Bohdan Kochtubajda


2020

DOI bib
Near-0 °C surface temperature and precipitation type patterns across Canada
Éva Mekis, Ronald E. Stewart, Julie M. Thériault, Bohdan Kochtubajda, Barrie Bonsal, Zhuo Liu
Hydrology and Earth System Sciences, Volume 24, Issue 4

Abstract. The 0 ∘C temperature threshold is critical for many meteorological and hydrological processes driven by melting and freezing in the atmosphere, surface, and sub-surface and by the associated precipitation varying between rain, freezing rain, wet snow, and snow. This threshold is especially important in cold regions such as Canada, because it is linked with freeze–thaw, snowmelt, and permafrost. This study develops a Canada-wide perspective on near-0 ∘C conditions using hourly surface temperature and precipitation type observations from 92 climate stations for the period from 1981 to 2011. In addition, nine stations from various climatic regions are selected for further analysis. Near-0 ∘C conditions are defined as periods when the surface temperature is between −2 and 2 ∘C. Near-0 ∘C conditions occur often across all regions of the country, although the annual number of days and hours and the duration of these events varies dramatically. Various types of precipitation (e.g., rain, freezing rain, wet snow, and ice pellets) sometimes occur with these temperatures. Near-0 ∘C conditions and the reported precipitation type occurrences tend to be higher in Atlantic Canada, although high values also occur in other regions. Trends of most temperature-based and precipitation-based indicators show little or no change despite a systematic warming in annual surface temperatures over Canada. Over the annual cycle, near-0 ∘C temperatures and precipitation often exhibit a pattern: short durations occur around summer, driven by the diurnal cycle, and a tendency toward longer durations around winter, associated with storms. There is also a tendency for near-0 ∘C surface temperatures to occur more often than expected relative to other temperature windows at some stations due, at least in part, to diabatic cooling and heating that take place with melting and freezing, respectively, in the atmosphere and at the surface.

2019

DOI bib
A Review and Synthesis of Future Earth System Change in theInterior of Western Canada: Part I – Climate and Meteorology
Ronald E. Stewart, Kit K. Szeto, Barrie Bonsal, John Hanesiak, Bohdan Kochtubajda, Yanping Li, Julie M. Thériault, C. M. DeBeer, Benita Y. Tam, Zhenhua Li, Lu Zhuo, Jennifer Bruneau, Sébastien Marinier, Dominic Matte

Abstract. The Interior of Western Canada, up to and including the Arctic, has experienced rapid change in its climate, hydrology, cryosphere and ecosystems and this is expected to continue. Although there is general consensus that warming will occur in the future, many critical issues remain. In this first of two articles, attention is placed on atmospheric-related issues that range from large scales down to individual precipitation events. Each of these is considered in terms of expected change organized by season and utilizing climate scenario information as well as thermodynamically-driven future climatic forcing simulations. Large scale atmospheric circulations affecting this region are generally projected to become stronger in each season and, coupled with warming temperatures, lead to enhancements of numerous water-related and temperature-related extremes. These include winter snowstorms, freezing rain, drought as well as atmospheric forcing of spring floods although not necessarily summer convection. Collective insights of these atmospheric findings are summarized in a consistent, connected physical framework.

DOI bib
Assessment of Near 0 °C Temperature and Precipitation Characteristicsacross Canada
Éva Mekis, Ronald E. Stewart, Julie M. Thériault, Bohdan Kochtubajda, Barrie Bonsal, Zhuo Liu

Abstract. The 0 °C temperature threshold is critical to many meteorological and hydrological processes driven by melting and freezing in the atmosphere, surface and sub-surface and by the associated precipitation varying between rain, freezing rain, wet snow and snow. This threshold, linked with freeze-thaw, is especially important in cold regions such as Canada. This study develops a Canada-wide perspective on near 0 °C conditions with a particular focus on the occurrence of its associated precipitation. Since this analysis requires hourly values of surface temperature and precipitation type observations, it was limited to 92 stations over the 1981–2011 period. In addition, nine stations representative of various climatic regions are selected for further analysis. Near 0 °C conditions are defined as periods when the surface temperature is between −2 °C and 2 °C. Near 0 °C conditions occur often across all regions of the country although the annual number of days and hours and the duration of these events varies dramatically. Various forms of precipitation (including rain, freezing rain, wet snow and ice pellets) are sometimes linked with these temperatures with highest fractions tending to occur in Atlantic Canada. Trends of most temperature-based and precipitation-based indicators show little or no change despite a systematic warming in annual temperatures. Over the annual cycle, near 0 °C temperatures and precipitation often exhibit a pattern with short durations near summer driven by the diurnal cycle, while longer durations tend to occur more towards winter associated with storms. There is also a tendency for near 0 °C temperatures to occur more often than expected relative to other temperature windows; due at least in part to diabatic cooling and heating occurring with melting and freezing, respectively, in the atmosphere and at the surface.

DOI bib
An Assessment of Surface and Atmospheric Conditions Associated with the Extreme 2014 Wildfire Season in Canada’s Northwest Territories
Bohdan Kochtubajda, Ronald E. Stewart, Mike D. Flannigan, Barrie Bonsal, Charles Cuell, Curtis Mooney
Atmosphere-Ocean, Volume 57, Issue 1

Weather and climate are major factors influencing worldwide wildfire activity. This study assesses surface and atmospheric conditions associated with the 2014 extreme wildfires in the Northwest Ter...

DOI bib
Summary and synthesis of Changing Cold Regions Network (CCRN) research in the interior of western Canada – Part 1: Projected climate and meteorology
Ronald E. Stewart, Kit K. Szeto, Barrie Bonsal, John Hanesiak, Bohdan Kochtubajda, Yanping Li, Julie M. Thériault, C. M. DeBeer, Benita Y. Tam, Zhenhua Li, Zhuo Liu, Jennifer Bruneau, Patrick Duplessis, Sébastien Marinier, Dominic Matte
Hydrology and Earth System Sciences, Volume 23, Issue 8

Abstract. The interior of western Canada, up to and including the Arctic, has experienced rapid change in its climate, hydrology, cryosphere, and ecosystems, and this is expected to continue. Although there is general consensus that warming will occur in the future, many critical issues remain. In this first of two articles, attention is placed on atmospheric-related issues that range from large scales down to individual precipitation events. Each of these is considered in terms of expected change organized by season and utilizing mainly “business-as-usual” climate scenario information. Large-scale atmospheric circulations affecting this region are projected to shift differently in each season, with conditions that are conducive to the development of hydroclimate extremes in the domain becoming substantially more intense and frequent after the mid-century. When coupled with warming temperatures, changes in the large-scale atmospheric drivers lead to enhancements of numerous water-related and temperature-related extremes. These include winter snowstorms, freezing rain, drought, forest fires, as well as atmospheric forcing of spring floods, although not necessarily summer convection. Collective insights of these atmospheric findings are summarized in a consistent, connected physical framework.

2017

DOI bib
Characteristics, atmospheric drivers and occurrence patterns of freezing precipitation and ice pellets over the Prairie Provinces and Arctic Territories of Canada: 1964–2005
Bohdan Kochtubajda, Curtis Mooney, Ronald E. Stewart
Atmospheric Research, Volume 191

Abstract Freezing precipitation and ice pellet events on the Canadian Prairies and Arctic territories of Canada often lead to major disruptions to air and ground transportation, damage power grids and prevent arctic caribou and other animals from accessing the plants and lichen they depend on for survival. In a warming climate, these hazards and associated impacts will continue to happen, although their spatial and temporal characteristics may vary. In order to address these issues, the occurrence of freezing rain, freezing drizzle, and ice pellets from 1964 to 2005 is examined using hourly weather observations at 27 manned 24 h weather stations across the different climatic regions of the Prairie Provinces and Arctic Territories of Canada. Because of the enormous size of the area and its diverse climatic regions, many temporal and spatial differences in freezing precipitation and ice pellet characteristics occur. The 12 most widespread freezing rain events over the study area are associated with only two atmospheric patterns with one linked to strong warm advection between low and high pressure centres and the other pattern associated with chinooks occurring east of the Rocky Mountains. Given the annual patterns of freezing rain occurrence found in this study, it is proposed that a maximum of five regimes exist and three occur within the Prairies and Arctic.

DOI bib
A Numerical Study of the June 2013 Flood-Producing Extreme Rainstorm over Southern Alberta
Yanping Li, Kit K. Szeto, Ronald E. Stewart, Julie M. Thériault, Liang Chen, Bohdan Kochtubajda, Anthony Liu, Sudesh Boodoo, Ron Goodson, Curtis Mooney, Sopan Kurkute, Yanping Li, Kit K. Szeto, Ronald E. Stewart, Julie M. Thériault, Liang Chen, Bohdan Kochtubajda, Anthony Liu, Sudesh Boodoo, Ron Goodson, Curtis Mooney, Sopan Kurkute
Journal of Hydrometeorology, Volume 18, Issue 8

Abstract A devastating, flood-producing rainstorm occurred over southern Alberta, Canada, from 19 to 22 June 2013. The long-lived, heavy rainfall event was a result of complex interplays between topographic, synoptic, and convective processes that rendered an accurate simulation of this event a challenging task. In this study, the Weather Research and Forecasting (WRF) Model was used to simulate this event and was validated against several observation datasets. Both the timing and location of the model precipitation agree closely with the observations, indicating that the WRF Model is capable of reproducing this type of severe event. Sensitivity tests with different microphysics schemes were conducted and evaluated using equitable threat and bias frequency scores. The WRF double-moment 6-class microphysics scheme (WDM6) generally performed better when compared with other schemes. The application of a conventional convective/stratiform separation algorithm shows that convective activity was dominant during the early stages, then evolved into predominantly stratiform precipitation later in the event. The HYSPLIT back-trajectory analysis and regional water budget assessments using WRF simulation output suggest that the moisture for the precipitation was mainly from recycling antecedent soil moisture through evaporation and evapotranspiration over the Canadian Prairies and the U.S. Great Plains. This analysis also shows that a small fraction of the moisture can be traced back to the northeastern Pacific, and direct uptake from the Gulf of Mexico was not a significant source in this event.

DOI bib
A Numerical Study of the June 2013 Flood-Producing Extreme Rainstorm over Southern Alberta
Yanping Li, Kit K. Szeto, Ronald E. Stewart, Julie M. Thériault, Liang Chen, Bohdan Kochtubajda, Anthony Liu, Sudesh Boodoo, Ron Goodson, Curtis Mooney, Sopan Kurkute, Yanping Li, Kit K. Szeto, Ronald E. Stewart, Julie M. Thériault, Liang Chen, Bohdan Kochtubajda, Anthony Liu, Sudesh Boodoo, Ron Goodson, Curtis Mooney, Sopan Kurkute
Journal of Hydrometeorology, Volume 18, Issue 8

Abstract A devastating, flood-producing rainstorm occurred over southern Alberta, Canada, from 19 to 22 June 2013. The long-lived, heavy rainfall event was a result of complex interplays between topographic, synoptic, and convective processes that rendered an accurate simulation of this event a challenging task. In this study, the Weather Research and Forecasting (WRF) Model was used to simulate this event and was validated against several observation datasets. Both the timing and location of the model precipitation agree closely with the observations, indicating that the WRF Model is capable of reproducing this type of severe event. Sensitivity tests with different microphysics schemes were conducted and evaluated using equitable threat and bias frequency scores. The WRF double-moment 6-class microphysics scheme (WDM6) generally performed better when compared with other schemes. The application of a conventional convective/stratiform separation algorithm shows that convective activity was dominant during the early stages, then evolved into predominantly stratiform precipitation later in the event. The HYSPLIT back-trajectory analysis and regional water budget assessments using WRF simulation output suggest that the moisture for the precipitation was mainly from recycling antecedent soil moisture through evaporation and evapotranspiration over the Canadian Prairies and the U.S. Great Plains. This analysis also shows that a small fraction of the moisture can be traced back to the northeastern Pacific, and direct uptake from the Gulf of Mexico was not a significant source in this event.

2016

DOI bib
The June 2013 Alberta Catastrophic Flooding Event: Part 1-Climatological aspects and hydrometeorological features
Anling Liu, Curtis Mooney, Kit K. Szeto, Julie M. Thériault, Bohdan Kochtubajda, Ronald E. Stewart, Sudesh Boodoo, Ron Goodson, Yanping Li, John W. Pomeroy
Hydrological Processes, Volume 30, Issue 26

In June 2013, excessive rainfall associated with an intense weather system triggered severe flooding in southern Alberta, which became the costliest natural disaster in Canadian history. This article provides an overview of the climatological aspects and large-scale hydrometeorological features associated with the flooding event based upon information from a variety of sources, including satellite data, upper air soundings, surface observations and operational model analyses. The results show that multiple factors combined to create this unusually severe event. The event was characterized by a slow-moving upper level low pressure system west of Alberta, blocked by an upper level ridge, while an associated well-organized surface low pressure system kept southern Alberta, especially the eastern slopes of the Rocky Mountains, in continuous precipitation for up to two days. Results from air parcel trajectory analysis show that a significant amount of the moisture originated from the central Great Plains, transported into Alberta by a southeasterly low level jet. The event was first dominated by significant thunderstorm activity, and then evolved into continuous precipitation supported by the synoptic-scale low pressure system. Both the thunderstorm activity and upslope winds associated with the low pressure system produced large rainfall amounts. A comparison with previous similar events occurring in the same region suggests that the synoptic-scale features associated with the 2013 rainfall event were not particularly intense; however, its storm environment was the most convectively unstable. The system also exhibited a relatively high freezing level, which resulted in rain, rather than snow, mainly falling over the still snow-covered mountainous areas. Melting associated with this rain-on-snow scenario likely contributed to downstream flooding. Furthermore, above-normal snowfall in the preceding spring helped to maintain snow in the high-elevation areas, which facilitated the rain-on-snow event.