Exploiting existing ground-based remote sensing networks to improve high-resolution weather forecasts

A new generation of high-resolution (1 km) forecast models promises to revolutionize the prediction of hazardous weather such as windstorms, flash floods, and poor air quality. To realize this promise, a dense observing network, focusing on the lower few kilometers of the atmosphere, is required to verify these new forecast models with the ultimate goal of assimilating the data. At present there are insufficient systematic observations of the vertical profiles of water vapor, temperature, wind, and aerosols; a major constraint is the absence of funding to install new networks. A recent research program financed by the European Union, tasked with addressing this lack of observations, demonstrated that the assimilation of observations from an existing wind profiler network reduces forecast errors, provided that the individual instruments are strategically located and properly maintained. Additionally, it identified three further existing European networks of instruments that are currently underexploited, but with minimal expense they could deliver quality-controlled data to national weather services in near–real time, so the data could be assimilated into forecast models. Specifically, 1) several hundred automatic lidars and ceilometers can provide backscatter profiles associated with aerosol and cloud properties and structures with 30-m vertical resolution every minute; 2) more than 20 Doppler lidars, a fairly new technology, can measure vertical and horizontal winds in the lower atmosphere with a vertical resolution of 30 m every 5 min; and 3) about 30 microwave profilers can estimate profiles of temperature and humidity in the lower few kilometers every 10 min. Examples of potential benefits from these instruments are presented

The convective storm initiation project

Copyright @ 2007 AMSThe Convective Storm Initiation Project (CSIP) is an international project to understand precisely where, when, and how convective clouds form and develop into showers in the mainly maritime environment of southern England. A major aim of CSIP is to compare the results of the very high resolution Met Office weather forecasting model with detailed observations of the early stages of convective clouds and to use the newly gained understanding to improve the predictions of the model. A large array of ground-based instruments plus two instrumented aircraft, from the U.K. National Centre for Atmospheric Science (NCAS) and the German Institute for Meteorology and Climate Research (IMK), Karlsruhe, were deployed in southern England, over an area centered on the meteorological radars at Chilbolton, during the summers of 2004 and 2005. In addition to a variety of ground-based remote-sensing instruments, numerous rawin-sondes were released at one- to two-hourly intervals from six closely spaced sites. The Met Office weather radar network and Meteosat satellite imagery were used to provide context for the observations made by the instruments deployed during CSIP. This article presents an overview of the CSIP field campaign and examples from CSIP of the types of convective initiation phenomena that are typical in the United Kingdom. It shows the way in which certain kinds of observational data are able to reveal these phenomena and gives an explanation of how the analyses of data from the field campaign will be used in the development of an improved very high resolution NWP model for operational use.This work is funded by the National Environment Research Council following an initial award from the HEFCE Joint Infrastructure Fund

ADAPTIVE OPTICS WITH SEGMENTED MIRROR OR DEFORMABLE MIRROR

Deux types de miroirs adaptatifs sont étudiés : un miroir segmenté avec 19 moteurs (COAT 19) et un miroir continûment déformable à 7 moteurs. Chaque miroir du COAT 19 est mû par un actuateur piezo-électrique qui assure à la fois les fonctions de correction et de modulation dans la bande 12-24 kHz. L'analyse de la surface d'onde optique est faite grâce à la détection des signaux de modulation dans la lumière rétrodiffusée par la cible. On en déduit les ordres de correction des perturbations dues à l'atmosphère, au laser et aux miroirs... Dans le cas du miroir déformable, les fonctions de correction et de modulation sont assurées par des miroirs séparés. Ces miroirs comportent un système de refroidissement pour pouvoir être utilisés avec des lasers de haute énergie.Two kinds of adaptive optics (COAT) are presented : one with segmented mirrors (COAT = 19) with 19 mirrors and actuators and the other with a continuously deformable mirror and 7 actuators. Each mirror of COAT 19 is moved by a piezoelectric actuator performing correction and modulation (dithering in the 12-24 kHz band). Detection of signal modulations in the light backscattered from the target gives means to lock the system and then to correct disturbing effects due to atmosphere, laser, mirrors… In the second kind of COAT (deformable mirror), the works of correction and modulation (dithering) are performed by two separate mirrors. They both are cooled to support high-energy laser beam