the advection‐diffusion equation, based on the semi‐Lagrangian algorithm of Robert (1981, 1982) is described, analysed and evaluated in comparison with other methods through a series of test problems. It is found that this method is generally better than other semi‐Lagrangian methods, and is a viable alternative to existing methods for LRTAP and other meteorological modelling because of its flexibility in application, its computational stability and its accuracy.     

Decadal‐to‐interdecadal fluctuations of arctic sea‐ice cover and the atmospheric circulation during 1954–1994

Abstract

The relationship between the Arctic and subarctic sea‐ice concentration (SIC) anomalies, particularly those associated with the decadal‐scale Greenland and Labrador Seas “Ice and Salinity Anomalies (ISAs) “, and the overlying atmospheric circulation fluctuations is investigated using the singular value decomposition (SVD) and composite map analysis methods. The data analyzed are monthly SIC and sea level pressure (SLP) anomalies, which cover the northern hemisphere poleward of 45°N and extend over the 41‐year period 1954–1994.

The SVD₁ (first) mode of the coupled variability, which accounts for 57% of the square covariance, is for the most part an atmosphere‐to‐ice forcing mode characterized by the decadal timescale. The aforementioned ISA anomalies are clearly captured by this mode whose SIC anomalies are dominated by a strong dipole across Greenland. However, as part of the same mode, there is also a weaker SIC dipole in the northern North Pacific which has opposite‐signed anomalies in the Sea of Okhotsk and the Bering Sea. It is also shown that there exists a significant negative correlation between the decadal SIC variability in the Greenland‐Barents Seas region associated with this mode and the North Atlantic Oscillation, whose spectrum also exhibits a quasi‐decadal signal.

The SVD₂ mode accounts for 12% of the square covariance and shows no evidence of a dominant forcing field of either SIC or SLP. This SVD mode exhibits very low frequency (interdecadal) variability, and its co‐variability is mainly concentrated in the northern North Pacific. It appears to be a high‐latitude extension of the recently investigated interdecadal North Pacific Oscillation. The spatial structure of the second mode complements the case of the first SVD mode whose co‐variability mainly occurs in the northern North Atlantic.     

Cross‐shore variations of near‐surface wind velocity and atmospheric turbulence at the land‐sea boundary during CASP

Abstract

Airborne measurements of mean wind velocity and turbulence in the atmospheric boundary layer under wintertime conditions of cold offshore advection suggest that at a height of 50 m the mean wind speed increases with offshore distance by roughly 20% over a horizontal scale of order 10 km. Similarly, the vertical gust velocity and turbulent kinetic energy decay on scales of order 3.5 km by factors of 1.5 and 3.2, respectively. The scale of cross‐shore variations in the vertical fluxes of heat and downwind momentum is also 10 km, and the momentum flux is found to be roughly constant to 300 m, whereas the heat flux decreases with height. The stability parameter, z/L (where z = 50 m and L is the local Monin‐Obukhov length), is generally small over land but may reach order one over the warm ocean. The magnitude and horizontal length scales associated with the offshore variations in wind speed and turbulence are reasonably consistent with model results for a simple roughness change, but a more sophisticated model is required to interpret the combined effects of surface roughness and heat flux contrasts between land and sea.

Comparisons between aircraft and profile‐adjusted surface measurements of wind speed indicate that Doppler biases of 1–2 m s^?1 in the aircraft data caused by surface motions must be accounted for. In addition, the wind direction measurements of the Minimet anemometer buoy deployed in CASP are found to be in error by 25 ± 5°, possibly due to a misalignment of the anemometer vane. The vertical fluxes of heat and momentum show reasonably good agreement with surface estimates based on the Minimet data.     

Sea‐ice interaction and the stability of the thermohaline circulation

Abstract

The role of sea‐ice in affecting the stability and long‐term variability of the oceanic thermohaline circulation (THC) is studied in this paper. The emphasis is placed on studying how sea‐ice might affect the stability and the long‐term variability of the THC through modulations of the surface heat and freshwater fluxes. A simple box model is analyzed to elucidate qualitatively the distinct physical meanings of these two processes. The analytical solution of this simple model indicates that, for the long timescales considered here, the thermal insulation stabilizes the THC while the freshwater feedback increases the effective inertia of the coupled ice‐ocean system. Sea‐ice insulation lessens the negative feedback between heat flux and the SST, and therefore, allows the SST to play a greater role in counteracting changes of the THC and high latitude salinity field. The freshwater feedback effectively links the surface heat flux to a freshwater reservoir, and thus, increases the effective inertia of the coupled ocean‐ice system. A two‐dimensional ocean model coupled with a thermodynamic sea‐ice model is used to estimate quantitatively the magnitudes of these two feedbacks. The numerical experiments involve the model's responses both to initial anomalies and to changes of forcing fields. For the free response cases (model responses to initial anomalies without changing the forcing fields), the model shows that the decay rate of an initial anomaly is greater when sea‐ice is included. For small perturbations the thermal insulation effect dominates over the freshwater feedback. The latter becomes increasingly more important for larger perturbations. In response to a change of external forcing, the presence of sea‐ice reduces the magnitude and the pace of the model's response. The numerical results are qualitatively consistent with the analytical solution of the box model.     

Reply to comments on and addenda to “some properties and comparative performance of the semi‐lagrangian method of Robert in the solution of the advection‐diffusion equation”

Abstract

Droughts are major natural disasters for many parts of the world. Dry areas, where the precipitation pattern is markedly seasonal, or is otherwise highly variable, are the most susceptible. The Canadian Prairies, together with the U.S. Great Plains, are one such area. While immediate loss of life is seldom a feature of most droughts, malnutrition and even starvation do follow severe droughts in some parts of the world. In Canada, economic losses, particularly in the agricultural sector, may reach several hundred millions of dollars in a drought year, with major socio‐economic repercussions affecting the entire region. Environmental damages include soil degradation and erosion, vegetation damage, slough and lake deterioration and wildlife loss. Unlike most other natural disasters, drought onset is difficult to identify. Droughts develop slowly, and until human activity begins to be affected by an on‐going reduction of precipitation, their existence is unrecognized. Development and application of specific soil moisture and drought indices based on cumulative precipitation deficits have enhanced drought monitoring programs. These in turn provide guidance on the need for mitigative measures that can be initiated early in the course of a drought. Any improvement in the timely application of these measures is, however, strongly dependent on being able to determine the drought's course, extent and likely severity at the earliest stage possible. The identification of precursor conditions for past drought has raised the possibility that the likelihood of a drought occurring in a particular year or growing season might be predictable. Teleconnections between North American precipitation patterns and ENSO events and other surface boundary conditions in the North Pacific have been detected. Forecasting seasonal temperature and perhaps precipitation anomalies appears to be potentially feasible using a suitable merging of precursor parameters and modelling methodologies. Clearly, future research must focus both on those precursors that have been identified and on a search for possible new ones. Development of better forecasting methodology is also essential. Research activity to identify and evaluate new mitigative measures should also be increased to keep pace with the prospects of drought predictability.     

Ground‐based measurements of ozone and NO2 during MANTRA 1998 using a Zenith‐sky spectrometer

Abstract

A portable ground‐based instrument has been constructed for the automated measurement of vertical column abundances of a number of gases pertinent to stratospheric ozone chemistry. The instrumentation is described in this paper and results are presented from the first set of field measurements, made during the Middle Atmosphere Nitrogen TRend Assessment (MANTRA) 1998 field campaign at Vanscoy, Saskatchewan, Canada. Zenith‐sky spectra in the near ultraviolet and visible wavelength regions were recorded for a period of seven days, prior to and following the launch of the MANTRA balloon on 24 August 1998. The spectra were then analysed using the differential optical absorption spectroscopy (DOAS) technique in conjunction with a radiative transfer model to determine vertical column amounts of ozone and NO₂. Ozone measurements compared favourably with concurrent observations by ozonesondes, a Brewer spectrophotometer, and satellite instruments. Vertical NO₂ columns were in broad agreement with those determined by the Global Ozone Monitoring Experiment (GOME) satellite instrument.     

A note on the break‐up of lakes and rivers as indicators of climate change

Abstract

A detailed examination has been made of the relationship between the space and time variations of the Indian summer monsoon rainfall and the equatorial eastern‐Pacific sea surface temperature (SST) anomaly in different seasons for the 108‐year period, 1871–1978. There is a strong inverse relationship between the two. The correlation coefficients between All‐India monsoon rainfall and the sea surface temperature anomaly for the concurrent season; June, July and August (JJA) and for the succeeding seasons; September, October and November (SON) and December, January and February (DJF) are consistently and highly significant. Even a random sample of 50 years gave values significant at the 0.1 percent level. The sliding window correlation analysis of 10‐, 20‐ and 30‐year widths indicates that the relationships between All‐India monsoon rainfall and the sea surface temperature anomaly for the concurrent JJA and the succeeding SON and DJF seasons exhibit stability and consistency in significance. For contiguous meteorological sub‐divisions west of longitude 80°E the relationship is highly significant for JJA and for succeeding SON and DJF seasons.     

On the variable‐lag and variable‐velocity cell‐to‐cell routing schemes for climate models

Abstract

The cell‐to‐cell channel routing schemes used in General Circulation Models (GCMs) and Regional Climate Models (RCMs) are revisited. A simpler parsimonious routing scheme based on Askew's formula (1970) for computing time‐evolving channel lags is implemented and tested against observations and compared with the variable‐velocity scheme of Arora and Boer (1999). The variable‐lag routing scheme agrees very well with the variable‐velocity scheme. The variable‐lag scheme has the advantage of using fewer parameters, which is a major advantage at fine resolution over a large domain, where the uncertainty associated with parameters can be quite large.

The spatial resolutions of RCMs are much finer than those of GCMs and hence there is a need for channel routing at fine spatial resolutions. The task of extending the cell‐to‐cell routing schemes developed for large‐scale routing, as in GCMs, to finer spatial scales, as in RCMs, is addressed. The sensitivity of the variable‐lag scheme to the routing time interval is studied. The choice of the routing time interval is very critical and varies with the spatial resolution as in any hydrological model. A simple method for determining the appropriate range of routing intervals at different spatial resolutions for the variable‐lag scheme is presented.     

On tidal resonance in the global ocean and the back‐effect of coastal tides upon open‐ocean tides

Abstract

The resonance of semi‐diurnal tidal elevations is investigated with a forward numerical forced damped global tide model and an analytical model of forced‐damped tides in a deep ocean basin coupled to a shelf. The analytical model contains the classical half‐wavelength and quarter‐wavelength resonances in the deep ocean and shelf, respectively, as well as a forcing‐scale dependence which depends on the ratio of the phase speed of open‐ocean gravity waves to that of the astronomical forcing. In the analytical model, when the deep ocean and shelf resonate separately at the same frequency, the resonance in the coupled system shifts to frequencies slightly higher and lower than the original frequency, such that a ‘double bump’ is seen in plots of elevation amplitude versus frequency. The addition of a shelf to a resonant open ocean tends to reduce open‐ocean tides, especially when the shelf is also near resonance. The magnitude of this ‘back‐effect’ is controlled by shelf friction. A weakly damped resonant shelf has a larger back‐effect on the open‐ocean tide than does a strongly damped shelf. Numerical simulations largely bear out the analytical model predictions, at least qualitatively. Idealized simulations show that continents enhance tides by enabling the half‐wavelength resonance. Simulations with realistic geometry and topography but varying longitudinal structure in the astronomical forcing display an influence of the forcing scale on tidal amplitudes somewhat similar to that seen in the analytical model. A frequency sweep in the semi‐diurnal band in experiments with realistic geometry and topography reveals weakly resonant peaks in the amplitudes of several shelf regions and in the globally averaged open‐ocean amplitudes. Finally, the back‐effect of the shelf upon the open ocean is seen in simulations in which locations of resonant coastal tides are blocked out and open‐ocean tidal elevations are significantly altered (increased, generally) as a result.     

The delineation of rain areas from visible and IR satellite data for GATE and mid‐latitudes

Abstract

Two‐dimensional pattern matching has been used to delineate raining areas of clouds from GATE and Montreal GOES visible and IR satellite data, with radar as ground truth. For the cases examined, the cloud cover was of the order of 4 times larger than the rain area, requiring skill to separate out low‐thick or high‐thin non‐precipitating clouds from cumulus systems, which is difficult using a single threshold. The more flexible approach described here has allowed useful rain maps to be generated for all the types of weather systems examined. The optimum boundary separating raining from non‐raining areas is relatively insensitive to diurnal and day‐to‐day variations, but is different for the tropical Atlantic and for Montreal.     

The circulation and residence time of the strait of Georgia using a simple mixing‐box approach

Abstract

New observations in the Strait of Georgia, British Columbia, Canada show that temperature and dissolved oxygen have a pronounced seasonal cycle, with a spatially varying phase. Phase lags in oscillating systems arise due to internal time scales which can be interpreted in fluid systems as residence times. Exploiting phase we construct a quantitative and internally consistent circulation scheme for this body of water after dividing it into four regions: the Fraser River plume, the surface waters down to 50 m, the intermediate waters down to 200 m, and the deep water. In this scheme the intermediate water, the largest region by volume, is continually renewed, and its characteristics change in response to continuous changes in the characteristics of source waters. The dependence of the estuarine circulation on variations in fresh inflow is weak. The deep water is volumetrically less important, but seasonal changes in the density of oceanic source waters can produce a variation in the overall circulation by driving an additional inflow which leads to both deep renewal and increased upwelling. In turn, this increased upwelling results in lower surface temperatures than might otherwise be expected. Intermediate water residence times are about 160 days. Deep water is renewed once per year in summer and is affected only by vertical diffusion during the rest of the year. Surface water residence times for the entire Strait are a few months at most, but the Fraser River plume has a freshwater residence time of approximately 1 day. In addition, we find that the residence time of oceanic source waters in the Strait is 1.7 years due to a substantial recirculation in Haro Strait. Other consequences of this scheme are consistent with independent estimates of horizontal transports, air‐sea heat fluxes, subsurface oxygen (O₂) utilization, and primary production. Finally, analysis of the spatial phase variations suggests that the intermediate inflow enters the Strait as a boundary current along the slopes of the Fraser delta.     

A 9‐year summary of radar characteristics of mesocyclonic storms and of deep convection in southern Québec

Abstract

Nine summers of reflectivity and Doppler data, (1993–2001), archived by the Marshall Radar Observatory of McGill University have been processed for the purpose of identifying the location, strength and frequency of occurrence of severe weather events associated with convective activity. A mesocyclone detection and tracking algorithm has identified 329 features with a lifetime of at least 10 minutes. The distribution of their duration, path length, diameter, depth, rotational velocity and shear are provided, as well as their hourly and monthly frequency. Their geographical distribution reveals an increased relative probability of occurrence over the western area of the McGill radar coverage as well as to the north, near Mirabel, and a reduced probability of occurrence near the metropolitan area of Montréal.

The analysis of deep convection has been performed in terms of upper level Vertically Integrated Liquid water content maps (UVIL) where the vertical integration of reflectivity begins at a height of 5 km. UVIL maps are preferred among other types of reflectivity‐based radar products because they are the least affected by radar artefacts such as bright band, ground echoes, anomalous propagation and beam blocking. An inherent bias, present in the standard generation of UVIL maps, and due to an oxygen attenuation overcorrection and to the vertical profile of reflectivity of thunderstorms as sampled by a broadening beamwidth, has been identified and corrected. The geographical distribution of UVIL measurements in terms of the time that a UVIL threshold of 10 and 15 kg m^?2 is exceeded has been obtained for both the individual years and for the entire 9‐year period. Areas of preferred convection have been identified in the latter, particularly along the flatlands of the St. Lawrence River Basin. A relative minimum is quite noticeable along a broad corridor running north and south of the radar over heavily forested mountainous regions. This combination results in a non‐negligible correlation of the order of ‐0.2 between the height of the topography (m) and deep convection. Curves revealing the relative severity of the nine years in terms of a continuous UVIL threshold have also been derived. The years 1994, 1998 and 1999 emerged as the most active years while 1996 and 2000 were clearly very quiet.     

Phase‐locked and asymmetric correlations of the wintertime atmospheric patterns with the ENSO

Abstract

Teleconnections between sea surface temperature (SST) anomalies over the Pacific and the dominant patterns of wintertime Northern Hemisphere 500‐hPa height are examined by applying statistical techniques such as rotated principal component analysis and composite analysis. It is shown that the Pacific/North American (PNA) patterns in December through March are correlated most significantly with the ENSO‐related SST anomalies in the previous October, while the western Pacific (WP) patterns in December through February are most closely linked to the ENSO‐related SST anomalies in the same season. In addition, the PNA response to the ENSO signal during La Niña events is more significant than that during El Niño events, while the WP response is stronger during El Niño events than during La Niña events. A composite analysis shows that in the El Niño winters the North Pacific centre of the PNA pattern is located about 10 degrees east of its normal position, leading to a less significant correlation between the ENSO signal and the PNA pattern in these winters.

The ENSO‐related SST anomalies include a large centre of action over the tropical Pacific and an oppositely signed anomaly centre over the North Pacific. The North Pacific centre appears to the west of the dateline in September and October. This ENSO‐related seed of SST anomalies slowly moves eastward in the following months, gradually cutting off its connection with SST anomalies over the tropical Pacific and being coupled with the PNA pattern. It is pointed out that, although the wintertime SST anomaly over the North Pacific may appear as a mode linearly independent of the ENSO signal in the same season, it is partially related to the ENSO signal in the preceding autumn.

Possible dynamical explanations of the above results are discussed. It is suggested that the WP pattern can be linked to the tropical Pacific heat source via advection of vorticity by the upper‐tropospheric divergent/convergent flow, and the intensification of vorticity gradients associated with a stronger east Asian jet is likely to be responsible for a more significant WP pattern response to the ENSO signal in the El Niño winters. On the other hand, the ENSO‐related PNA pattern could be considered a manifestation of the eastward extension (El Niño) or westward withdrawal (La Niña) of the east Asian jet stream due to the local Hadley cell over the Pacific. In addition, the ENSO‐related seed of extratropical SST anomaly over the western Pacific in autumn may also play an important role in the development of the PNA pattern in the following winter.     

C‐band SAR backscatter characteristics of Arctic sea and land ice during winter

Abstract

Synthetic Aperture Radar (SAR) data has become an important tool for studies of polar regions, due to high spatial resolution even during the polar night and under cloudy skies. We have studied the temporal variation of sea and land ice backscatter of twenty‐four SAR images from the European Remote Sensing satellite (ERS‐1) covering an area in Lady Ann Strait and Jones Sound, Nunavut, from January to March 1992. The presence of fast ice in Jones Sound and glaciers and ice caps on the surrounding islands provides an ideal setting for temporal backscatter studies of ice surfaces. Sample regions for eight different ice types were selected and the temporal backscatter variation was studied. The observed backscatter values for each ice type characterize the radar signatures of the ice surfaces. This time series of twenty‐four SAR images over a 3‐month period provides new insights into the degree of temporal variability of each surface. Ice caps exhibit the highest backscatter value of ‐3.9 dB with high temporal variability. Valley glacier ice backscatter values decrease with decreasing altitude, and are temporally the most stable, with standard deviations of 0.08–0.10 dB over the 90‐day period.

First‐year ice and lead ice show a negative trend in backscatter values in time and a positive correlation of up to 0.59 with air temperature over the 90‐day period. For first‐year ice and lead ice, episodes of large temperature fluctuations (±12°C) are associated with rapid changes in backscatter values (±2 dB). We attribute the backscatter increase to a temperature‐induced increase in brine volume at the base of the snow pack. Multi‐year ice, conglomerate ice and shore ice are relatively stable over the 3‐month period, with a backscatter variation of only a few dBs. An observed lag time of up to three days between backscatter increase/decrease and air temperature can be attributed to the insulation effect of the snow cover over sea ice. The net range of the backscatter values observed on the most temporally stable surface, valley glacier ice, of about 0.30 dB indicates that the ERS‐1 SAR instrument exceeds the 1 dB calibration accuracy specified for the Alaska SAR Facility processor for the three winter months.     

The influence of Hudson Bay runoff and ice‐melt on the salinity of the inner Newfoundland Shelf

Abstract

The present study examines sources of the interannual variability in salinity on the Newfoundland continental shelf observed in a 40‐year time series from an oceanographic station known as Station 27. Specifically, we investigate, through lag‐correlation analysis, the a priori hypotheses that the salinity anomalies at Station 27 are determined by freshwater runoff anomalies from Hudson and Ungava bays and by ice‐melt anomalies in Hudson Bay and on the Labrador Shelf. Interannual variations of summer runoff into Hudson Bay were significantly negatively correlated with salinity anomalies on the Newfoundland Shelf with a lag (9 months) that is consistent with expected travel times based on known current velocities in Hudson Bay and along the Labrador Shelf. Sea‐ice extent over the Labrador and northern Newfoundland shelves was significantly negatively correlated with salinity at a lag of 3 to 4 months, corresponding to the time of minimum salinity at Station 27. It appears that ice‐melt over the Labrador‐northern Newfoundland Shelf is primarily responsible for the seasonal salinity minimum over the Newfoundland Shelf. Interannual variability in runoff into Ungava Bay and ice‐melt in Hudson Bay were not correlated with interannual salinity variations on the Newfoundland Shelf.