Polar MM5 Simulations of the Winter Climate of the Laurentide Ice Sheet at the LGM

Optimized regional climate simulations are conducted using the Polar MM5, a version of the fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5), with a 60-km horizontal resolution domain over North America during the Last Glacial Maximum (LGM, 21 000 calendar years ago), when much of the continent was covered by the Laurentide Ice Sheet (LIS). The objective is to describe the LGM annual cycle at high spatial resolution with an emphasis on the winter atmospheric circulation. Output from a tailored NCAR Community Climate Model version 3 (CCM3) simulation of the LGM climate is used to provide the initial and lateral boundary conditions for Polar MM5. LGM boundary conditions include continental ice sheets, appropriate orbital forcing, reduced CO2 concentration, paleovegetation, modified sea surface temperatures, and lowered sea level. Polar MM5 produces a substantially different atmospheric response to the LGM boundary conditions than CCM3 and other recent GCM simulations. In particular, from November to April the upper-level flow is split around a blocking anticyclone over the LIS, with a northern branch over the Canadian Arctic and a southern branch impacting southern North America. The split flow pattern is most pronounced in January and transitions into a single, consolidated jet stream that migrates northward over the LIS during summer. Sensitivity experiments indicate that the winter split flow in Polar MM5 is primarily due to mechanical forcing by LIS, although model physics and resolution also contribute to the simulated flow configuration. Polar MM5 LGM results are generally consistent with proxy climate estimates in the western United States, Alaska, and the Canadian Arctic and may help resolve some long-standing discrepancies between proxy data and previous simulations of the LGM climate.

Peer Acceptance and Friendship as Predictors of Early Adolescents' Adjustment Across the Middle School Transition

This study examines several aspects of adolescents' pretransition peer relationships as predictors of their adjustment to middle school. Participants were 365 students (175 boys; 99% Caucasian) involved in the Time 1 (the spring of fifth grade) and Time 2 (the fall of sixth grade) assessments. Adolescents completed measures that assessed peer acceptance, number of friends, the quality of a specific mutual friendship, loneliness, depression, self-esteem, and involvement in school. Academic achievement and absentee data were obtained from student files. Regression analyses indicated that the pretransition peer variables predicted posttransition loneliness, self-esteem, school involvement, and academic achievement. The patterns of prediction varied slightly for each adjustment variable, with the most robust relationship being between peer acceptance and achievement. Results of repeated-measures MANOVAs indicated no differential changes in adjustment across time by gender. Implications for including a peer component in programs that prepare students for the middle school transition are discussed.