1.0 INTRODUCTION: Wind, Insects & Complex Terrain The mountain pine beetle population in British Columbia has been increasing over the past decade and has reached epidemic levels (affecting a further 4.2 million hectares of forest in 2002). During outbreaks, populations exist at the landscape level as a result of local population growth, and both within-stand movements and above canopy transport. This multi-phase project is concerned exclusively with wind-borne transport above the canopy. The aim is to assess the role of the atmosphere, and its interaction with complex terrain, in describing landscape level movements of the mountain pine beetle. The nature of this interaction is highly dependant upon the synoptic conditions that exist during the emergence and flight window. The purpose of the current work is to identify the large-scale background weather conditions, that exist during periods of peak emergence. 2.0 BACKGROUND: Mountain Pine Beetle Biology The mountain pine beetle is a univoltine species that kills its host in the process of breeding and undertakes a single flight each generation. Mating occurs after flight beneath the bark, and eggs are deposited on either side of a main gallery. Larvae hatch in 7-10 days and mine separate feeding tunnels. Larvae over-winter under the bark and continue to feed in spring. Fully grown larvae hollow out a pupal cell at the end of the tunnel and pupate. New adults bore individual exit holes in the bark and emerge to locate new hosts, repeating the life cycle. Movements may be short (~1 km), medium (~10 km) or long range (~100 km). Short-range movements dominate, and occur under the canopy in relation to various host tree, stand and site characteristics, as well as behaviour modifying chemicals. Convection, which predominates during the emergence and flight period, is thought to carry some beetles above the forest canopy to be passively transported over longer distances. 3.0 METHOD: Composite Classification & Peak Emergence Criteria 2.1 MPB Life Cycle 2.2 Patterns of Emergence Populations have a strong requirement to mature and emerge simultaneously (synchrony), and at an appropriate time of year (seasonality). Seasonality is required to avoid lethal cold temperatures during the flight period, and to achieve full ovipositional potential before lethal fall/winter temperatures. Synchrony is required for a successful mass attack strategy. Logan and Bentz (1999) have concluded that direct temperature control alone is sufficient for maintaining seasonality. Emergence typically occurs between mid-July and mid-August and proceeds slowly at first, followed by a period of rapid emergence over 7-10 days when approximately 50% of the total population emerges (McCambridge, 1964). Emergence begins when ambient temperatures reach about 16°C, and increases with temperature up to about 30°C, above which both hourly and daily rates begin to decline. During the period of rapid emergence, there are often two distinct periods of increasing daily temperature, or heating cycles, each with individual emergence maxima. Emergence tends to peak when the average daily temperature is higher than 20°C for at least three consecutive days (Safranyik and Linton, 1993). Optimal conditions for mass attack occur when the daily maximum temperature remains between 25 °C to 30°C (Gray et al., 1972). Under such conditions, peak emergence occurs between 11:00 am and 2:00 pm. A synoptic composite is a climatology based on events, and are typically average pressure maps of specific situations. The compositing of a large number of cases into one dataset can identify processes common to most events. In the absence of sufficient historical emergence data, temperature was used as an environmental surrogate for emergence activity. The criteria for identifying potential periods of peak emergences was a daily maximum temperature that remained within the optimal temperature range (25-30 ° C) for more than 4 consecutive days. A total of 71 heating cycles were identified, and on average, were 5 days in length. Daily maximum temperature data for the period were obtained from the Environment Canada station at the Prince George Airport (YXS). Gridded pressure fields for the period were obtain from model output of the NCEP/NCAR Reanalysis Project (Kalnay et al., 1996). Composites were constructed by averaging daily mean reanalysis fields corresponding to day 3 of each of the identified heating cycles falling in July, or August. HEATING CYCLE PROPERTIES NCEP REANALYSIS GRID RESOLUTION OVER BC and LOCATION OF PRINCE GEORGE AIRPORT (YXS) SCEMATIC REPRESENTATIONS of TYPICAL EMERGENCE TRENDS DOCUMENTED IN THE LITERATURE