High-resolution Radiosonde Data Research Articles

Cold Surge Impacts on the Structure, Energy Budget, and Turbulence of the South China Sea Boundary Layer

Abstract Episodic cold surges in the East Asia winter monsoon can penetrate deep into the South China Sea (SCS), enhance consequent tropical rainfall, and further strengthen the East Asia meridional overturning circulation. These cold surges can promote strong surface fluxes and lead to a deeper marine boundary layer (MBL). However, there is a lack of boundary layer studies over the SCS, unlike many other well-studied regions such as the north Atlantic Ocean and the central-eastern Pacific Ocean. In this study, we use high resolution radiosonde data of temperature and humidity profiles over Dongsha Island (116.69E, 20.70N) to identify the inversion layer, mixed layer, cloud base, cloud top, and factors controlling low cloud cover for the period of December-January-February from 2010 to 2020. We perform an energy budget analysis with ERA-5 meteorological variables and surface fluxes. Here we show a strong turbulent flux convergence of both heat and moisture within the SCS MBL during cold surges, which leads to a lifting of the mixed layer to ~1.0 km and inversion layer to ~2.0 km and associated cloud development over Dongsha Island. The cold and dry horizontal advection is balanced by this vertical turbulent flux convergence in the energy budget. Overall, cold surges over the SCS enhance lower branch of winter monsoon meridional overturning circulation with stronger inversion and higher low cloud covers.

An ensemble method for improving the estimation of planetary boundary layer height from radiosonde data

Abstract. The planetary boundary layer (PBL) height (PBLH) is an important parameter for weather, climate, and air quality models. Radiosonde is one of the most commonly used instruments for PBLH determination and is generally accepted as a standard for other methods. However, mainstream approaches for the estimation of PBLH from radiosonde present some uncertainties and even show disadvantages under some circumstances, and the results need to be visually verified, especially during the transition period of different PBL regimes. To avoid the limitations of individual methods and provide a benchmark estimation of PBLH, we propose an ensemble method based on high-resolution radiosonde data collected in Beijing in 2017. Seven existing methods including four gradient-based methods are combined along with statistical modification. The ensemble method is verified at 08:00, 14:00, and 20:00 Beijing time (BJT = UTC+8), respectively. The overestimation of PBLH can be effectively eliminated by setting thresholds for gradient-based methods, and the inconsistency between individual methods can be reduced by clustering. Based on the statistics of a 1-year observational analysis, the effectiveness (E) of the ensemble method reaches up to 62.6 %, an increase of 6.5 %–53.0 % compared to the existing methods. Nevertheless, the ensemble method suffers to some extent from uncertainties caused by the consistent overestimation of PBLH, the profiles with a multi-layer structure, and the intermittent turbulence in the stable boundary layer (SBL). Finally, this method has been applied to characterize the diurnal and seasonal variations of different PBL regimes. Particularly, the average convective boundary layer (CBL) height is found to be the highest in summer, and the SBL is lowest in summer with about 200 m. The average PBLH at the transition stage lies around 1100 m except in winter. These findings imply that the ensemble method is reliable and effective.

The Gravity Wave Activity during Two Recent QBO Disruptions Revealed by U.S. High-Resolution Radiosonde Data

The westerly phase of the stratospheric Quasi-Biennial Oscillation (QBO) was unprecedentedly interrupted by an easterly jet at around 22 km during boreal wintertime in 2015/2016 and 2019/2020. Many studies have investigated the role of planetary waves during these disruptions. However, the behavior of gravity waves (GWs) during these disruptions is still unclear. In this paper, we investigated the characteristics of stratospheric GWs during QBO disruptions by analyzing the U.S. high-resolution radiosonde data from 1998 to 2021 from three equatorial stations. The disruptions were separated into three stages: the westerly zonal wind decreasing stage, the easterly zonal wind developing stage, and the westerly zonal wind recovery stage. Notably, the tropical stratospheric GWs’ total energy densities were enhanced during all three stages of both events compared to those in typical years. The low-tropospheric convection, the middle-tropospheric jet, and the low-stratospheric vertical wind shear were statistically associated with the stratospheric GW variations. A quantitative analysis further indicated that the low-tropospheric convection activity, tropospheric jets, and wind shears in the lower stratosphere could well explain the variations in the stratospheric GWs in the westerly zonal wind decreasing and easterly zonal wind developing stages by applying a partial least squares regress analysis.

Extreme variability of the tropical tropopause over the Indian monsoon region

The extreme variability of the tropical tropopause may serve as an important factor in understanding the critical conditions of dynamical and radiative coupling between the troposphere and stratosphere. The extreme variability of the cold point tropopause (CPT) temperature (TCPT) and height (HCPT) are examined over a tropical station, Gadanki (13.45° N, 79.2° E), using high-resolution radiosonde data during 2006–2014. We identified the extremely cold, warm, high, and low tropopauses. The extremely cold (warm) tropopause is defined as the TCPT lesser (greater) than the lower (upper) limit of the two standard deviations of its climatological monthly mean. While the extremely high (low) tropopause is defined as the HCPT greater (lesser) than the upper (lower) limit of the two standard deviations of its climatological monthly mean. In total, 161 cases comprising extremely cold (52), warm (30), high (57), and low (22) are observed. The extremely cold (187.2 ± 1.60 K, 17.3 ± 0.52 km), warm (194.2 ± 1.78 K, 16.9 ± 0.89 km), high (191.7 ± 1.78 K, 18.2 ± 0.55 km), and low (191.8 ± 2.11 K, 16.2 ± 0.38 km) tropopauses occur without preference of season. However, these extreme tropopause cases occur independently and show distinct thermal structures. The thermal structures of the extremely cold tropopause cases are often sharper, whereas the extremely warm, high, and low tropopause cases are broader. Water vapor and ozone concentrations are found to be high for the extremely warm tropopause and low for the extremely cold tropopause. Under the shallow convection, extreme temperature profiles, in general, show prominent warming between 8 and 14 km while anomalous cooling (warming) just below (above) the CPT. Plausible mechanisms responsible for extreme tropopause variabilities such as deep convection, equatorial wave propagation, transports of water vapor and ozone, and potential vorticity intrusions are examined.

Elucidating the impact of high- and low-pressure systems on temperature inversion from nine years of radiosonde observations in Beijing

Temperature inversion (TI) has long been recognized to play an important role in air quality and convection initiation, mainly through modulating the dynamic and thermodynamic processes of planetary boundary layer (PBL). Yet, our knowledge remains poor regarding the relationship between TI and the synoptic systems. Here we use nine years (2011–2019) of high-resolution radiosonde data from the Beijing site to quantify the impact of TI on the dynamic and thermodynamic conditions associated with the activities of synoptic systems. The monthly, seasonal and diurnal changes of the TI occurrence frequencies are first analyzed, and the surface-based inversions (SBIs) are found more related to the surface properties, whereas elevated inversions (EIs) are potentially more influenced by thermodynamic and dynamic characteristics of the atmosphere. A novel method based on the threshold of seasonal averaged sea level pressure for identifying the centers of high-pressure system (HPS) and low-pressure system (LPS) is developed. Statistical analyses show that the pressure gradients are stronger in the presence of TI, when HPS or LPS centers approach the observational site of interest from the northwest. The pressure difference becomes larger between the center and the site when the HPS or LPS center locates farther. Height-resolved zonal and meridional temperature advection and wind anomalies are further investigated, showing that the EIs are possibly related to the downslope intrusion of cold air under the control of HPS and to the heat transportation under the control of LPS over the mountain slopes. The TI-favored temperature advection brought by the prevailing wind of the synoptic systems, aided by topographic uplifting, may also reinforce the occurrence of EI.

Case Analysis of Turbulence From High-Resolution Sounding Data in Northwest China

This study calculated the Thorpe scale, thickness of turbulent layer, turbulent kinetic energy dissipation rate, and turbulent diffusion coefficient based on the Thorpe method using a set of near-space high-resolution radiosonde data in northwest China, and a case study was conducted to analyze the large-scale turbulent layer in the middle stratosphere. The results showed that the most turbulent layers exist near from the middle and upper troposphere to the tropopause region, accounting for 44.0% of the total turbulence, and the largest Thorpe scale and thickness of turbulent layer also appear in this altitude range. In addition, affected by the large-scale turbulence near the tropopause, the calculated turbulent energy dissipation rate and diffusion coefficient also have maximum values at this altitude, which are 0.003 m2s−3 and 6.94 m2s−1, respectively. By analyzing the meteorological elements, it is found that there is an obvious correlation between precipitation and large-scale turbulence in the stratosphere. When the precipitation occurs, the corresponding two sets of radiosondes detected larger-scale turbulence layers in the middle stratosphere.

Thermodynamic structure of monsoon boundary layer over the west coast of India

The study investigates thermodynamic structure of the atmospheric boundary layer (ABL) over the west coast of India during the southwest monsoon season. Radiosonde profiles at 00 UTC (0530 IST) are utilised for three stations, namely Thiruvananthapuram (TVM), Mangalore (MNG) and Mumbai (MUM) to represent south, central and north parts of the west coast, respectively. The high vertical resolution radiosonde data were collected from India Meteorological Department (IMD) for the period 1st May to 31st October 2018. Variations in the thermodynamic parameters associated with the monsoon and active and weak surges are examined. The active and weak monsoon conditions are identified using the values of OLR (outgoing longwave radiation) and rainfall in the respective stations. The study delineates interesting dynamic and thermodynamic features over the region. The thermodynamic parameters possess remarkable variations associated with the approach of the monsoon surges. TVM is characterised by absolutely stable or conditionally neutral (conditionally unstable) layer above a shallow conditionally unstable layer over the ground during the active (weak) monsoon situations; however, over MNG and MUM, ABL is conditionally unstable during both active and weak situations. Stable atmosphere is expected to cause stratiform clouds under favourable dynamic factors, whereas unstable atmosphere can aid vertical development of clouds and this can be attributed to the vertical shear of zonal wind. Zonal wind has a sharp increase from the ground to above ABL (~ 1200 m) in TVM; however, it is in the lower levels of ABL over MNG and MUM. In MUM, strong zonal wind is observed during the active (>20 m s−1) and weak (>12 m s−1) situations that causes intense mixing and maximum ABL height. The enhanced monsoon activity in MUM (MNG) is mainly associated with the active phase of the monsoon intraseasonal oscillation (active phase of the monsoon intraseasonal oscillation and strengthening of low level zonal wind), whereas in TVM it is mainly associated with the strengthening of low level zonal wind. The ABL heights are elevated during weak monsoon conditions due to convective turbulence added to the mechanical turbulence associated with the strong wind during the season.

Characteristics of low-level temperature inversions over the Arctic Ocean during the CHINARE 2018 campaign in summer

Across the Arctic Ocean, the semi-permanent sea-ice layer insulates the atmosphere from the Arctic Ocean, thereby influencing the lower boundary conditions of the atmosphere in this region. The presence of a temperature inversion predominantly characterizes the Arctic lower troposphere throughout the year. The 9th Chinese National Arctic Research Expedition took place in the Pacific Sectors of the Arctic Ocean from July to September 2018, gathering high-resolution radiosonde data to provide a detailed structure of the low-level temperature inversion (LLI) over the summer months. Statistical analyses showed that LLIs occurred most frequently below 500m and were generally weaker and shallower than those occurring during the winter months. Low-level inversions are influenced by both local meteorology and large scale synoptic conditions. The continual presence of low-level clouds or fog tends to lift the inversion layer at the local scale, transferring it from a surface-based inversion (SBI) to an elevated inversion (EI). By contrast, SBIs were found to dominate over regions of melting sea-ice. Regimes, where the cloud top penetrated the inversion base were more frequently observed than cloud capped by inversion regimes. Inversions tended to be deeper, stronger, and with a lower base during cloud top penetrating inversion base regimes. At the synoptical scale, the intense poleward intrusions of warm air brought moist air to the top of low-level inversions, creating a robust thermal stratification between layers and promoting extensive and frequency occurrences of low cloud/fog. Moreover, the polar high contributed to establishing a multilayer inversion structure at relatively high altitudes by subsidence. These findings contribute to an improving understanding of low-level vertical temperature structures and their influence on a rapidly warming Arctic.

Characteristics of temperature inversion from radiosonde measurements in the Western Ghats region

The characteristics of temperature inversion (TI) are believed to be dependent on topographical features and synoptic regime. Western Ghats (WGs) mountains located in the west coast of India have a complex topography, and the TI features for this region remain unknown due to the complexity and non-availability of observational datasets. This study investigates TI characteristics in the troposphere using high-resolution radiosonde data (2012–2015). The radiosonde measurements are collected at Mahabaleshwar (17.92°N, 73.6°E, ~1.4 km above mean sea level, AMSL), a high-altitude site in the WGs. The characteristics of TI in terms of height, depth, and strength (i.e., temperature difference between base and top of the inversion layer) are studied. The results showed that TI occurs in all seasons, however, their frequency differs. Winter (Dec.-Feb.) shows the maximum number of inversions followed by pre-monsoon (Mar.-May), post-monsoon (Oct.-Nov.), and monsoon (Jun.-Sep.). In winter, the depth of inversion is higher; however, the inversion strength is weaker as compared to other seasons. The TI strength is always below 5 K. Apart from surface-based inversions, elevated and upper-tropospheric inversions are also observed. Vertical and horizontal wind shear profiles along with ERA-5 data were analyzed to examine the plausible mechanism for TI to occur.

On the association between characteristics of the atmospheric boundary layer and air pollution concentrations

Air pollution in the lower atmosphere is a global concern. Characteristics of the planetary boundary layer (PBL) are considered important determinants of the dispersion and the concentrations of pollutants. This work explores the association between characteristics of the PBL and corresponding air pollution data, separately for different PBL states. Five years (2014–2018) of twice daily (01:30 and 13:30 local time) high resolution radiosonde data were used to estimate the convective and stable boundary layer heights (CBL and SBL, respectively), and the temperature lapse rate, in Bet Dagan, Israel. In 23% of the nights, mostly cloudy ones, no indication for an SBL was found but a clear top of a ground–based residual layer (RBL) was detected. The concentrations of NO, NO2, NOx and PM2.5 were negatively correlated with the heights of the CBL and RBL but positively correlated with the SBL height. Their association with the lapse rate was always negative, weak in daytime (CBL) but very strong during the night (SBL and RBL). The associations with the O3 concentrations were opposite in sign to those with the primary pollutants. The PBL height using the bulk Richardson number method was most strongly associated with the CBL and RBL concentrations but we found it unsuitable for estimating the height of the SBL. Our results demonstrate the importance of accounting for the different states of the PBL. In particular, they suggest that during SBL conditions, the common practice of using the PBL volume as a determinant of pollutant concentrations might not be appropriate.

Analysis and Simulation of the Stratospheric Quasi-zero Wind Layer over Korla, Xinjiang Province, China

The stratospheric quasi-zero wind layer (QZWL) is a transition region with low zonal wind speeds in the lower stratosphere at an altitude of ~20 km. The zonal wind direction above the QZWL layer is opposite to that below the QZWL layer and the north–south wind component is small. The atmospheric wind field near the stratospheric QZWL is an important factor affecting the flight altitude and dynamic control of stratospheric airships. It is therefore necessary to study the stratospheric QZWL to provide better environmental information for these aircraft. High-resolution radiosonde data were used to analyze the characteristics of the stratospheric QZWL over Korla, Xinjiang Province, China. A weak wind layer in which the wind direction suddenly reversed from westerly to easterly was observed at ~20 km in the lower stratosphere, characteristic of the stratospheric QZWL. The Weather Research and Forecasting model was used to simulate the profiles of the horizontal wind speed and direction over Korla. The forcing effect of each diagnostic term in the equation on the zonal wind speed was analyzed. The results showed that the advection term was the dominant factor forcing the zonal wind speed. The wave term had a secondary forcing role, although the forcing effect of the wave term on the zonal wind speed was significant in some regions.

On the fine vertical structure of the low troposphere over the coastal margins of East Antarctica

Abstract. In this study, 8 years of high-resolution radiosonde data at nine Antarctic stations are analysed to provide the first large-scale characterization of the fine vertical structure of the low troposphere up to 3 km altitude over the coastal margins of East Antarctica. Radiosonde data show a large spatial variability of wind, temperature and humidity profiles, with different features between stations in katabatic regions (e.g., Dumont d'Urville and Mawson stations), stations over two ice shelves (Neumayer and Halley stations) and regions with complex orography (e.g., McMurdo). At the Dumont d'Urville, Mawson and Davis stations, the yearly median wind speed profiles exhibit a clear low-level katabatic jet. During precipitation events, the low-level flow generally remains of continental origin and its speed is even reinforced due to the increase in the continent–ocean pressure gradient. Meanwhile, the relative humidity profiles show a dry low troposphere, suggesting the occurrence of low-level sublimation of precipitation in katabatic regions but such a phenomenon does not appreciably occur over the ice shelves near Halley and Neumayer. Although ERA-Interim and ERA5 reanalyses assimilate radiosoundings at most stations considered here, substantial – and sometimes large – low-level wind and humidity biases are revealed but ERA5 shows overall better performance. A free simulation with the regional polar version of the Weather Research and Forecasting model (Polar WRF) (at a 35 km resolution) over the entire continent shows too-strong and too-shallow near-surface jets in katabatic regions especially in winter. This may be a consequence of an underestimated coastal cold air bump and associated sea–continent pressure gradient force due to the coarse 35 km resolution of the Polar WRF simulation. Beyond documenting the vertical structure of the low troposphere over coastal East Antarctica, this study gives insights into the reliability and accuracy of two major reanalysis products in this region on the Earth. The paper further underlines the difficulty of modeling the low-level flow over the margins of the ice sheet with a state-of-the-art atmospheric model.

Radio refractivity gradients in the lowest [formula omitted] of the atmosphere over Lagos, Nigeria in the rainy-harmattan transition phase

Radio engineers and researchers in conjunction with the International Telecommunication Union (ITU) have established the pivotal role of radio refractivity to the propagation of electromagnetic energy in the troposphere. In particular, the refractivity gradient statistics for the lowest 100m in the troposphere are used to determine the probability of occurrence of anomalous propagation conditions known as ducting. The major challenge to characterising the propagation condition over any environment is accessing the data of the lowest boundary layer of the atmosphere, which is highly dynamic and turbulent in evolution. High resolution radiosonde data from the Nigerian Meteorological Agency (NiMet) were used for a synoptic study of the rain-harmattan transition phase. The rain-harmattan transition phase marks the onset of the dry season due to the movement of the intertropical convergence zone interplay between (north-easterly and south-westerly) trade winds and monsoonal circulation. The lowest 100m data were analysed to determine the frequency of ducting per month. Progressive increase in the occurrence of ducting was observed during the rain-harmattan transition phase, which coincides with the West African Monsoon retreat. The results show significant divergence from previous studies, which reported that the tropospheric condition over Lagos (Geo. 6.5°N, 3.3°E), Nigeria, is predominantly super-refractive.

Intraseasonal to interannual variability of Kelvin wave momentum fluxes as derived from high-resolution radiosonde data

Abstract. Observational estimates of Kelvin wave momentum fluxes in the tropical lower stratosphere remain challenging. Here we extend a method based on linear wave theory to estimate daily time series of these momentum fluxes from high-resolution radiosonde data. Daily time series are produced for sounding sites operated by the US Department of Energy (DOE) and from the recent Dynamics of the Madden–Julian Oscillation (DYNAMO) field campaign. Our momentum flux estimates are found to be robust to different data sources and processing and in quantitative agreement with estimates from prior studies. Testing the sensitivity to vertical resolution, our estimated momentum fluxes are found to be most sensitive to vertical resolution greater than 1 km, largely due to overestimation of the vertical wavelength. Climatological analysis is performed over a selected 11-year span of data from DOE Atmospheric Radiation Measurement (ARM) radiosonde sites. Analyses of this 11-year span of data reveal the expected seasonal cycle of momentum flux maxima in boreal winter and minima in boreal summer, and variability associated with the quasi-biennial oscillation of maxima during easterly phase and minima during westerly phase. Comparison between periods with active convection that is either strongly or weakly associated with the Madden–Julian Oscillation (MJO) suggests that the MJO provides a nontrivial increase in the lowermost stratospheric momentum fluxes.

Dependence of atmospheric refractive index structure parameter (Cn2) on the residence time and vertical distribution of aerosols.

Effects of absorbing atmospheric aerosols in modulating the tropospheric refractive index structure parameter (Cn2) are estimated using high resolution radiosonde and multi-satellite data along with a radiative transfer model. We report the influence of variations in residence time and vertical distribution of aerosols in modulating Cn2 and why the aerosol induced atmospheric heating needs to be considered while estimating a free space optical communication link budget. The results show that performance of the link is seriously affected if large concentrations of absorbing aerosols reside for a long time in the atmospheric path.

Derivation of Clear-Air Turbulence Parameters from High-Resolution Radiosonde Data

AbstractThe knowledge of atmospheric refractive index structure constant () profiles is fundamental to determine the intensity of turbulence, and hence the impact of the scintillation impairment on the signals propagating in the troposphere. However, their relation with atmospheric variables is not straightforward, and profiles based on statistical considerations are normally employed. This can be a shortcoming when performing simulations for which scintillation disturbances need to be consistent with the assumed atmospheric conditions. To overcome this limitation, this work describes a procedure to obtain an estimate of the refractive index structure constant profile of clear-air turbulence under given atmospheric conditions. The procedure is based on the application of the vertical gradient approach to high-resolution radiosonde data. Since turbulence is known to be confined to vertically thin layers, a preliminary identification of turbulent layers is required. This is accomplished by analyzing the profiles of the Richardson number. The value of the outer scale length is estimated using the Thorpe length calculated from the potential temperature profile. The procedure is applied to high-resolution radiosonde data that have been acquired from the Stratosphere–Troposphere Processes and their Role in Climate (SPARC) Data Center, and the obtained results are consistent with measured profiles previously published in the literature.

The interaction between the tropopause inversion layer and the inertial gravity wave activities revealed by radiosonde observations at a midlatitude station

AbstractThe interaction between the tropopause inversion layer (TIL) and the inertial gravity wave (IGW) activities is first presented by using a high vertical resolution radiosonde data set at a midlatitude station, Boise, Idaho (43.57°N, 116.22°W), for the period 1998–2008. The tropopause‐based vertical coordinate is used for the TIL detection, and for meticulously studying the IGW variation around the TIL, the broad spectral method is used for the IGW extraction. Generally, the TIL at the midlatitude station is stronger and thicker in winter and spring, which is consistent with previous studies. Our study confirmed the intense interaction between the TIL and IGW. It is found that the TIL not only could inhibit the upward propagation of IGWs from below but also imply the possible excitation links between the TIL and IGW. The results also indicate that the enhanced wind shear layer just 1 km above the tropopause may result in instability and finally leads to the IGW breaking and intensive turbulence. Subsequently, the IGW‐induced intensive turbulence leads to strong wave energy dissipation and a downward heat flux. This downward heat transportation could significantly cool the tropopause, while it has only negligible thermal effect on the atmosphere above the tropopause. Then, the IGW‐induced cooling at the tropopause makes the tropopause colder and sharper and finally forms the TIL. These suggest besides previously proposed mechanisms that IGWs also contribute greatly to the formation of TIL, which is consistent with a recent related simulation study.

Marine Boundary Layer Heights and Their Longitudinal, Diurnal, and Interseasonal Variability in the Southeastern Pacific Using COSMIC, CALIOP, and Radiosonde Data

Abstract The spatial and temporal variability of the marine boundary layer (MBL) over the southeastern Pacific is studied using high-resolution radiosonde data from the VAMOS Ocean–Cloud–Atmosphere–Land Study Regional Experiment (VOCALS-REx), lidar cloud measurements from the CALIOP instrument on the CALIPSO satellite, radio occultation (RO) data from the COSMIC satellites, and the ERA-Interim. The height of the MBL (MBLH) is estimated using three RO-derived parameters: the bending angle, refractivity, and water vapor pressure computed from the refractivity derived from a one-dimensional variational data inversion (1D-VAR) procedure. Two different diagnostic methods (minimum gradient and break point method) are compared. The results show that, although a negative bias in the refractivity exists as a result of superrefraction, the spatial and temporal variations of the MBLH determined from the RO observations are consistent with those from CALIOP and the radiosondes. The authors find that the minimum gradient in the RO bending angle gives the most accurate estimation of the MBL height.

The performance of Aeolus in heterogeneous atmospheric conditions using high-resolution radiosonde data

Abstract. The European Space Agency Aeolus mission aims to measure wind profiles from space. A major challenge is to retrieve high quality winds in heterogeneous atmospheric conditions, i.e. where both the atmospheric dynamics and optical properties vary strongly within the sampling volume. In preparation for launch we aim to quantify the expected error of retrieved winds from atmospheric heterogeneity, particularly in the vertical, and develop algorithms for wind error correction, as part of the level-2B processor (L2Bp). We demonstrate that high-resolution data from radiosondes provide valuable input to establish a database of collocated wind and atmospheric optics at 10 m vertical resolution to simulate atmospheric conditions along Aeolus' lines of sight. The database is used to simulate errors of Aeolus winds retrieved from the Mie and Rayleigh channel signals. The non-uniform distribution of molecules in the measurement bin introduces height assignment errors in Rayleigh channel winds up to 2.5% of the measurement bin size in the stratosphere which translates to 0.5 m s−1 bias for typical atmospheric conditions, if not corrected. The presence of cloud or aerosol layers in the measurement bin yields biases in Mie channel winds which cannot be easily corrected and mostly exceed the mission requirement of 0.4 m s−1. The collocated Rayleigh channel wind solution is generally preferred because of smaller biases, in particular for transparent cloud and aerosol layers with one-way transmission above 0.8. The results show that Aeolus L2Bp, under development, can be improved by the estimation of atmosphere optical properties to correct for height assignment errors and to identify wind solutions potentially detrimental when used in Numerical Weather Prediction.

Estimation of atmospheric mixing layer height from radiosonde data

Abstract. Mixing layer height (h) is an important parameter for understanding the transport process in the troposphere, air pollution, weather and climate change. Many methods have been proposed to determine h by identifying the turning point of the radiosonde profile. However, substantial differences have been observed in the existing methods (e.g. the potential temperature (θ), relative humidity (RH), specific humidity (q) and atmospheric refractivity (N) methods). These differences are associated with the inconsistency of the temperature and humidity profiles in a boundary layer that is not well mixed, the changing measurability of the specific humidity and refractivity with height, the measurement error of humidity instruments within clouds, and the general existence of clouds. This study proposes a method to integrate the information of temperature, humidity and cloud to generate a consistent estimate of h. We apply this method to high vertical resolution (~ 30 m) radiosonde data that were collected at 79 stations over North America during the period from 1998 to 2008. The data are obtained from the Stratospheric Processes and their Role in Climate Data Center (SPARC). The results show good agreement with those from N method as the information of temperature and humidity contained in N; however, cloud effects that are included in our method increased the reliability of our estimated h. From 1988 to 2008, the climatological h over North America was 1675 ± 303 m with a strong east–west gradient: higher values (generally greater than 1800 m) occurred over the Midwest US, and lower values (usually less than 1400 m) occurred over Alaska and the US West Coast.