Seminar: Joowan Kim

Please join us tomorrow, Wednesday at 14:35 in Burnside 934 for a student seminar by Joowan Kim. Abstract is as follows:

 

Climatology of ERA-Interim and ensemble of CMIP5 models.

Annual-mean climatology (1979-2005) of 100-hPa temperature from a) ERA-Interim and b) ensemble of CMIP5 models. White contours denote OLR from observation and model ensemble respectively. c) Taylor diagram of the temperature field within 15S-15N for individual models (open and closed circles) and their ensemble (cross).

Thermal characteristics of the tropical tropopause layer in CMIP5 models: historical simulations

The climatology and variability of temperatures in the tropical tropopause layer are investigated in 16 Coupled Model Intercomparison Project Phase 5 (CMIP5) models for historical simulations. The climatology of 100-hPa temperatures compare well with ERA-Interim reanalysis. The models possess reasonable temperature minima in the deep tropics, but some models also have a warm bias or a bias in the location of the temperature minima. The CMIP5 models generally capture the phase of the seasonal cycle in 100-hPa temperatures, but the amplitude of the seasonal cycle varies greatly among models. The interannual variability in 100-hPa temperature is associated with the El Niño-Southern Oscillation (ENSO) and volcanic forcing in observation and CMIP5 models. Most of models successfully capture the ENSO-related large scale response, but the response to volcanic forcing is overestimated in many models. On intraseasonal timescales, observed and modeled variability is dominated by equatorial waves (Kelvin, inertio-gravity, and mixed Rossby-gravity waves) and the Madden-Julian Oscillation (MJO). Most models show variability related to the equatorial waves, but significant biases are found in the phase speeds of the waves when compared to ERA-Interim. The MJO signature is weak and non-distinguishable from the Kelvin wave power in most CMIP5 models.

Student Seminar: Amélie Bouchat

Energy dissipation in viscous-plastic sea ice models

Energy dissipation in viscous-plastic sea ice models

Energy dissipation in viscous-plastic sea ice models by Amélie Bouchat

Most current sea ice models are based on the viscous approximation introduced by Hibler (1979). These viscous-plastic (VP) models approximate the small elastic deformations by the viscous deformations of a creeping flow. The resulting numerical treatment is much more simple than in earlier sea ice models, but viscous deformations introduce a non-physical energy sink in the model since they are not reversible as the elastic deformations. The project is aimed at assessing the consequences, physically speaking, of this non-physical energy dissipation in the models and therefore verifying the validity of the VP approximation. The dissipation is studied using the kinetic energy balance that is derived using the continuity and momentum equations for sea ice. This analysis allows us to evaluate the different terms of the balance and look at the relative importance of the viscous dissipation. The results will be presented for a 40km-resolution run of 1 year. The dependence of the viscous dissipation on the number of Newton loops of the numerical solver of the momentum equation is also studied. Preliminary results at 20km-resolution will also be shown.

Student Seminar: Melissa Gervais

Please join us tomorrow in Burnside 934 at 14:35 for a student seminar by Melissa Gervais. Abstract follows.

How Well is the Distribution of Precipitation Represented? Part I: Impacts of Station Density and Resolution Changes on Gridded Station Data

Precipitation is one of the most important variables to predict in future climate change owing to the socio-economic implications for water resources. However, it has historically been a very challenging variable for climate models to predict. Newer versions of Community Climate System Model (CCSM) from the National Center for Atmospheric Research (NCAR) have seen great improvements in their representation of the distribution of precipitation, with results now very close to observations (Gent 2011). The accuracy of precipitation observations used to validate the GCM output is thus becoming increasingly important. Results will be presented from the first of two studies on examining the ability of observations, reanalysis, the CCSM4 fully coupled model, and the NCAR Community Atmosphere Model (CAM5), to represent the distribution of precipitation. Here, we focus on the accuracy of interpolating station data in terms of the method of interpolation and the station density.

Station data from the Global Historical Climatology Network – Daily Version 1.0, within the United States, will be used to create and test gridded precipitation products. The goal is firstly to examine what the impact of gridding station data is on the precipitation statistics and whether the gridding method used is important. Secondly, an experiment will be conducted to determine how dense an observation network needs to be, in different climatic regions, in order to produce an accurate distribution of precipitation. This allows us to identify regions where station density is not high enough to trust the gridded precipitation data for validating GCMs.

Student Seminar: Hossein Amini Kafiabad

Lagrangian Detection of Aerial Turbulence for Landing Aircraft

Our very own Hossein Amini Kafiabad will be presenting a talk on “Lagrangian Detection of Aerial Turbulence for Landing Aircraft” on Wednesday September 26 at 2:35pm in Burnside 934. His abstract follows:

Recent studies have shown that aerial disturbances affecting landing  aircraft have a coherent  signature in the Lagrangian aerial particle dynamics inferred from  ground-based lidar scans. Specifically, attracting Lagrangian Coherent Structures (LCSs) mark the intersection of localized material upwelling with the cone of the lidar scan. Here we test the detection power of LCSs on historical landing data and corresponding pilot reports of disturbances from Hong Kong International Airport. We find that a specific LCS indicator, the gradient of the Finite-Time Lyapunov Exponent (FTLE) field along the landing path, is a highly efficient marker of turbulent upwellings. In particular, projected FTLE gradients closely approach the efficiency of the wind-shear alert system currently in operation at the airport, even though the latter system relies on multiple sources of data beyond those used in this study. This shows significant potential for the operational use of FTLE gradients in the real-time detection of aerial turbulence over airports.

Blog authors are solely responsible for the content of the blogs listed in the directory. Neither the content of these blogs, nor the links to other web sites, are screened, approved, reviewed or endorsed by McGill University. The text and other material on these blogs are the opinion of the specific author and are not statements of advice, opinion, or information of McGill.