Carla Cardinali

Characteristics of Occasional Poor Medium-Range Weather Forecasts for Europe

Medium-range weather prediction has become more skillful over recent decades, but forecast centers still suffer from occasional very poor forecasts, which are often referred to as “dropouts” or “busts.” This study focuses on European Centre for Medium-Range Weather Forecasts (ECMWF) day-6 forecasts for Europe. Although busts are defined by gross scores, bust composites reveal a coherent “Rex type” blocking situation, with a high over northern Europe and a low over the Mediterranean. Initial conditions for these busts also reveal a coherent flow, but this is located over North America and involves a trough over the Rockies, with high convective available potential energy (CAPE) to its east. This flow type occurs in spring and is often associated with a Rossby wave train that has crossed the Pacific. A composite on this initial flow type displays enhanced day-6 random forecast errors and some-what enhanced ensemble forecast spread, indicating reduced inherent predictability. Mesoscale convective systems, as...

LIDAR-MEASURED WIND PROFILES The Missing Link in the Global Observing System

The three-dimensional global wind field is the most important remaining measurement needed to accurately assess the dynamics of the atmosphere. Wind information in the tropics, high latitudes, and stratosphere is particularly deficient. Furthermore, only a small fraction of the atmosphere is sampled in terms of wind profiles. This limits our ability to optimally specify initial conditions for numerical weather prediction (NWP) models and our understanding of several key climate change issues. Because of its extensive wind measurement heritage (since 1968) and especially the rapid recent technology advances, Doppler lidar has reached a level of maturity required for a space-based mission. The European Space Agency (ESA)s Atmospheric Dynamics Mission Aeolus (ADM-Aeolus) Doppler wind lidar (DWL), now scheduled for launch in 2015, will be a major milestone. This paper reviews the expected impact of DWL measurements on NWP and climate research, measurement concepts, and the recent advances in technology that ...

Use and Impact of Automated Aircraft Data in a Global 4DVAR Data Assimilation System

Abstract The use of automated aircraft data [Aircraft Meteorological Data Relay (AMDAR) and Aircraft Communication Addressing and Reporting System (ACARS)] has recently been extended in ECMWFs operational 4DVAR data assimilation system. Herein, a modified data selection procedure is reported on that allows the use of more aircraft profiling data during the aircrafts ascending and descending phase, and more of the most frequent reports at cruise level. It is shown that the accuracy of analyzed jet streams is improved through these changes, as verified against independent (non–real time) aircraft data that had not been used in the experiments. The modifications are shown to have a clear positive impact on the short- and medium-range forecast performance. The revised aircraft usage was implemented operationally in January 2002. The impact in 4DVAR of profiles from American and European automated aircraft in ascending and descending phase has been tested in a data denial impact study, for January and July 2...

Impact of Targeted Winter Storm Reconnaissance Dropwindsonde Data on Midlatitude Numerical Weather Predictions

AbstractThe impact of assimilating data from the 2011 Winter Storm Reconnaissance (WSR) program on numerical weather forecasts was assessed. Parallel sets of analyses and deterministic 120-h numerical forecasts were generated using the ECMWF four-dimensional variational data assimilation (4D-Var) and Integrated Forecast System. One set of analyses was generated with all of the normally assimilated data plus WSR targeted dropwindsonde data, the other with only the normally assimilated data. Forecasts were then generated from the two analyses. The comparison covered the period from 10 January to 28 March 2011, during which 98 flights and 776 total dropwindsondes were deployed from four different air bases in the Pacific basin and the United States. The dropwindsondes were deployed in situations where guidance indicated the potential for high-impact weather and/or the potential for large subsequent forecast errors. Downstream target verification regions where the high-impact weather was expected were identif...

GNSS Radio Occultation Constellation Observing System Experiments

AbstractObserving system experiments within the operational ECMWF data assimilation framework have been performed for summer 2008 when the largest recorded number of Global Navigation Satellite System (GNSS) radio occultation observations from both operational and experimental satellites were available. Constellations with 0%, 5%, 33%, 67%, and 100% data volume were assimilated to quantify the sensitivity of analysis and forecast quality to radio occultation data volume. These observations mostly constrain upper-tropospheric and stratospheric temperatures and correct an apparent model bias that changes sign across the upper-troposphere–lower-stratosphere boundary. This correction effect does not saturate with increasing data volume, even if more data are assimilated than available in today’s analyses. Another important function of radio occultation data, namely, the anchoring of variational radiance bias corrections, is demonstrated in this study. This effect also does not saturate with increasing data vo...

The Concordiasi Field Experiment over Antarctica: First results from innovative atmospheric measurements

Florence Rabier , Steve Cohn , Philippe Cocquerez , Albert Hertzog, Linnea Avallone, Terry Deshler, Jennifer Haase , Terry Hock, Alexis Doerenbecher , Junhong Wang , Vincent Guidard, Jean-Noël Thépaut , Rolf Langland, Andrew Tangborn , Gianpaolo Balsamo , Eric Brun, David Parsons , Jérôme Bordereau , Carla Cardinali , François Danis , Jean-Pierre Escarnot , Nadia Fourrié, Ron Gelaro, Christophe Genthon , Kayo Ide, Lars Kalnajs, Charlie Martin, LouisFrançois Meunier , Jean-Marc Nicot , Tuuli Perttula, Nicholas Potts , Patrick Ragazzo , David Richardson, Sergio Sosa-Sesma , André Vargas 3

Jet Stream Analysis and Forecast Errors Using GADS Aircraft Observations in the DAO, ECMWF, and NCEP Models

Abstract Peak analyzed jet stream wind speeds are compared with independent aircraft observations over Canada and the continental United States. The results permit a study of the accuracy of analyzed jet streak strength for the data-sparse 85% of the earths surface versus the data-dense 15%. The observations come from the Global Aircraft Data Set (GADS) experiment, which since 1996 has collected flight data recorder information from every flight of 56 British Airways 747-400 aircraft. The study is timely because automated aircraft observations are reaching their near-asymptotic limits (there are not many uncovered commercial aircraft routes left), and we are about to enter a new, third-generation, satellite-sounding-instrument era. Future reanalyses will mix time periods from both eras. This study gives an estimate of the analysis accuracy of data assimilation using second-generation satellite systems. The results show that major current generation assimilation models have peak wind speed errors of −5% t...

A Global Ocean Observing System for Measuring Sea Level Atmospheric Pressure: Effects and Impacts on Numerical Weather Prediction

AbstractSince 1994 the U.S. Global Drifter Program (GDP) and its international partners cooperating within the Data Buoy Cooperation Panel (DBCP) of the World Meteorological Organization (WMO) and the United Nations Education, Scientific and Cultural Organization (UNESCO) have been deploying drifters equipped with barometers primarily in the extratropical regions of the world’s oceans in support of operational weather forecasting. To date, the impact of the drifter data isolated from other sources has never been studied. This essay quantifies and discusses the effect and the impact of in situ sea level atmospheric pressure (SLP) data from the global drifter array on numerical weather prediction using observing system experiments and forecast sensitivity observation impact studies. The in situ drifter SLP observations are extremely valuable for anchoring the global surface pressure field and significantly contributing to accurate marine weather forecasts, especially in regions where no other in situ observ...

On the Impact of the Diabatic Component in the Forecast Sensitivity Observation Impact Diagnostics

Over the years, a comprehensive set of the linearized physical parametrization schemes has been developed at ECMWF . These linearized schemes, operationally used in data assimilation, parametrize both the dry physical processes (vertical diffusion, gravity wave drag , shortwave and longwave radiation) and the moist processes (convection, large-scale condensation and clouds) consistently with the physical parametrization of the nonlinear model (though some simplifications are applied). In this work, the representation of the moist physical processes in the adjoint assimilation model is compared with the representation of humidity in the energy norm used to compute the forecast sensitivity to observations in the short-range forecasts. Forecast Sensitivity Observation Impact using the adjoint model with only dry processes (dry adjoint) but moist energy norm in the sensitivity gradient calculation is examined in contrast with the observation impact obtained when moist processes (moist adjoint ) and dry energy norm are used. The performed study indicates that the use of the humidity term in the norm produces unrealistic humidity and temperature sensitivity gradients, which largely affect the observation forecast impact results.

Data denial experiments for extratropical transition

ABSTRACT Data denial experiments using the European Centre for Medium-Range Weather Forecasts (ECMWF) model are designed to investigate the value of targeted observations for historical extratropical transition (ET) cases over the Atlantic. The impact of removing data from specified locations linked to the ET development is therefore examined. It is shown that the impact of denying data in the near tropical cyclone (TC) environment is, on average, as important as denying data in mid-latitude sensitive regions determined using extratropical singular vectors (SV). The impact of data denial over TC regions propagates downstream from the Atlantic towards Europe, with a maximum degradation at day 4. This degradation is mainly attributed to the data denial at the TC stage, i.e. before ET is completed. When data are denied on mid-latitude sensitive regions, the largest degradation is found around day 2 and also after the day 4 forecast. In general, the loss of information content is larger when data are denied in mid-latitude sensitive areas because these identify dynamically active regions. In both denial experiments, aircraft and satellite radiance data are the most influential observations. For the selected case of Hurricane Irene, the largest degradations are found for forecasts initialised while Irene reached its peak intensity. If observations are denied in the near storm environment, the TC mostly disappears from the analysis and the subsequent forecast. This allows the impact of Irene on the formation of the downstream cut-off low to be investigated.