Amir Shabbar

Canadian Precipitation Patterns Associated with the Southern Oscillation

Abstract Precipitation responses over Canada associated with the two extreme phases of the Southern Oscillation (SO), namely El Nino and La Nina, are identified. Using the best available precipitation data from 1911 to 1994, both the spatial and temporal behavior of the responses are analyzed from the El Nino/La Nina onset to several seasons afterward. Composite and correlation analyses indicate that precipitation over a large region of southern Canada extending from British Columbia, through the prairies, and into the Great Lakes region is significantly influenced by the SO phenomenon. The results show a distinct pattern of negative (positive) precipitation anomalies in this region during the first winter following the onset of El Nino (La Nina) events. During this same period, significant positive precipitation anomalies occur over the northern prairies and southeastern Northwest Territories in association with El Nino events. Statistical significance of the responses is tested by the Student’s t-test a...

The relationship between the North Atlantic Oscillation and El Niño‐Southern Oscillation

We have applied a multiresolution cross-spectral analysis technique to resolve the temporal relationship between the NAO and ENSO. The study shows significant coherence between NAO and Nino3 SST in about 70% of the warm ENSO events from 1900 to 1995, of which 33% and 37% are associated with a 5- to 6-year period (E1) and a 2- to 4-year period (E2) oscillation terms in the spectral decomposition, respectively. The dominant teleconnection pattern associated with changes in the mean atmospheric circulation during the initial winter of a typical E1 and E2 events is the positive phase of the Pacific/North American (PNA) pattern. Non-coherence between the NAO and ENSO occurs during relatively weak Nino3 SST anomaly, with a teleconnection pattern which shows a strong negative phase of the NAO and a pattern which resembles a weak eastward shifted negative phase of the PNA pattern.

Summer Drought Patterns in Canada and the Relationship toGlobal Sea Surface Temperatures

Abstract Canadian summer (June–August) Palmer Drought Severity Index (PDSI) variations and winter (December– February) global sea surface temperature (SST) variations are examined for the 63-yr period of 1940–2002. Extreme wet and dry Canadian summers are related to anomalies in the global SST pattern in the preceding winter season. Large-scale relationships between summer PDSI patterns in Canada and previous winter global SST patterns are then analyzed using singular value decomposition (SVD) analysis. The matrix for the covariance eigenproblem is solved in the EOF space in order to obtain the maximum covariance between the singular values of the SST and the PDSI. The robustness of the relationship is established by the Monte Carlo technique, in which the time expansion of the primary EOF analysis is shuffled 1000 times. Results show that the leading three SVD-coupled modes explain greater than 80% of the squared covariance between the two fields. The interannual El Nino–Southern Oscillation (ENSO), the ...

The impact of el Nino‐Southern oscillation on the temperature field over Canada: Research note

Abstract The impact of the two phases of El Nino‐Southern Oscillation (ENSO), namely El Nino and La Nina, on the surface and lower tropospheric temperature fields over Canada is documented. Gridded surface temperature data for 91 years (1900–1990) and 500–1000 hPa thickness data for 49 years (1946–1994) have been analyzed statistically in the context of El Nino, La Nina and normal years. Using a composite analysis, the present study conclusively demonstrates that significant positive surface temperature anomalies spread eastward from the west coast of Canada to the Labrador coast from the late fall to early spring (November through May) following the onset of El Nino episodes. The accompanying temperatures in the lower troposphere show a transition from the Pacific/North American (PNA) pattern to the Tropical/Northern Hemisphere (TNH) pattern over the North American sector during the same period. Conversely, significant negative surface temperature anomalies spread southeastward from the Yukon and extend ...

An Assessment of changes in winter cold and warm spells over Canada

The recent Third Assessment Report (TAR) of the Intergovernmental Panel onClimate Change (IPCC) indicated that observed 20th century changes in severalclimatic extremes are qualitatively consistent with those expected due to increasedgreenhouse gases. However, a lack of adequate data and analyses make conclusiveevidence of changing extremes somewhat difficult, particularly, in a global sense.In Canada, extreme temperature events, especially those during winter, can havemany adverse environmental and economic impacts. In light of the aforementionedIPCC report, the main focus of this analysis is to examine observed trends andvariability in the frequency, duration, and intensity of winter (Jan–Feb–Mar) cold and warm spells over Canada during the second half of the 20th century.Cold spell trends display substantial spatial variability across the country. From1950–1998, western Canada has experienced decreases in the frequency, duration, and intensity of cold spells, while in the east, distinct increases in the frequency and duration have occurred. These increases are likely associated with morefrequent occurrences of the positive phase of the North Atlantic Oscillation (NAO)during the last several decades. With regard to winter warm spells, significantincreases in both the frequency and duration of these episodes were observedacross most of Canada. One exception was found in the extreme northeasternregions, where warm spells are becoming shorter and less frequent. The resultsof this study are discussed within the context of climate warming expectations.

The association between the BWA index and winter surface temperature variability over eastern Canada and west Greenland

Since about 1970, winter surface temperature data from stations on coastal eastern Canada and western Greenland have shown detectable decadal cooling. In this study, we attempt to understand some aspect of this surface cooling trend by relating it to the variability of the Canadian Polar Trough (CPT). In order to facilitate the relationship, we introduce a new 50 kPa index called the Baffin Island–West Atlantic (BWA) index which, although reflecting the variability of the western structure of the North Atlantic Oscillation (NAO), is found to explain temperature variability better in north-eastern North America than the structure characterized by the NAO index. The decadal variability in the winter surface temperature is found to be associated with the BWA index at a statistically significant correlation of 0·85. Two distinctive winter climate regimes are found to exist in the climate record from 1947 to 1995, one before and one after about 1970. Although the magnitude of the variance does not change significantly from one regime to the next, the two regimes are characterized by statistically significantly different means and by two distinct spectral signatures. Variability before 1970 is dominated by interannual fluctuations, whereas afterwards much of the contribution to the variability comes from interdecadal fluctuations. Subtraction of the 1947–1969 winter 50 kPa mean height field from the 1970–1995 mean field shows that the change in the height field over the Northern Hemisphere is reflected in the enhancement of the negative phase of the NAO mode (which corresponds to a strong jet stream over the western Atlantic and a strong Icelandic low) and of the positive phase of the Pacific/North America (PNA) mode.

Modes of Interannual and Interdecadal Variability of Pacific SST

Abstract The multichannel singular spectrum analysis has been used to characterize the spatio–temporal structures of interdecadal and interannual variability of SST over the Pacific Ocean from 20°S to 58°N. Using the Comprehensive Ocean–Atmosphere Data Set from 1950 to 1993, three modes with distinctive spatio-temporal structures were found. They are an interdecadal mode, a quasi-quadrennial (QQ) oscillation with a period of 51 months, and a quasi-biennial (QB) oscillation with a period of 26 months. The interdecadal mode is a standing mode with opposite signs of SST anomalies in the North Pacific and in the tropical Pacific. The amplitude of this mode is larger in the central North Pacific than in the tropical Pacific. This mode contributes 11.4% to the total variance. It is associated with cooling in the central North Pacific and warming in the equatorial Pacific since around 1976–77. The QQ oscillation exhibits propagation of SST anomalies northeastward from the Philippine Sea and then eastward along 4...

The Nonlinear Patterns of North American Winter Temperature and Precipitation Associated with ENSO

Abstract Nonlinear projections of the tropical Pacific sea surface temperature anomalies (SSTAs) onto North American winter (November–March) surface air temperature (SAT) and precipitation anomalies have been performed using neural networks. During El Nino, the linear SAT response has positive anomalies centered over Alaska and western Canada opposing weaker negative anomalies centered over the southeastern United States. In contrast, the nonlinear SAT response, which is excited during both strong El Nino and strong La Nina, has negative anomalies centered over Alaska and northwestern Canada and positive anomalies over much of the United States and southern Canada. For precipitation, the linear response during El Nino has a positive anomaly area stretching from the east coast to the southwest coast of the United States and another positive area in northern Canada, in opposition to the negative anomaly area over much of southern Canada and northern United States, and another negative area over Alaska. In c...

The Enhanced PNA-Like Climate Response to Pacific Interannual and Decadal Variability

Abstract This study provides further evidence of the impacts of tropical Pacific interannual [El Nino–Southern Oscillation (ENSO)] and Northern Pacific decadal–interdecadal [North Pacific index (NPI)] variability on the Pacific–North American (PNA) sector. Both the tropospheric circulation and the North American temperature suggest an enhanced PNA-like climate response and impacts on North America when ENSO and NPI variability are out of phase. In association with this variability, large stationary wave activity fluxes appear in the mid- to high latitudes originating from the North Pacific and flowing downstream toward North America. Atmospheric heating anomalies associated with ENSO variability are confined to the Tropics, and generally have the same sign throughout the troposphere with maximum anomalies at 400 hPa. The heating anomalies that correspond to the NPI variability exhibit a center over the midlatitude North Pacific in which the heating changes sign with height, along with tropical anomalies o...

Impacts of Large-Scale Circulation Variability on Low Streamflows over Canada: A Review

Low streamflows constitute an important component of hydro-climatic extremes. This is particularly true for Canada where reduced flows can affect several economic and environmental activities ranging from less hydro-electric production and increased freshwater transportation costs, to reduced water quality and ecological habitat destruction. This paper reviews past research regarding the impacts of large-scale circulation patterns on streamflow variability (including low flows) over Canada. Results from the various studies reveal that streamflow responses are generally consistent with those observed for large-scale climate. For western Canada, this includes a higher frequency of low-flow events in association with the warmer/drier conditions during El Niño events and positive phases of the Pacific Decadal Oscillation (PDO) and the Pacific North American (PNA) pattern. Relationships in northern/northeastern regions of the country are less robust but in general, reduced streamflows occur during positive phases of the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO). However, it is clearly evident that the spatial and temporal aspects of these relationships are greatly influenced by hydro-climatic complexities associated with individual watersheds, especially in the cordilleran areas of Canada. Future research requires more in-depth analyses into the spatial and temporal aspects of relationships between circulation variability and low-flow occurrences over critical watersheds within Canada including the combination of climatic patterns and associations with regional, synoptic-scale circulation. The incorporation of fully coupled climate and hydrologic models to assess the impacts of projected climate change on future low-flow occurrences is also needed. This research would result in a better understanding and enhanced prediction of low streamflow events that is critical for the current and future efficient management of water resources throughout the country.