Search results for "wave"
showing 10 items of 6009 documents
Potential Vorticity Dynamics of Forecast Errors: A Quantitative Case Study
2018
Abstract Synoptic-scale error growth near the tropopause is investigated from a process-based perspective. Following previous work, a potential vorticity (PV) error tendency equation is derived and partitioned into individual contributions to yield insight into the processes governing error growth near the tropopause. Importantly, we focus here on the further amplification of preexisting errors and not on the origin of errors. The individual contributions to error growth are quantified in a case study of a 6-day forecast. In this case, localized mesoscale error maxima have formed by forecast day 2. These maxima organize into a wavelike pattern and reach the Rossby wave scale around forecast…
Current and emerging developments in subseasonal to decadal prediction
2020
Weather and climate variations on subseasonal to decadal time scales can have enormous social, economic, and environmental impacts, making skillful predictions on these time scales a valuable tool for decision-makers. As such, there is a growing interest in the scientific, operational, and applications communities in developing forecasts to improve our foreknowledge of extreme events. On subseasonal to seasonal (S2S) time scales, these include high-impact meteorological events such as tropical cyclones, extratropical storms, floods, droughts, and heat and cold waves. On seasonal to decadal (S2D) time scales, while the focus broadly remains similar (e.g., on precipitation, surface and upper-…
Foam effect on the sea surface emissivity in the 8–14μm region
2007
[1] The effect of foam on the sea surface emission has been studied in the microwave region, but its effect on thermal infrared emissivity and temperature has not been sufficiently analyzed in the literature. This paper presents thermal infrared measurements of foam-covered seawaters carried out under controlled conditions using a multichannel radiometer working in the 8–14 μm region. The experimental data show a negligible foam effect at low observation angles but a significant increase of emissivity with foam at angles above 45°. Differences between foam and foam-free emissivities are about +0.04 for observation angles of 65°, depending slightly on the radiometric spectral band. The effec…
Northward bursts of the West African monsoon leading to rainfall over the Hoggar Massif, Algeria
2009
The Hoggar Massif is a comparatively populated region in the Sahara, where water supply is a critical problem due to the lack of nearby sources and unaffordable water pumping. In the present paper, we analyse the influence of the West African monsoon (WAM) on precipitation over the Hoggar during summer. We investigate (1) two rainfall events during 23-27 July 2006, accounting for almost half of the precipitation of this year, and (2) the representativity of this period with regard to ERA-40 ECMWF re-analyses (1979 to 2001). By the end of July 2006, two consecutive northward bursts of the WAM flow reached the Hoggar and caused an increase in low-level humidity. In the afternoon of these days…
The Extratropical Transition of Tropical Cyclones. Part II: Interaction with the Midlatitude Flow, Downstream Impacts, and Implications for Predictab…
2019
Abstract The extratropical transition (ET) of tropical cyclones often has an important impact on the nature and predictability of the midlatitude flow. This review synthesizes the current understanding of the dynamical and physical processes that govern this impact and highlights the relationship of downstream development during ET to high-impact weather, with a focus on downstream regions. It updates a previous review from 2003 and identifies new and emerging challenges and future research needs. First, the mechanisms through which the transitioning cyclone impacts the midlatitude flow in its immediate vicinity are discussed. This “direct impact” manifests in the formation of a jet streak …
Enhanced Tropospheric Wave Forcing of Two Anticyclones in the Prephase of the January 2009 Major Stratospheric Sudden Warming Event
2017
Monthly Weather Review, 145 (5)
Saharan dust absorption and refractive index from aircraft-based observations during SAMUM 2006
2009
During the Saharan Mineral Dust Experiment (SAMUM) conducted in summer 2006 in southeast Morocco, the complex refractive index of desert dust was determined from airborne measurements of particle size distributions and aerosol absorption coefficients at three different wavelengths in the blue (467 nm), green (530 nm) and red (660 nm) spectral regions. The vertical structure of the dust layers was analysed by an airborne high spectral resolution lidar (HSRL). The origin of the investigated dust layers was estimated from trajectory analyses, combined with Meteosat 2nd Generation (MSG) scenes and wind field data analyses. The real part n of the dust refractive index was found almost constant w…
A Precise Photometric Ratio via Laser Excitation of the Sodium Layer II: Two-photon Excitation Using Lasers Detuned from 589.16 nm and 819.71 nm Reso…
2020
This article is the second in a pair of articles on the topic of the generation of a two-color artificial star (which we term a "laser photometric ratio star," or LPRS) of de-excitation light from neutral sodium atoms in the mesosphere, for use in precision telescopic measurements in astronomy and atmospheric physics, and more specifically for the calibration of measurements of dark energy using type Ia supernovae. The two techniques respectively described in both this and the previous article would each generate an LPRS with a precisely 1:1 ratio of yellow (589/590 nm) photons to near-infrared (819/820 nm) photons produced in the mesosphere. Both techniques would provide novel mechanisms f…
Variability of the African convection centre as viewed by outgoing longwave radiation records and relationships with sea-surface temperature patterns
1995
International audience; The main African convection centre (ACC) is delimited by the 5"-square areas with outgoing longwave radiation less than 235 W m-' in the domain 17.5°N-17.5"S and 18"W-46"E. Four parameters (latitude and longitude of the centre of gravity, mean intensity, and extension) were analysed during the period June 1974 to December 1991. The relationships between the variability of the ACC and the main sea-surface temperature (SST) patterns were then studied. Correlation and composite analyses demonstrate that the first principal component of SST, representing mainly the variability of the eastern and the central tropical Pacific, is associated strongly with the extension and …
Analysis of broadband surface BRDFs derived from TOA SW CERES measurements for surfaces classified by the IGBP land cover
2012
Most studies on the reflectance properties of the Earth's surface are addressed estimating the bidirectional reflectance distribution function (BRDF) of high spatial resolution and high spectral resolution satellite measurements. This article assesses the development of broadband (BB) BRDFs from radiances corresponding to large footprints classified according to the International Geosphere-Biosphere Programme (IGBP) land-cover classification. Top-of-atmosphere (TOA) shortwave (SW) CERES (Clouds and the Earth's Radiant Energy System) measurements are employed to invert the bidirectional reflectance factor (BRF) Rahman–Pinty–Verstraete (RPV) model for regions identified with the same IGBP typ…