Land surface spinup for episodic modeling Angevine, W. M; Bazile, E; Legain, D ...
Atmospheric chemistry and physics,
08/2014, Letnik:
14, Številka:
15
Journal Article, Publication
Recenzirano
Odprti dostop
Soil moisture strongly controls the surface fluxes in mesoscale numerical models, and thereby influences the boundary layer structure. Proper initialization of soil moisture is therefore critical for ...faithful simulations. In many applications, such as air quality or process studies, the model is run for short, discrete periods (a day to a month). This paper describes one method for soil initialization in these cases – self-spinup. In self-spinup, the model is initialized with a coarse-resolution operational model or reanalysis output, and run for a month, cycling its own soil variables. This allows the soil variables to develop appropriate spatial variability, and may improve the actual values. The month (or other period) can be run more than once if needed. The case shown is for the Boundary Layer Late Afternoon and Sunset Turbulence experiment, conducted in France in 2011. Self-spinup adds spatial variability, which improves the representation of soil moisture patterns around the experiment location, which is quite near the Pyrenees Mountains. The self-spinup also corrects a wet bias in the large-scale analysis. The overall result is a much-improved simulation of boundary layer structure, evaluated by comparison with soundings from the field site. Self-spinup is not recommended as a substitute for multi-year spinup with an offline land data assimilation system in circumstances where the data sets required for such spinup are available at the required resolution. Self-spinup may fail if the modeled precipitation is poorly simulated. It is an expedient for cases when resources are not available to allow a better method to be used.
The EUREQUA project raises the issue of the definition and evaluation of the environmental quality of neighbourhoods. The approach consists of integrating and cross-referencing observable data ...characterising the physical environment and people’s perception of their quality of life. The study area is a neighbourhood in Toulouse (France) with high social and typo-morphological diversity, subject to noise and air pollution nuisances. Three 3-day field campaigns were organised in January, April, and June 2014. Instrumented and commented walks took place three times per day. For each one, measurements of physical environmental parameters and surveys were performed simultaneously at six locations in the neighbourhood. The study focuses on microclimate and thermal comfort issues. It aims to compare in situ meteorological data of air temperature, humidity, wind speed, and mean radiant temperature, with quantitative results rating human perception of heat, humidity, wind, and thermal comfort. The variability in perception and measurements is mainly driven by seasonal effects, especially for heat and humidity, and, to a lesser extent, for wind. Wind perception and measurement also vary spatially, thus highlighting site effects. Linear models indicate a positive link between heat perception and mean radiant temperature, as well as between wind perception and mean and standard deviation of wind speed (with a higher sensitivity of people to wind under winter climate conditions). Finally, it is found that perception of thermal comfort is only slightly linked to the different microclimate dimensions, and is rather driven by other appreciation factors and emotional criteria related to the general environmental quality of the study area.
Air–sea exchanges play an important role during intense weather events over the Mediterranean Sea, especially in supplying heat and moisture for heavy precipitation events, which often affect the ...area. Observations collected during the first Hydrological cycle in the Mediterranean Experiment (HyMeX) Special Observation Period (SOP1) over the Western Mediterranean area in autumn 2012 provide an unprecedented dataset for assessing the capabilities of numerical weather prediction systems to represent the air–sea interface and marine boundary layer during the heavy precipitation season. A HyMeX‐dedicated version of Application de la Recherche à l'Opérationnel à Méso‐Échelle, in French (AROME) covering the whole western Mediterranean basin, named AROME–WMED, was evaluated through comparisons against moored buoys, drifting buoys and ship measurements deployed during the HyMeX campaign. A general, good agreement is found for near‐surface meteorological parameters, whereas significant discrepancies are observed during strong air–sea exchange periods. The two main reasons are that (1) sea‐surface temperature (SST) is kept constant during the model runs and (2) sensible heat flux is overestimated in strong wind regimes by the AROME turbulent flux parametrization.
Air–sea exchanges during SOP1 were characterized thanks to AROME–WMED short‐range (1–24 h) forecasts. This shows some areas of strong air–sea fluxes in the Gulf of Lion and the Balearic, Ligurian and Tyrrhenian Seas. The Gulf of Lion is the area showing the highest variability of air–sea fluxes, due to dominant strong regional winds (Mistral/Tramontane). Whereas some heavy precipitation events occur without significant air–sea fluxes, all strong air–sea exchange events include, or occur only 1 or 2 days before, heavy precipitation events. A detailed analysis of an Intense Observation Period (IOP) dedicated to a heavy precipitation event (IOP13, from 12–15 October) illustrates how both dynamic (wind) and thermodynamic (temperature and humidity gradient effect) contributions influence air–sea flux evolution.
The Development of Methodologies for Water Vapour Measurement (DEMEVAP) project aims at assessing and improving humidity sounding techniques and establishing a reference system based on the ...combination of Raman lidars, ground-based sensors and GPS. Such a system may be used for climate monitoring, radiosonde bias detection and correction, satellite measurement calibration/validation, and mm-level geodetic positioning with Global Navigation Satellite Systems. A field experiment was conducted in September-October 2011 at Observatoire de Haute-Provence (OHP). Two Raman lidars (IGN mobile lidar and OHP NDACC lidar), a stellar spectrometer (SOPHIE), a differential absorption spectrometer (SAOZ), a sun photometer (AERONET), 5 GPS receivers and 4 types of radiosondes (Vaisala RS92, MODEM M2K2-DC and M10, and Meteolabor Snow White) participated in the campaign. A total of 26 balloons with multiple radiosondes were flown during 16 clear nights. This paper presents preliminary findings from the analysis of all these data sets. Several classical Raman lidar calibration methods are evaluated which use either Vaisala RS92 measurements, point capacitive humidity measurements, or GPS integrated water vapour (IWV) measurements. A novel method proposed by Bosser et al. (2010) is also tested. It consists in calibrating the lidar measurements during the GPS data processing. The methods achieve a repeatability of 4-5%. Changes in the calibration factor of IGN Raman lidar are evidenced which are attributed to frequent optical re-alignments. When modelling and correcting the changes as a linear function of time, the precision of the calibration factors improves to 2-3%. However, the variations in the calibration factor, and hence the absolute accuracy, between methods and types of reference data remain at the level of 7%. The intercomparison of radiosonde measurements shows good agreement between RS92 and Snow White measurements up to 12 km. An overall dry bias is found in the measurements from both MODEM radiosondes. Investigation of situations with low RH values (< 10%RH) in the lower and middle troposphere reveals, on occasion, a lower RH detection limit in the Snow White measurements compared to RS92 due to a saturation of the Peltier device. However, on other occasions, a dry bias is found in RS92, instead. On average, both RS92 and Snow White measurements show a slight moist bias at night-time compared to GPS IWV, while the MODEM measurements show a large dry bias. The IWV measurements from SOPHIE (night-time) and SAOZ (daytime) spectrometers, AERONET photometer (daytime) and calibrated Raman lidar (night-time) showed excellent agreement with the GPS IWV measurements.
11 ultra‐high‐frequency (UHF) and very‐high‐frequency (VHF) wind‐profiler radars were in operation for 13–18 months during the international Hydrological Cycle in Mediterranean Experiment (HyMeX) ...field campaign, devoted to the study of the atmospheric and marine water cycle in the western Mediterranean basin. These profilers provided vertical profiles of wind vector, turbulence, precipitation and the height of the atmospheric boundary layer and tropopause. The inland three VHF profilers aimed to document the upstream or downstream synoptic flow conditions. Five UHF profilers for lower atmosphere description were deployed along the French Mediterranean coast and Corsica Island. They were used to retrieve the 3D atmospheric wind fields over the basin, by assuming linearity of the fields inside a limited spatial and temporal domain. The objective of this article is to establish to what extent the 3D wind fields derived from the coastline profiler network are representative of the offshore kinematics. This assessment is performed by comparing more than one year of continuous profiler observations during different weather conditions with balloon radiosoundings and in situ aircraft or boundary‐layer pressurized balloon measurements.
A new system for high-frequency boundary layer profiling based upon radiosondes and free balloons was tested during the field phases of the Boundary Layer Late Afternoon and Sunset Turbulence ...experiment (BLLAST 2011, Lannemezan, France) and of the Hydrological cycle in the Mediterranean Experiment (HyMeX, 2012). The system consists of a conventional Vaisala receiver and a GPS radiosonde (pressure, wind, humidity and temperature), that is tied to a couple of inflated balloons. The principle of the sounding system is to permit the first balloon to detach from the rawinsonde at a predetermined altitude, allowing for the rawinsonde to slowly descend with the second balloon to perform a second, new sounding. The instrumentation is then eventually recovered. The expecting landing area is anticipated before the flight by estimating the trajectory of the probe from a forecasted wind profile and by specifying both the balloon release altitude and the mean ascent and descent rates of the system. The real landing point is determined by the last transmission of the radiosonde GPS and the visual landmark provided by the second balloon. Seventy-two soundings were performed during BLLAST (62) and HyMeX (10), with a recovery rate of more than 80% during the BLLAST field campaign. Recovered radiosondes were generally reused several times, often immediately after recovery, which definitely demonstrates the high potential of this system.
The CAPITOUL experiment is a joint experimental effort in urban climate, including the energetic exchanges between the surface and the atmosphere, the dynamics of the boundary layer over the city and ...its interactions with aerosol chemistry. The campaign took place in the city of Toulouse in southwest France, for one year, from February 2004 to February 2005. This allowed the study of both the day-to-day and seasonal variability of urban climate processes. The observational network included surface stations (meteorology, energy balance, chemistry), profilers and, during intensive observing periods, aircraft and balloons. The urban Surface Energy Balance differs between summer and winter: in summer, the solar heat stored during the previous daytime period is enough to maintain the heat release at night, but in winter, almost all the energy comes from the anthropogenic heat released by space heating. Both processes produce the well known Urban Heat Island (UHI). The city is shown to impact the entire boundary layer on specific days, when an urban breeze is observed. In wintertime, fog is found to be modified due to the vertical structure of the nocturnal boundary layer above the city (which is slightly unstable and not stable). The measurements of aerosol properties in and downwind the city permitted documentation of the urban aerosol as well as the chemical transformation of these aerosols, in particular the ageing of carbonaceous aerosols during transport. The Toulouse aerosol is mainly composed of carbonaceous particles. There is important seasonal variation in the ratio of black carbon to organic carbon, in the concentration of sulfates and nitrates and in the related radiative aerosol impacts. SF₆ was released as a tracer in a suburban area of Toulouse during anticyclonic conditions with weak winds. The tracer measurements show dispersion was mainly driven by the surface sensible heat flux, and was highly sensitive to the urban heat island and also to the transport of boundary layer clouds. Modeling was fully integrated into the campaign. Surface energy balance and urban boundary layer processes have already been used to complement the analyses of the physical processes observed during the campaign. Companion papers detail most of these observation or modeling studies.
This paper demonstrates that atmospheric inversions of CO2 are a reliable tool for estimating regional fluxes. We compare results of an inversion over 18 days and a 300 × 300 km2 domain in southwest ...France against independent measurements of fluxes from aircraft and towers. The inversion used concentration measurements from 2 towers while the independent data included 27 aircraft transects and 5 flux towers. The inversion reduces the mismatch between prior and independent fluxes, improving both spatial and temporal structures. The present mesoscale atmospheric inversion improves by 30% the CO2 fluxes over distances of few hundreds of km around the atmospheric measurement locations.
Concentrations and turbulent fluxes of accumulation mode particles were measured during the 2004–2005 ‘Canopy and Aerosol Particle Interaction in Toulouse Urban Layer’ project (CAPITOUL) at the top ...of two intersecting street canyons and in the urban boundary layer (UBL) in Toulouse, France. Particle numbers were strongly affected by boundary layer depth and showed limited sensitivity to local emissions. Differences in the diurnal patterns of particle numbers were observed between the finer fraction (0.3–0.4 μm) and coarser fraction (1.6–2.0 μm) of accumulation mode particles, indicating different processes of formation, evolution and transportation may be dominant. Highest particle numbers were observed in the narrow street canyon which had more limited local emissions and comparatively small particle fluxes. However, the improved ventilation rate in the wider canyon was also associated with the downward mixing of particles into the street canyon from the UBL. The results from this study clearly illustrate the temporal and spatial variability of particle numbers and fluxes in the urban atmosphere.
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