World Meteorological Organization

The World Meteorological Organization (WMO) is a specialized agency of the United Nations responsible for promoting international cooperation on atmospheric science, climatology, hydrology and geophysics. The WMO originated from the International Meteorological Organization, a nongovernmental organization founded in 1873 as a forum for exchanging weather data and research. Proposals to reform the status and structure of the IMO culminated in the World Meteorological Convention of 1947, which formally established the World Meteorological Organization. The Convention entered into force on 23 March 1950, and the following year the WMO began operations as an intergovernmental organization within the UN system. The WMO is made up of 193 countries and territories, and facilitates the "free and unrestricted" exchange of data, information, and research between the respective meteorological and hydrological institutions of its members. It also collaborates with nongovernmental partners and

Considering snow depositions and transport mechanisms in meteorological analysis of predicting snow loads on buildings

Michael Lehning, Borui Zhang, Qingwen Zhang

The meteorological conditions determine snow evolutions on and around buildings. Those climatic impacts have been independently considered in the current design codes of buildings, namely the wind pressure and the snow load. But snow load estimates are only based on precipitation assessments without considering the joint effect of wind and snow precipitation which lead to wind dominated deposition and snow transport. Thus, the statisticsbased data provided by those building codes seem practically inadequate or at least incomplete. Using the data provided by upper-air and ground meteorological stations in northern China, including snowfall, wind velocity, and temperature, as indicators, we propose a series of statistical relationships covering aspects of snow precipitation and snow drifting. For those meteorological indicators that can affect building snow evolutions, more detailed analyses on their spatial and temporal changes have been achieved. The regionalization of snow precipitation features in northern China has also been proposed based on the clustering analysis on meteorological joint effects. The result shows that the snowfall in most northern regions of China is generally not heavy and in the form of a uniform deposition. The wind dominated depositions around buildings are more likely to appear in the regions around the Bohai Sea.

ELSEVIER2022

Automated Raman Lidar for Day and Night Operational Observation of Tropospheric Water Vapor for Meteorological Applications

Todor Dinoev

Water vapor is a fundamental constituent of the atmosphere and is the most abundant green house gas thus having an important influence on climate. It is as well a key prognostic variable for numerical weather prediction models (NWP). Currently, the vertical profiles of tropospheric water vapor are provided by twice a day radiosondes. The routine observations have rather low temporal resolution that is insufficient to resolve fast-running meteorological phenomena. The aim of the thesis work was to design and build a Raman lidar instrument capable of continuous vertical profiling of tropospheric water vapor field with high temporal and vertical resolution. The provided observations will improve the database available for direct meteorological applications and could increase the accuracy of numerical weather prediction. RALMO – RAman Lidar for Meteorological Observations is developed as fully automated, eye-safe instrument for operational use by the Swiss meteorological service – MeteoSwiss. The lidar is able to provide vertical profiles of water vapor mixing ratio with time resolution from 5 to 30 min and vertical resolution from 15 m in boundary layer and 75 – 500 m in free troposphere. The daytime vertical operational range of the lidar extends from about 50 m to mid-troposphere and the detection limit is 0.5 g/kg. In night-time conditions the vertical operational range extends up to the tropopause with 0.01 g/kg detection limit. To allow daytime operation with extended vertical range and required detection limit the lidar is designed with narrow field-of-view receiver, narrow band detection, and it uses high pulse power laser with wavelength in the UV but out of solar blind region. The lidar transmitter uses flash-lamps pumped frequency tripled Nd: YAG laser generating 8 ns pulses with 0.3 J energy and 355 nm wavelength. To reduce the beam irradiance, required for eye-safe operation, and to reduce the divergence required for narrow field of view receiver, the laser beam is expanded by 15x refractive type expander. The backscattered laser light is collected by four 30 cm in diameter telescopes with focal length of 1 m. For better long term alignment stability the telescopes are tightly arranged around the beam expander in compact assembly. The field-of-view of the telescopes is reduced to 0.2 mrad to decrease the collected sky-scattered sunlight thus allowing daytime measurements up to mid troposphere. Fibers transmit the light collected by the telescopes to the lidar polychromator. Fiber coupling was preferred against free space connection because it separates the units mechanically and increases the overall lidar stability. In addition the fibers perform aperture scrambling which prevents range dependence of the receiver parameters. An additional "near range" fiber is installed in one of the telescopes to enhance the near range signal and to allow daytime measurements starting from approximately 50 m above the lidar. A high throughput diffraction grating polychromator is designed for narrow band isolation of water vapor, nitrogen, and oxygen Q branches of ro-vibrational Raman spectra. Water vapor mixing ratio is derived from the ratio of water vapor to nitrogen Raman signals and the oxygen signal is used to correct for aerosol differential extinction at water and nitrogen wavelengths. The water vapor detection channel passband is 0.3 nm. The narrow band detection increases the lidar sensitivity and operational range in daytime conditions. For maximum throughput of the polychromator, the exit and entrance slits are matched and the polychromator entrance accepts the divergent beam from the fibers without losses. Photomultipliers at the exit of the polychromator detect the Raman lidar signals, which are then acquired by transient recorders (Licel). The signals are simultaneously recorded in analog and photon-counting modes. The analog signals are used in daytime conditions with sky background signal that saturates completely the photon counter, whereas in night-time conditions, photon counting signals are used. Two computers provide for the automated operation of the lidar instrument. The first one controls all lidar units relevant to the lidar operation, including the laser and the data acquisition. For this purpose, Lidar Automat software has been developed under LabView and requires only activation by an operator. Automated data treatment software, developed under Matlab, is run on the second lidar computer. It reads the initial lidar data, treats them, and stores the final result in files ready for upload to the meteorological service. The files contain vertical profiles of water vapor mixing ratio and relative error. The lidar was completed in July 2007 and installed at the aerological station of MeteoSwiss in Payerne. Since October 2007 the lidar has been in experimental operation and the software for automated data treatment was completed. Since September 2008 the instrument has been fully operational, providing continuous vertical water vapor mixing ratio profiles uploaded to MeteoSwiss every 30 min. Regular comparisons with Vaisala RS-92 and Snow White® radiosondes were performed during the experimental lidar operation at Payerne. Long-term stability study of the calibration coefficient was performed as well.

EPFL2009

Experimental History and the History of Experience: Reconstructing the Scientific Expeditions of the 1770s to Mont Buet

Jérôme Baudry

On September 20, 1770, the brothers Jean-André and Guillaume-Antoine Deluc, two scientists from Geneva, finally reached the summit of Mont Buet (3096m) after two unsuccessful attempts. From this vantage point overlooking the Alps and Mont Blanc, they performed several physics experiments and accumulated meteorological, geological, and ethnographic observations. The picturesque account of their ascent sparked further vocations: in the 1770s, the Genevans Marc-Théodore Bourrit, Horace-Bénédict de Saussure and Marc-Auguste Pictet also traveled to Mont Buet to replicate the Deluc's experiments and to make their own observations. These expeditions contributed to transform the mountain into a “laboratory of nature,” in Saussure’s own words. In September 2020, August 2021 and September 2022, two hundred and fifty years after the first ascent, a group of historians of science followed several paths to the summit of Mont Buet to reconstruct the historical expeditions of the Genevan scientists. They took with them two replicas of the barometer designed by Jean-André Deluc, they replicated the experiments of the 1770s and they documented their ascent with the help of a photographer, a draughtswoman, and a sound artist. In this talk, I will discuss the implications, the outcomes and the limits of this experience of historical reconstruction, focusing on three initial proposals of the project: 1) reconstructing scientific activity in the field, rather than in the controlled context of the laboratory; 2) capturing the mountain as a lived milieu rather than as a geographical location; 3) integrating historical research and scientific mediation by producing a contemporary archive that dialogues with the historical actors’ inscriptions (texts, engravings, drawings, and paintings).

2022

Automated Raman Lidar for Day and Night Operational Observation of Tropospheric Water Vapor for Meteorological Applications

Todor Dinoev

EPFL2009