Robert Tardif - Academia.edu (original) (raw)

Papers by Robert Tardif

Atmosphere

Accurate and timely fog forecasts are needed to support decision making for various activities wh... more Accurate and timely fog forecasts are needed to support decision making for various activities which are critically affected by low visibility conditions [...]

Although Atlantic hurricane risk is expected to increase in a warming climate, projecting trends ... more Although Atlantic hurricane risk is expected to increase in a warming climate, projecting trends in hurricane frequency over the present century is still highly uncertain. The short instrumental record limits our understanding of hurricane activity and its relationship to climate, especially on multi-decadal and longer time scales. Here we extend the instrumental hurricane frequency record using two independent sources of information: (1) a reconstruction of basin-wide Atlantic hurricane frequency over the last millennium, developed from sedimentary paleohurricane records; (2) a statistical model of hurricane activity using sea surface temperatures (SSTs) from the Last Millennium Reanalysis (LMR) datasets. We find statistically significant agreement between the two estimates, suggesting that a robust climate signal of hurricane frequency over the past millennium can be captured from proxy data. Neither estimate of hurricane frequency indicates that the late 20th century hurricane fr...

Journal of Climate, 2021

In the past 40 years, the global annual mean surface temperature has experienced a nonuniform war... more In the past 40 years, the global annual mean surface temperature has experienced a nonuniform warming, differing from the spatially uniform warming simulated by the forced responses of large multimodel ensembles to anthropogenic forcing. Rather, it exhibits significant asymmetry between the Arctic and Antarctic, with intermittent and spatially varying warming trends along the Northern Hemisphere (NH) midlatitudes and a slight cooling in the tropical eastern Pacific. In particular, this “wavy” pattern of temperature changes over the NH midlatitudes features strong cooling over Eurasia in boreal winter. Here, we show that these nonuniform features of surface temperature changes are likely tied together by tropical eastern Pacific sea surface temperatures (SSTs), via a global atmospheric teleconnection. Using six reanalyses, we find that this teleconnection can be consistently obtained as a leading circulation mode in the past century. This tropically driven teleconnection is associate...

Monthly Weather Review, 2020

A sensitivity analysis methodology recently developed by the authors is applied to COAMPS and WRF... more A sensitivity analysis methodology recently developed by the authors is applied to COAMPS and WRF. The method involves varying model parameters according to Latin Hypercube Sampling, and developing multivariate multiple regression models that map the model parameters to forecasts over a spatial domain. The regression coefficients and p values testing whether the coefficients are zero serve as measures of sensitivity of forecasts with respect to model parameters. Nine model parameters are selected from COAMPS and WRF, and their impact is examined on nine forecast quantities (water vapor, convective and gridscale precipitation, and air temperature and wind speed at three altitudes). Although the conclusions depend on the model parameters and specific forecast quantities, it is shown that sensitivity to model parameters is often accompanied by nontrivial spatial structure, which itself depends on the underlying forecast model (i.e., COAMPS vs WRF). One specific difference between these...

Climate of the Past, 2018

Monthly Weather Review, 2018

A methodology is proposed for examining the effect of model parameters (assumed to be continuous)... more A methodology is proposed for examining the effect of model parameters (assumed to be continuous) on the spatial structure of forecasts. The methodology involves several statistical methods of sampling and inference to assure the sensitivity results are statistically sound. Specifically, Latin hypercube sampling is employed to vary the model parameters, and multivariate multiple regression is used to account for spatial correlations in assessing the sensitivities. The end product is a geographic “map” of p values for each model parameter, allowing one to display and examine the spatial structure of the sensitivity. As an illustration, the effect of 11 model parameters in a mesoscale model on forecasts of convective and grid-scale precipitation, surface air temperature, and water vapor is studied. A number of spatial patterns in sensitivity are found. For example, a parameter that controls the fraction of available convective clouds and precipitation fed back to the grid scale influe...

Climate of the Past Discussions, 2018

Meteorological Applications, 2018

Stochastic kinetic energy backscatter schemes (SKEBSs) are introduced in numerical weather foreca... more Stochastic kinetic energy backscatter schemes (SKEBSs) are introduced in numerical weather forecast models to represent uncertainties related to unresolved subgrid‐scale processes. These schemes are formulated using a set of parameters that must be determined using physical knowledge and/or to obtain a desired outcome. Here, a methodology is developed for assessing the effect of four factors on spatial features of forecasts simulated by the SKEBS‐enabled Weather Research and Forecasting model. The four factors include two physically motivated SKEBS parameters (the determining amplitude of perturbations applied to stream function and potential temperature tendencies), a purely stochastic element (a seed used in generating random perturbations) and a factor reflecting daily variability. A simple threshold‐based approach for identifying coherent objects within forecast fields is employed, and the effect of the four factors on object features (e.g. number, size and intensity) is assesse...

Climate of the Past Discussions, 2017

The Last Millennial Reanalysis (LMR) employs a data assimilation approach to reconstruct climate ... more The Last Millennial Reanalysis (LMR) employs a data assimilation approach to reconstruct climate fields from annually-resolved proxy data over years 0–2000CE. We use the LMR to examine Atlantic Multidecadal Variability (AMV) over the last two millennia, and find several robust thermodynamic features associated with a positive Atlantic Multidecadal Oscillation (AMO) index that reveal a dynamically-consistent pattern of variability: the Atlantic and most continents warm; sea ice thins over the Arctic and retreats over the Greenland-Iceland-Norwegian Seas; and equatorial precipitation shifts northward. The latter is consistent with anomalous southward energy transport mediated by the atmosphere. Net downward shortwave radiation increases at both the top-of-atmosphere and surface, indicating a decrease in planetary albedo, likely due to a decrease in low clouds. Heat is absorbed by the climate system and the oceans warm. Wavelet analysis of the AMV time series shows a reddening of...

Weather and Forecasting, 2009

A specific event, called a low-visibility procedure (LVP), has been defined when visibility is un... more A specific event, called a low-visibility procedure (LVP), has been defined when visibility is under 600 m and/or the ceiling is under 60 m at Paris-Charles de Gaulle Airport, Paris, France, to ensure air traffic safety and to reduce the economic issues related to poor visibility conditions. The Local Ensemble Prediction System (LEPS) has been designed to estimate LVP likelihood in order to help forecasters in their tasks. This work evaluates the skill of LEPS for each type of LVP that takes place at the airport area during five winter seasons from 2002 to 2007. An event-based classification reveals that stratus base lowering, advection, and radiation fogs make up for 78% of the LVP cases that occurred near the airport during this period. This study also demonstrates that LEPS is skillful on these types of event for short-term forecasts. When the ensemble runs start with initialized LVP events, the prediction of advection fogs is as skillful as the prediction of radiation fog events...

Pure and Applied Geophysics, 2007

Journal of the Atmospheric Sciences, 2010

To gain insights into the poorly understood phenomenon of precipitation fog, this study assesses ... more To gain insights into the poorly understood phenomenon of precipitation fog, this study assesses the evaporation of freely falling drops departing from equilibrium as a possible contributing factor to fog formation in rainy conditions. The study is based on simulations performed with a microphysical column model describing the evolution of the temperature and mass of evaporating raindrops within a Lagrangian reference frame. Equilibrium defines a state where the latent heat loss of an evaporating drop is balanced by the sensible heat flux from the ambient air, hence defining a steady-state drop temperature. Model results show that the assumption of equilibrium leads to small but significant errors in calculated precipitation evaporation rates for drops falling in continuously varying ambient near-saturated or saturated conditions. Departure from equilibrium depends on the magnitude of the vertical gradients of the ambient temperature and moisture as well as the drop-size-dependent t...