Upper-air Observations Research Articles

A Sea Breeze Study during Ticosonde-NAME 2004 in the Central Pacific of Costa Rica: Observations and Numerical Modeling

Surface and upper air observations and MM5v3 simulations examined the structure and inland penetration of sea breeze (SB) along the Grande de Tárcoles river basin (GTRB), central Pacific, Costa Rica, for two different intensity regimes of the Caribbean Low-Level Jet (CLLJ). Data comprise the period of 1 July to 16 September 2004 from Ticosonde-North American Monsoon Experiment, and a local University of Costa Rica-National Meteorological Institute field campaign. Maximum precipitation occurs between 14:00–17:00 LST, showing a time lag of 2 to 3 h after the temperature maximum, suggesting that local diurnal heating is key to convection. July–August precipitation exhibited a rainfall decrease along GTRB due to the SB dynamical processes interaction with a strong CLLJ. The SB maximum inland incursion was 24 km, with no evidence of its penetration into the Central Valley. The MM5v3 simulations for two convective and boundary layer (BL) schemes captured some SB structure features along the GTRB. Comparison of model results with observed data shows deficiencies in the model representation of the surface flow near coastal regions. Differences may be the result of time lag model’s poor responses to actual early morning BL sea–land temperature gradients. MM5v3 configurations used in this study resulted in biased wind speed simulations.

Total column ozone in New Zealand and in the UK in the 1950s

Abstract. Total column ozone measurements reach back almost a century. Historical column ozone data are important not only for obtaining a long-term perspective of changes of the ozone layer but arguably also as diagnostics of lower-stratospheric or tropopause-level flow in time periods of sparse upper-air observations. With the exception of a few high-quality records such as that from Arosa, Switzerland, ozone science has almost exclusively focused on data since the International Geophysical Year (IGY) in 1957–1958, although earlier series exist. In the early 2000s, we digitised and re-evaluated many pre-IGY series. Here we add a series from Wellington, New Zealand, from 1951 to 1959. We re-evaluated the data from the original observation sheets and performed quality control analysis, and here we present the data. The day-to-day variability can be used to assess the quality of reanalysis products, since the data cover a region and time period with only few upper-air data. Comparison with total column ozone in the reanalyses ERA-PreSAT (which assimilates upper-air data) and 20CRv3 and CERA-20C (which do not assimilate upper-air data) shows high correlations with all three. Although trend quality is doubtful (no calibration information and no intercomparisons are available), combining the record with other available data (including historical data from Australian locations) allows a 70-year perspective of ozone changes over the southern mid-latitudes. The series will be available from the World Ozone and Ultraviolet Data Centre. Finally, we also present a short series from Downham Market, UK, covering November 1950 to October 1951, and publish it with further historical data series that were previously described but not published.

Skill and Potential Economic Value of Forecasts of Ice Accretion on Wind Turbines

AbstractIn this paper, a verification study of the skill and potential economic value of forecasts of ice accretion on wind turbines is presented. The phase of active ice formation on turbine blades has been associated with the strongest wind power production losses in cold climates; however, skillful icing forecasts could permit taking protective measures using anti-icing systems. Coarse- and high-resolution forecasts for the range up to day 3 from global (IFS and GFS) and limited-area (WRF) models are coupled to the Makkonen icing model. Surface and upper-air observations and icing measurements at turbine hub height at two wind farms in central Europe are used for model verification over two winters. Two case studies contrasting a correct and an incorrect forecast highlight the difficulty of correctly predicting individual icing events. A meaningful assessment of model skill is possible only after bias correction of icing-related parameters and selection of model-dependent optimal thresholds for ice growth rate. The skill of bias-corrected forecasts of freezing and humid conditions is virtually identical for all models. Hourly forecasts of active ice accretion generally show limited skill; however, results strongly suggest the superiority of high-resolution WRF forecasts relative to other model variants. Predictions of the occurrence of icing within a period of 6 h are found to have substantially better accuracy. Probabilistic forecasts of icing that are based on gridpoint neighborhood ensembles show slightly higher potential economic value than forecasts that are based on individual gridpoint values, in particular at low cost-loss ratios, that is, when anti-icing measures are comparatively inexpensive.

The development of the “Storm Tracker” and its applications for atmospheric high-resolution upper-air observations

Abstract. In this study, we introduce a newly developed upper-air observational instrument for atmospheric research. The “Storm Tracker” is an ultra-lightweight (about 20 g including battery), multi-channel simultaneous capable radiosonde designed by the Department of Atmospheric Sciences at National Taiwan University. Developed in 2016, the Storm Tracker aims to provide an alternative for observing atmospheric vertical profiles with a high temporal resolution, especially the lower-level atmosphere under severe weather conditions such as extreme thunderstorms and tropical cyclones. Field experiments were conducted as trial runs in Wu-Chi, Taichung, Taiwan, to examine the ability of the Storm Tracker to observe the boundary layer, in addition to the intercomparison between the Storm Tracker and the widely used Vaisala RS41-SGP radiosonde. Among the co-launches of the Storm Tracker and Vaisala RS41 radiosondes, the measurements of pressure, wind speed, and wind direction are highly consistent between the measurements of the Storm Tracker and the Vaisala RS41-SGP. However, a significant daytime warm bias in the Storm Tracker was found due to solar heating. A metal shield specifically for the Storm Tracker was thus installed and showed mitigation for the warm biases and the overall variance. With the much lower costs of the radiosondes and the simultaneous multi-channel receiver, the Storm Tracker system has shown great potential for high-frequency observational needs in atmospheric research.

Use of automatic radiosonde launchers to measure temperature and humidity profiles from the GRUAN perspective

Abstract. In the last two decades, technological progress has not only seen improvements to the quality of atmospheric upper-air observations but also provided the opportunity to design and implement automated systems able to replace measurement procedures typically performed manually. Radiosoundings, which remain one of the primary data sources for weather and climate applications, are still largely performed around the world manually, although increasingly fully automated upper-air observations are used, from urban areas to the remotest locations, which minimize operating costs and challenges in performing radiosounding launches. This analysis presents a first step to demonstrating the reliability of the automatic radiosonde launchers (ARLs) provided by Vaisala, Meteomodem and Meisei. The metadata and datasets collected by a few existing ARLs operated by the Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN) certified or candidate sites (Sodankylä, Payerne, Trappes, Potenza) have been investigated and a comparative analysis of the technical performance (i.e. manual versus ARL) is reported. The performance of ARLs is evaluated as being similar or superior to those achieved with the traditional manual launches in terms of percentage of successful launches, balloon burst and ascent speed. For both temperature and relative humidity, the ground-check comparisons showed a negative bias of a few tenths of a degree and % RH, respectively. Two datasets of parallel soundings between manual and ARL-based measurements, using identical sonde models, provided by Sodankylä and Faa'a stations, showed mean differences between the ARL and manual launches smaller than ±0.2 K up to 10 hPa for the temperature profiles. For relative humidity, differences were smaller than 1 % RH for the Sodankylä dataset up to 300 hPa, while they were smaller than 0.7 % RH for Faa'a station. Finally, the observation-minus-background (O–B) mean and root mean square (rms) statistics for German RS92 and RS41 stations, which operate a mix of manual and ARL launch protocols, calculated using the European Centre for Medium-Range Weather Forecasts (ECMWF) forecast model, are very similar, although RS41 shows larger rms(O–B) differences for ARL stations, in particular for temperature and wind. A discussion of the potential next steps proposed by GRUAN community and other parties is provided, with the aim to lay the basis for the elaboration of a strategy to fully demonstrate the value of ARLs and guarantee that the provided products are traceable and suitable for the creation of GRUAN data products.

A multi-sensor and modeling analysis of a severe convective storm in Lake Maggiore area (northwestern Italy)

The analysis of a severe convective storm, occurred in northwestern Italy during late summer 2012, is presented here. The event was characterized by heavy precipitation, hail and intense wind gusts, causing injuries and damages to trees, buildings and infrastructures.The description of the case study draws upon a wide palette of observational data. Surface and upper-air observations helped characterize the event, emphasizing the rapid changes in the meteorological parameters in the study area; satellite data highlights the presence of deep moist convection, associated with strong updrafts; Doppler radar allows the identification of the main features of the event in terms of storm-motion, hail detection/probability and the possible presence of a mesocyclone.A high-resolution (3 km inner grid spacing) simulation with the WRF (Weather Research and Forecasting) model was performed to study the atmospheric conditions conducive to convection, as well as to estimate the main instability parameters. The main features of the storm were well reproduced with WRF; furthermore, the high values of the simulated instability parameters denote the presence of favourable conditions for severe convection.The analysis of this event shows that supercells can develop also in a pre-alpine environment, characterized by a complex orography, in particular in the sub-regions where the local morphology creates conditions favourable for severe weather development.

The relationship between low-level cloud amount and its proxies over the globe by cloud type

Abstract. We extend upon previous work to examine the relationship between low-level cloud amount (LCA) and various proxies for LCA – estimated low-level cloud fraction (ELF), lower tropospheric stability (LTS), and estimated inversion strength (EIS) – by low-level cloud type (CL) over the globe using individual surface and upper-air observations. Individual CL has its own distinct environmental structure, and therefore our extended analysis by CL can provide insights into the strengths and weaknesses of various proxies and help to improve them. Overall, ELF performs better than LTS and EIS in diagnosing the variations in LCA among various CLs, indicating that a previously identified superior performance of ELF compared to LTS and EIS as a global proxy for LCA comes from its realistic correlations with various CLs rather than with a specific CL. However, ELF, LTS, and EIS have a problem in diagnosing the changes in LCA when noCL (no low-level cloud) is reported and also when Cu (cumulus) is reported over deserts where background stratus does not exist. This incorrect diagnosis of noCL as a cloudy condition is more clearly seen in the analysis of individual CL frequencies binned by proxy values. If noCL is excluded, ELF, LTS, and EIS have good inter-CL correlations with the amount when present (AWP) of individual CLs. In the future, an advanced ELF needs to be formulated to deal with the decrease in LCA when the inversion base height is lower than the lifting condensation level to diagnose cumulus updraft fraction, as well as the amount of stratiform clouds and detrained cumulus, and to parameterize the scale height as a function of appropriate environmental variables.

Real-time NWP simulations over north-Africa and Morocco using the Unified Environmental Modeling System (UEMS)

Weather forecasting is a very challenging task due to dynamical and nonlinear structures associated to the atmosphere. In fact, the atmosphere is described as a chaotic system; this means that small changes at a point in time can lead to large changes later in the forecast period. Despite its complexity, numerical weather prediction models (NWP) are good tools that allow us to make a big step forward in weather forecasting because of the huge increases in computing power and better physical modelling schemes available today. In this work we summarize the achieved tasks of the implementation of a real-time NWP simulation using the Unified Environmental Modeling System (UEMS) over north-Africa and Morocco. Technical and operational characteristics of our real-time weather forecast system will be described, and a case study will be illustrated on a real meteorological situation. The validation of our model is performed based on comparisons against surface and upper air observations, using the verification package of the Model Evaluation Tools (MET).

The Effect of an Active Phase of the Madden-Julian Oscillation on Surface Winds over the Western Coast of Sumatra Island

This study examined the effect of an active phase of the Madden-Julian Oscillation (MJO) on surface winds over the western coast of Sumatra Island using surface meteorological observations, meteorological radar observations, and balloon sounding data obtained from the Years of the Maritime Continent (YMC) Sumatra 2017 field campaign. Wind gusts (sudden and large increases in surface wind speed with durations of several to tens of minutes; squall) were observed frequently at Bengkulu from late November to early December 2017 during a local active phase of the MJO. The wind gusts occurred simultaneously with heavy precipitation when the eastward propagating convection from the Indian Ocean moved over the observation site. Upper air observations showed strong northwesterly winds in the lower troposphere in the 1,000–4,000 m layer. The surface wind gusts extended from the surface up to an elevation of 560 m, with the highest wind speed occurring approximately 300 m above the ground. Small changes in surface air pressure were observed during the wind gusts. The results suggested that momentum transfer from the upper atmosphere by downdrafts was the main cause of the surface wind gusts on the western coast of Sumatra Island during an active phase of the MJO.

Downslope Winds and Dust Storms in the Salton Basin

Abstract The Salton basin is a closed, subsea level basin located in extreme southeastern California. At the center of the basin lies the Salton Sea, the state’s largest inland lake, which is surrounded by a desert landscape characterized by paleo lakebed surfaces, dry washes, alluvial fans, and interdunes. Dust storms are common occurrence in this region. However, despite the regularity of dust outbreaks here, little is known about the meteorological processes responsible for these storms. Here I use observations and output from reanalysis to elucidate the meteorological controls on dust emission events in the Salton basin during 2015–18. Analysis of surface and upper-air observations, satellite data, and reanalysis, suggest that the largest dust storms in the region are associated with an upper-level low centered near the coastline of western Canada, which directs a zonal low-level jet over the region. Flow blocking by a coastal mountain range results in isentropic drawdown of air in the lee of these mountains. Once surface warming at the floor of the Salton basin is sufficient such that the density of the descending air is greater than that of the ambient air at the surface, the downslope windstorm reaches the desert floor and initiates dust emission. This process may also be accompanied by a downwind propagating hydraulic jump. These processes appear to be similar to those responsible for the strongest dust events in the Owens Valley, and may represent the main mechanisms for emission from other closed basins.

Comparison of Regional Atmospheric Model Forecasts under Different Initial and Boundary Conditions

The results of forecasts of the WRF-ARW numerical mesoscale model with two sets of initial and boundary conditions are presented. The first set comprises the forecasts of the GFS global model (USA), and the second set, the forecasts of the SL-AV global model (Russia). The quality of the WRF-ARW forecasts is assessed by their comparison with the data of surface and upper-air meteorological observations for the European part of Russia in winter and summer. It is shown that the 72-hour forecast results are close to the results based on the GFS data if the Russian global model data are used as initial and boundary conditions.

Heuristic estimation of low-level cloud fraction over the globe based on a decoupling parameterization

Abstract. Based on the decoupling parameterization of the cloud-topped planetary boundary layer, a simple equation is derived to compute the inversion height. In combination with the lifting condensation level and the amount of water vapor in near-surface air, we propose a low-level cloud suppression parameter (LCS) and estimated low-level cloud fraction (ELF), as new proxies for the analysis of the spatiotemporal variation of the global low-level cloud amount (LCA). Individual surface and upper-air observations are used to compute LCS and ELF as well as lower-tropospheric stability (LTS), estimated inversion strength (EIS), and estimated cloud-top entrainment index (ECTEI), three proxies for LCA that have been widely used in previous studies. The spatiotemporal correlations between these proxies and surface-observed LCA were analyzed. Over the subtropical marine stratocumulus deck, both LTS and EIS diagnose seasonal–interannual variations of LCA well. However, their use as a global proxy for LCA is limited due to their weaker and inconsistent relationship with LCA over land. EIS is anti-correlated with the decoupling strength more strongly than it is correlated with the inversion strength. Compared with LTS and EIS, ELF and LCS better diagnose temporal variations of LCA, not only over the marine stratocumulus deck but also in other regions. However, all proxies have a weakness in diagnosing interannual variations of LCA in several subtropical stratocumulus decks. In the analysis using all data, ELF achieves the best performance in diagnosing spatiotemporal variation of LCA, explaining about 60 % of the spatial–seasonal–interannual variance of the seasonal LCA over the globe, which is a much larger percentage than those explained by LTS (2 %) and EIS (4 %). Our study implies that accurate prediction of inversion base height and lifting condensation level is a key factor necessary for successful simulation of global low-level clouds in general circulation models (GCMs). Strong spatiotemporal correlation between ELF (or LCS) and LCA identified in our study can be used to evaluate the performance of GCMs, identify the source of inaccurate simulation of LCA, and better understand climate sensitivity.

Estimating the Frequency of Sudden Stratospheric Warming Events From Surface Observations of the North Atlantic Oscillation

AbstractSudden stratospheric warming (SSW) events can exhibit long‐lasting surface impacts that promise improvements in medium‐range to seasonal predictability. Their surface impact is dominated by the negative phase of the North Atlantic Oscillation (NAO). Hence, the question arises if stratospheric variability, and in particular the frequency of SSW events, can in turn be estimated from surface NAO conditions. This is especially relevant for the period before frequent upper air observations became available, while daily surface observations of the NAO date back to 1850. The surface impact is here quantified by NAO characteristics that are commonly observed after SSW events: a switch from a positive to a negative NAO and an extended persistence of the negative NAO, termed NAO events. Two thirds of SSW events are found to be followed by either a persistence or switch NAO event, and a quarter of SSW events are followed by both. On the other hand, less than 25% of winter surface NAO events are preceded by a SSW event. Based on these findings, an index purely based on surface NAO observations is derived that estimates SSW frequency for the satellite era and extends it back to 1850, indicating that decadal stratospheric variability was present for the entire time series, with no significant trend. The minimum in SSW frequency in the 1990s is found to be coincident with the longest absence of NAO events since 1850, indicating that the early 1990s may constitute the longest absence of SSW events for the 150‐year record.

Modeling Air Dispersion of Pollutants Emitted from the Daura Oil Refinery, Baghdad- Iraq using the CALPUFF Modeling System

The CALPUFF atmospheric transport model was used to estimate ambient air concentrations of SO2, CO, NO2, and PM2.5, in a 256 km2 region surrounding the Daura oil refinery in Baghdad, Iraq during a six month period in the summer for 2013 and the winter of 2014. The CALPUFF modeling system includes a meteorological processor (CALMET), a Lagrangian puff atmospheric transport model (CALPUFF), and a post processor (CALPOST). Source term and meteorological data, including surface and upper air observations, were pre-processed and formatted for CALMET and CALPUFF using FORTRAN programs. Monthly emission rates and stack parameters for twelve stack sources were included in the model. Winds out of the northwest predominated, followed by winds out of the north and the west. The urban regions with the highest pollutant concentrations in the study domain were the Daura Express Highway located south and southeast of the facility, and the refinery employee residences located west of the facility. These areas were closest to the Daura oil refinery. Predicted pollutant concentrations showed that SO2 and CO were higher than NO2 and PM2.5, for the study period because emission rates of SO2 and CO were greater than NO2 and PM2.5. Monthly dispersion patterns were similar among the pollutants and exhibit plumes in the predominant wind direction. Winter generally had the highest predicted pollutant concentrations compared to the summer months.

Improved 4-DVar Simulation of Indian Ocean Tropical Cyclones Using a Regional Model

The performance of the 4-D variational (4-DVar) data assimilation system over the 3-D variational assimilation system is investigated for the simulation of tropical cyclones (TCs), using the weather research and forecasting model. Two TCs (cyclone Thane and cyclone Hudhud) that formed over the North Indian Ocean have been considered in this paper. Surface and upper air observations from Global Telecommunications Systems in combination with ocean surface winds and satellite derived atmospheric motion vectors are assimilated cyclically at an interval of 6 h. The analysis is then integrated for a period of 72 h in the free forecast mode for both the assimilation runs. The 4-DVar run results for cyclone Thane shows significant impact on rainfall forecast, with an average equitable threat score (ETS) twice that of 3-DVar run, while the 4-DVar run for cyclone Hudhud shows a little improvement in ETS. The average initial error in mean sea level pressure for analysis fields for 4-DVar run is found to about half of the 3-DVar counterpart for the case of cyclone Hudhud. Improvement in 4-DVar simulation of maximum surface wind speed is found to be 7% and 14% for cyclone Thane and Hudhud, respectively. Also, the 4-DVar run for cyclone Thane resulted in an average reduction of 10% in track error simulation, while the same for cyclone Hudhud revealed a little improvement.

Effect of sea breeze propagation on the urban boundary layer of the metropolitan region of Sao Paulo, Brazil

Thermally driven circulations over urban areas, such as sea, lake, and land breezes and mountain-valley and urban heat island (UHI) circulations, strongly determine local weather and air quality conditions over highly populated areas. This study investigates the influence of sea breeze (SB) propagation on the development of the urban boundary layer (UBL) in the Metropolitan Region of Sao Paulo (MRSP), Brazil, an urban area with complex topography. This investigation is undertaken observationally by analyzing surface and upper air observations conducted in 2013 during the MCITY BRAZIL Project field campaigns and is conducted numerically by performing a set of Weather Research and Forecasting (WRF) simulations. The observational analysis highlights two SB events in the MRSP, one in February (austral summer) and the other in August (winter). In both seasons, the passage of the SB front disrupts the convective growth of the UBL and establishes a thermal internal boundary layer, thereby reducing the UBL height. The cooling also momentarily disrupts the UHI circulation. The results indicate that topography enhances SB propagation because it helps the marine air to go up the MRSP coastal escarpment and to reach the plateau while forcing adiabatic cooling of this air, intensifying the thermal gradient between the southern part of the plateau and the urban area. The UHI further increases the thermal gradient (from 0.5 K to 2 K in summer and 1 to 2.5 K in winter), accelerating the SB propagation. Synoptic conditions determine whether the SB front reaches the urban area and also may displace the convergence center of the UHI circulation.

The Thermodynamic Structure of Arctic Coastal Fog Occurring During the Melt Season over East Greenland

An automated method to classify Arctic fog into distinct thermodynamic profiles using historic in-situ surface and upper-air observations is presented. This classification is applied to low-resolution Integrated Global Radiosonde Archive (IGRA) soundings and high-resolution Arctic Summer Cloud Ocean Study (ASCOS) soundings in low- and high-Arctic coastal and pack-ice environments. Results allow investigation of fog macrophysical properties and processes in coastal East Greenland during melt seasons 1980–2012. Integrated with fog observations from three synoptic weather stations, 422 IGRA soundings are classified into six fog thermodynamic types based on surface saturation ratio, type of temperature inversion, fog-top height relative to inversion-base height and stability using the virtual potential temperature gradient. Between 65–80% of fog observations occur with a low-level inversion, and statically neutral or unstable surface layers occur frequently. Thermodynamic classification is sensitive to the assigned dew-point depression threshold, but categorization is robust. Despite differences in the vertical resolution of radiosonde observations, IGRA and ASCOS soundings yield the same six fog classes, with fog-class distribution varying with latitude and environmental conditions. High-Arctic fog frequently resides within an elevated inversion layer, whereas low-Arctic fog is more often restricted to the mixed layer. Using supplementary time-lapse images, ASCOS microwave radiometer retrievals and airmass back-trajectories, we hypothesize that the thermodynamic classes represent different stages of advection fog formation, development, and dissipation, including stratus-base lowering and fog lifting. This automated extraction of thermodynamic boundary-layer and inversion structure can be applied to radiosonde observations worldwide to better evaluate fog conditions that affect transportation and lead to improvements in numerical models.

On the Use of Radiosondes in Freezing Precipitation

AbstractRadiosonde observations are used the world over to provide critical upper-air observations of the lower atmosphere. These observations are susceptible to errors that must be mitigated or avoided when identified. One source of error not previously addressed is radiosonde icing in winter storms, which can affect forecasts, warning operations, and model initialization. Under certain conditions, ice can form on the radiosonde, leading to decreased response times and incorrect readings. Evidence of radiosonde icing is presented for a winter storm event in Norman, Oklahoma, on 24 November 2013. A special sounding that included a particle imager probe and a GoPro camera was flown into the system producing ice pellets. While the iced-over temperature sensor showed no evidence of an elevated melting layer (ML), complementary Particle Size, Image, and Velocity (PASIV) probe and polarimetric radar observations provide clear evidence that an ML was indeed present. Radiosonde icing can occur while passing through a layer of supercooled drops, such as frequently found in a subfreezing layer that often lies below the ML in winter storms. Events that have warmer/deeper MLs would likely melt any ice present off the radiosonde, minimizing radiosonde icing and allowing the ML to be detected. This paper discusses the hypothesis that the absence of an ML in the radiosonde data presented here is more likely to occur in winter storms that produce ice pellets, which tend to have cooler/shallower MLs. Where sounding data do appear to be compromised by icing, polarimetric radar data might be used to identify MLs for nowcasting purposes and numerical model initialization.

Assessing the Impact of Surface and Upper-Air Observations on the Forecast Skill of the ACCESS Numerical Weather Prediction Model over Australia

The impact of the Australian Bureau of Meteorology’s in situ observations (land and sea surface observations, upper air observations by radiosondes, pilot balloons, wind profilers, and aircraft observations) on the short-term forecast skill provided by the ACCESS (Australian Community Climate and Earth-System Simulator) global numerical weather prediction (NWP) system is evaluated using an adjoint-based method. This technique makes use of the adjoint perturbation forecast model utilized within the 4D-Var assimilation system, and is able to calculate the individual impact of each assimilated observation in a cycling NWP system. The results obtained show that synoptic observations account for about 60% of the 24-h forecast error reduction, with the remainder accounted for by aircraft (12.8%), radiosondes (10.5%), wind profilers (3.9%), pilot balloons (2.8%), buoys (1.7%) and ships (1.2%). In contrast, the largest impact per observation is from buoys and aircraft. Overall, all observation types have a positive impact on the 24-h forecast skill. Such results help to support the decision-making process regarding the evolution of the observing network, particularly at the national level. Consequently, this 4D-Var-based approach has great potential as a tool to assist the design and running of an efficient and effective observing network.

Validation and deployment of the first Lidar based weather observation network in New York State: The NYS MesoNet Project

The number and quality of atmospheric observations used by meteorologists and operational forecasters are increasing year after year, and yet, consistent improvements in forecast skill remains a challenge. While contributing factors involving these challenges have been identified, including the difficulty in accurately establishing initial conditions, improving the observations at regional and local scales is necessary for accurate depiction of the atmospheric boundary layer (below 2km), particularly the wind profile, in high resolution numerical models. Above the uncertainty of weather forecasts, the goal is also to improve the detection of severe and extreme weather events (severe thunderstorms, tornadoes and other mesoscale phenomena) that can adversely affect life, property and commerce, primarily in densely populated urban centers. This paper will describe the New York State Mesonet that is being deployed in the state of New York, USA. It is composed of 126 stations including 17 profiler sites. These sites will acquire continuous upper air observations through the combination of WINDCUBE Lidars and microwave radiometers. These stations will provide temperature, relative humidity & “3D” wind profile measurements through and above the planetary boundary layer (PBL) and will retrieve derived atmospheric quantities such as the PBL height, cloud base, momentum fluxes, and aerosol & cloud optical properties. The different modes and configurations that will be used for the Lidars are discussed. The performances in terms of data availability and wind accuracy and precision are evaluated. Several profiles with specific wind and aerosol features are presented to illustrate the benefits of the use of Coherent Doppler Lidars to monitor accurately the PBL.