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This paper surveys the current state of knowledge regarding large-scale meteorological patterns (LSMPs) associated with short-duration (less than 1 week) extreme precipitation events over North America. In contrast to teleconnections, which are typically defined based on the characteristic spatial variations of a meteorological field or on the remote circulation response to a known forcing, LSMPs are defined relative to the occurrence of a specific phenomenon—here, extreme precipitation—and with an emphasis on the synoptic scales that have a primary influence in individual events, have medium-range weather predictability, and are well-resolved in both weather and climate models. For the LSMP relationship with extreme precipitation, we consider the previous literature with respect to definitions and data, dynamical mechanisms, model representation, and climate change trends. There is considerable uncertainty in identifying extremes based on existing observational precipitation data and some limitations in analyzing the associated LSMPs in reanalysis data. Many different definitions of “extreme” are in use, making it difficult to directly compare different studies. Dynamically, several types of meteorological systems—extratropical cyclones, tropical cyclones, mesoscale convective systems, and mesohighs—and several mechanisms—fronts, atmospheric rivers, and orographic ascent—have been shown to be important aspects of extreme precipitation LSMPs. The extreme precipitation is often realized through mesoscale processes organized, enhanced, or triggered by the LSMP. Understanding of model representation, trends, and projections for LSMPs is at an early stage, although some promising analysis techniques have been identified and the LSMP perspective is useful for evaluating the model dynamics associated with extremes.

Temperature and water vapor profiles are essential to climate change studies and weather forecasting. Hyperspectral instruments are of great value for retrieving temperature and water vapor profiles, enabling accurate monitoring of their changes. Successful retrievals of temperature and water vapor profiles require accuracy of hyperspectral radiometer measurements. In this study, the radiometric accuracy of an airborne hyperspectral microwave radiometer, the High Spectral Resolution Airborne Microwave Sounder (HiSRAMS), and a ground-based hyperspectral infrared radiometer, the Atmospheric Emitted Radiance Interferometer (AERI), is simultaneously assessed by performing radiative closure tests under clear-sky conditions in Ottawa, Canada. As an airborne instrument, HiSRAMS has two radiometers measuring radiance in the oxygen band (49.6–58.3 GHz) and water vapor band (175.9–184.6 GHz) for zenith-pointing and nadir-pointing observations. AERI provides ground-based, zenith-pointing radiance measurements between 520 and 1800 cm -1. A systematic warm radiance bias is present in AERI observations in the window band. Upon removal of this bias, improved radiative closure was attained in the window band. The brightness temperature (BT) bias in nadir-pointing HiSRAMS observations is smaller than at the zenith. A novel but straightforward method is developed to diagnose the radiometric accuracy of the two instruments in comparison based on the relationship between radiometric bias and optical depth. Compared to AERI, HiSRAMS demonstrates similar radiometric accuracy for nadir-pointing measurements but exhibits relatively poor accuracy for zenith-pointing measurements, which requires further characterization. Future work on temperature and water vapor concentration retrievals using HiSRAMS and AERI is warranted. [ABSTRACT FROM AUTHOR]

The objective of this paper is to review statistical methods, dynamics, modeling efforts, and trends related to temperature extremes, with a focus upon extreme events of short duration that affect parts of North America. These events are associated with large scale meteorological patterns (LSMPs). The statistics, dynamics, and modeling sections of this paper are written to be autonomous and so can be read separately. Methods to define extreme events statistics and to identify and connect LSMPs to extreme temperature events are presented. Recent advances in statistical techniques connect LSMPs to extreme temperatures through appropriately defined covariates that supplement more straightforward analyses. Various LSMPs, ranging from synoptic to planetary scale structures, are associated with extreme temperature events. Current knowledge about the synoptics and the dynamical mechanisms leading to the associated LSMPs is incomplete. Systematic studies of: the physics of LSMP life cycles, comprehensive model assessment of LSMP-extreme temperature event linkages, and LSMP properties are needed. Generally, climate models capture observed properties of heat waves and cold air outbreaks with some fidelity. However they overestimate warm wave frequency and underestimate cold air outbreak frequency, and underestimate the collective influence of low-frequency modes on temperature extremes. Modeling studies have identified the impact of large-scale circulation anomalies and land–atmosphere interactions on changes in extreme temperatures. However, few studies have examined changes in LSMPs to more specifically understand the role of LSMPs on past and future extreme temperature changes. Even though LSMPs are resolvable by global and regional climate models, they are not necessarily well simulated. The paper concludes with unresolved issues and research questions.

Temperature and water vapor profiles are essential to climate change studies and weather forecasting. Hyperspectral instruments are of great value for retrieving temperature and water vapor profiles, enabling accurate monitoring of their changes. Successful retrievals of temperature and water vapor profiles require hyperspectral radiometer measurement accuracy. In this study, the radiometric accuracy of an airborne hyperspectral microwave radiometer, High Spectral Resolution Airborne Microwave Sounder (HiSRAMS), and a ground-based hyperspectral infrared radiometer, Atmospheric Emitted Radiance Interferometer (AERI), is simultaneously assessed by performing radiative closure tests under clear-sky conditions. As an airborne instrument, HiSRAMS has two radiometers measuring radiance in the oxygen band (49.6-58.3 GHz) and water vapor band (175.9-184.6 GHz) for zenith-pointing and nadir-pointing observations. AERI provides ground-based, zenithpointing radiance measurements between 520 and 1800 cm-1 . A systematic warm radiance bias is present in the temperaturesensitive channels in AERI observations in the window band. Upon removal of this bias, improved radiative closure was attained in the window band. The brightness temperature (BT) bias in nadir-pointing HiSRAMS observations is smaller than at the zenith. A novel but straightforward method is developed to diagnose the radiometric accuracy of the two instruments in comparison based on the relationship between radiometric bias and optical depth. Compared to AERI, HiSRAMS demonstrates similar radiometric accuracy for nadir-pointing measurements but exhibits relatively poor accuracy for zenith-pointing measurements, which requires further characterization. Future work on temperature and water vapor concentration retrievals using HiSRAMS and AERI is warranted. [ABSTRACT FROM AUTHOR]

The Tenth Cyclone Workshop was held at the Far Hills Inn and Conference Centre in Val Morin, Quebec, Canada, 22-26 September 1997. The workshop highlights included a tribute to the scientific contributions of Chester Newton, Richard Reed, and Frederick Sanders. A total of 68 contributed and invited talks, along with evening sessions on the historical development of scientific ideas, the utility of ensemble forecasting, satellite-derived datasets and their impact on research, and a long-term potential-vorticity perspective, constituted the workshop schedule.

The first COMPARE (Comparison of Mesoscale Prediction and Research Experiments) workshop was held in Montreal, Quebec, Canada, from 3 to 5 October 1994 and was cosponsored by Environment Canada and the World Meteorological Organization. The COMPARE project is an international mesoscale modeling intercomparison effort that aims to propose and perform mesoscale model and data assimilation intercomparison experiments, to identify important issues of mesoscale research and prediction that may be addressed by numerical experimentation, and to gradually establish a test bed of interesting and challenging mesoscale cases. The workshop objectives were to discuss the results of the first case, to complete the planning for the second case, and to discuss possible future cases and activities. The first case is a typical explosive marine cyclogenesis event drawn from the concurrent Canadian Atlantic Storms Program and the Genesis of Atlantic Lows Experiment. Twelve groups from seven countries performed a controlled set of horizontal and vertical resolution experiments using the provided reanalyses. The resulting forecasts were objectively verified, and an evaluation study was undertaken. Each participating group summarized its results, and preliminary conclusions from the evaluation study were presented and discussed. Most models tended to underestimate the deepening of the secondary low and to position it too far westward. Forecasts generally improved with horizontal resolution but were relatively insensitive to higher vertical resolution. The upper-level dynamics are important at the initiation of the storm, whereas surface fluxes contribute significantly to its later intensification. Follow-up work on the first case includes further experimentation and publication of an in-depth evaluation paper. The second case is drawn from the Pyrenees Experiment, a field experiment to better understand, model, and predict mountain wave phenomena. A 'straw man' experimental design was proposed and refined, and a detailed document is now available. A workshop will be held in Toulouse, France, to discuss the results of participating groups. Several other possible cases and activities were also presented and discussed. A case drawn from Tropical Cyclone Motion 1990, a field experiment to improve the basic understanding of tropical cyclone motion in the western North Pacific, is the most promising candidate for the third case. The envisaged time frame would lead to a workshop in 1997. A proposal was also made for a large-scale westerly wind burst case drawn from the Tropical Ocean Global Atmosphere-Coupled Ocean Atmosphere Response Experiment, but a sponsoring center remains to be identified. A FASTEX (Fronts and Atlantic Storm Tracks Experiment) case would be a prime candidate for a future mesoscale data assimilation and forecast intercomparison. FASTEX is a planned field experiment to understand end-of-storm-track cyclogenesis, the role of midlatitude storm-track cloud systems within the climate system, and stratosphere-troposphere exchange in tropopause folds. A further possible activity would be a short-range mesoscale ensemble forecast intercomparison.

As subsaturated air ascends sloping isentropic surfaces, adiabatic expansion results in cooling and relative moistening. This process is an effective way to precondition the atmosphere for efficient moist processes while bringing parcels to saturation, and thereafter acts to maintain saturation during condensation. The goal of this study is to develop a diagnostic quantity that highlights circulations and regions in which the process of parcel moistening by isentropic ascent is active. Among the many features that rely on this process for the generation of an important fraction of their energy are oceanic cyclones, transitioning tropical cyclones, warm conveyor belts, diabatic Rossby vortices, and predecessor rain events. The baroclinic moisture flux (BMF) is defined as moisture transport by the component of vertical motion associated with isentropic upgliding. In warm conveyor belt and diabatic Rossby vortex case studies, the BMF appears to be successful in identifying the portion of the circulation in which this process is actively bringing parcels to saturation to promote the formation of clouds and precipitation. On a broader scale, the climatological maxima of the BMF highlight regions in which parcel moistening by isentropic ascent is anticipated to have a nonnegligible impact on the atmospheric state either through the action of the mean flow or via the repeated occurrence of isolated large-BMF events. The process-centric foundation of the BMF makes it useful as a filtering or exploratory variable, with the potential for extension into predictive applications. [ABSTRACT FROM AUTHOR]