Chapter 3 3D variational assimilation (with the first-guess at appropriate time) Chapter 4 Background term Chapter 5 Observation operators and observation cost function (J o) Chapter 6 Background, analysis and forecast errors Chapter 7 Gravity-wave control Chapter 8 Diagnostics Chapter 9 Observation processing Chapter 10 Observation screening Chapter 11 Land-surface analysis Chapter 12 Analysis...

This paper proposes the hypothesis that the low-frequency variability of the North Atlantic Oscillation (NAO) arises as a result of variations in the occurrence of upper-level Rossby wave–breaking events over the North Atlantic. These events lead to synoptic situations similar to midlatitude blocking that are referred to as high-latitude blocking episodes. A positive NAO is envisaged as being a...

The responsible mechanism for the formation of the enhanced-V infrared cloud-top feature observed above tropopause-penetrating thunderstorms is not well understood. A new method for the combination of volumetric radar reflectivity from individual radars into three-dimensional composites with high vertical resolution (1 km) is introduced and used to test various formation mechanisms proposed in ...

This paper reports preliminary results for a Limited area model Ensemble Prediction System (LEPS), based on RAMS (Regional Atmospheric Modelling System), for eight case studies of moderate-intense precipitation over Calabria, the southernmost tip of the Italian peninsula. LEPS aims to transfer the benefits of a probabilistic forecast from global to regional scales in countries where local orogr...

7 In recent years, the global positioning system (GPS) has been exploited via radio occultation techniques to obtain proÿles of refractivity, temperature, pressure and water vapor in the neutral atmosphere and electron density in the ionosphere. The 9 GPS=MET experiment, which placed a GPS receiver in a low-Earth orbit, provided a wealth of data which was used to test this concept and the accur...

In order to validate wind vectors derived from the NASA scatterometer (NSCAT), statistical distributions of wind speeds and directions retrieved by the NSCAT-2 geophysical model function have been investigated by comparison with wind data retrieved by the other model functions such as SASS-2 and NSCAT-1 and those derived from the wind analyses of the European Centre for Medium Range Weather For...

The intensive observing period number 2a (IOP2a) of the Mesoscale Alpine Programme (MAP Bougeault et al., 2001) took place on 17 September 1999 over the Lago Maggiore Area in northern Italy. Between 12 UTC and 00 UTC a convective line developed over the first slopes of the Lago Maggiore mountains and propagated south-eastwards. During the early night, the system intensified and produced 70 mm o...

[1] In this study, the midlatitude cloud fields produced by a climate (GISS) and a weather (ECMWF) model are evaluated against satellite observations. Monthly ensembles of model cloud property distributions for the four seasons are compared with similar ensembles from satellite retrievals. The weather model is run in both forecast and ‘‘climate’’ mode in order to evaluate the importance of the ...

Available rawinsonde, automatic weather station (AWS), ship, and synthesized long-term observations are used to evaluate the Antarctic numerical analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF) and the U.S. National Centers for Environmental Prediction (NCEP) from 1985 to 1994. Twice-daily variations in the ECMWF surface pressure analyses compare closely with AWS units...