The crucial parameter for characterizing the energy exchange between the Earth's surface and the atmosphere within the Atmospheric Boundary Layer (ABL) is the latent heat flux (LHF). This represents the speed at which energy stored as latent heat in water vapor molecules is transported into the ABL due to the turbulent convective movement of the air.

The integration of both lidar measurements provides a comprehensive perspective on atmospheric processes related to latent heat flux, significantly contributing to improving the understanding of the water cycle and associated meteorological phenomena. During the WaLiNeAs campaign (Water vapor Lidar Network Assimilation), a consortium of French, German, Italian, and Spanish research groups deployed a network of 6 autonomous Water Vapor (WV) Lidars in the French territory. This network delivers measurements with high vertical resolution and accuracy throughout the Western Mediterranean, starting in the fall of 2022 and addressing critical gaps in water vapor observations in the lower troposphere from current operational networks and satellites.

As part of the WaLiNeAs initiative, a Lidar system developed by the University of Basilicata was positioned near a Wind Lidar with the goal of collecting measurements of heat flux and turbulent kinetic energy (TKE). These two systems operated continuously for three months starting from the end of September 2022, covering the most favorable period in southern France and acquiring high-resolution measurements (10 seconds, 30 meters).

Acknowledgment

The authors acknowledge Next Generation EU Mission 4 “Education and Research” - Component 2: “From research to business” - Investment 3.1: “Fund for the realization of an integrated system of research and innovation infrastructures” - Project IR0000032 – ITINERIS.

This work was supported by the Agence Nationale de la Recherche (WaLiNeAs, Grant ANR-20-CE04-0001). This research was also funded by the Italian Ministry for Education, University and Research (grants STAC-UP and FISR2019-CONCERNING) and the Italian Space Agency (grants As-ATLAS and CALIGOLA).

References

[1] Flamant, C., Chazette, P., Caumont, O. et al. (2021) A network of water vapor Raman lidars for improving heavy precipitation forecasting in  southern      France: introducing the WaLiNeAs initiative. Bull. of Atmos. Sci.& Technol. 2, 10.

[2] Kiemle, W. A. Brewer, G. Ehret, R. M. Hardesty, A. Fix, C. Senff,  M. Wirtg, G. Poberaj and M. A. Lemone. (2007) Latent Heat Flux Profiles from Collocated Airborne Water Vapor and Wind Lidars during IHOP_2002. American Meteorological Society pp:627-639.

[3] Behrendt , V. Wulfmeyer1 , C. Senff , S. K. Muppa, F. Späth , D. Lange , N. Kalthoff , and A. Wieser. (2020). Observation of sensible and latent heat flux profiles with lidar Atmos. Meas. Tech., 13, 3221–3233.

How to cite: Summa, D., D'amico, G., Gandolfi, I., Franco, N., Di Paolantonio, M., Rosoldi, M., De Rosa, B., and Di Girolamo, P.: Latent Heat Flux by Raman Lidar and Wind Lidar system during Walineas Campaign., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3097, https://doi.org/10.5194/egusphere-egu24-3097, 2024.

The Cloud and Aerosol Lidar for Global Scale Observations of the Ocean-Land-Atmosphere System (CALIGOLA) is an advanced multi-purpose space lidar mission with a focus on atmospheric and oceanic observation aimed at characterizing the Ocean-Earth-Atmosphere system and the mutual interactions within it. This mission has been conceived by the Italian Space Agency (ASI) with the aim to provide the international atmospheric and ocean science communities with an unprecedented dataset of geophysical parameters capable to increase scientific knowledge in the areas of atmospheric, aquatic, terrestrial, cryospheric and hydrological sciences. The mission is planned to be launched in the time frame 2030-2031, with an expected lifetime of 3-5.

Exploiting the three Nd:YAG laser emissions at 354.7, 532 and 1064 nm and the elastic (Rayleigh-Mie), depolarized and Raman lidar echoes from atmospheric constituents, CALIGOLA will carry out 3λ profile measurements of the particle backscatter coefficient and depolarization ratio and 1-2λ (354.7 and 532 nm) profile measurements of the particle extinction coefficient from aerosols and clouds. These measurements allow for aerosol typing and the determination of aerosol size and microphysical properties. Furthermore, measurements of the elastic and depolarized backscattered echoes from the sea surface and the underlying layers will allow characterizing the optical properties of the marine surface (ocean color) and the suspended particulate matter in terms of oceanic particulate backscattering coefficient, while diffuse attenuation for downwelling irradiance at 1-2λ will be determined from the H₂O roto-vibrational Raman signals. These measurements will allow characterizing phytoplankton seasonal and inter-annual dynamics. Additionally, fluorescent scattering measurements at 1-3λ (450, 685 and 735 nm) from marine chlorophyll and atmospheric aerosols will be exploited to characterize ocean primary production and for atmospheric aerosol typing, respectively. CALIGOLA will also allow for accurate measurements of the small-scale variability of the earth's surface elevation, primarily associated with variations in the ice and snow, terrain, vegetation and forest canopy height.

The space mission CALIGOLA is explicitly included in the on-going ASI 2021-2023 Activity Plan. A Phase-A study focusing on the technological feasibility of the major sub-systems is on-going, commissioned by ASI to Leonardo S.p.A. (LDO). Scientific studies in support of the mission are also on-going, with the University of Basilicata (UNIBAS) being the leading scientific institution. In September 2023 NASA-LARC initiated a pre-formulation study to assess the feasibility of a possible contribution to CALIGOLA based on the development of the receiver detection chain and data down link capabilities. In September 2024 NASA will decide if proceed or not with the cooperation.

This conference contribution aims at illustrating the different atmospheric and ocean sciences’ objectives and a preliminary assessment of the mission observational requirements in terms of observable quantities, their vertical/horizontal resolution and precision/accuracy. The contribution also aims at illustrating the technical and technological solutions identified in the design of the instrument during the pre-feasibility and feasibility studies carried out by LDO, in cooperation with UNIBAS and other Italian research institutions. Expected system performance in a variety of environmental conditions will be provided based on the application of an end-to-end simulator developed at UNIBAS.

How to cite: Di Girolamo, P., Franco, N., Dionisi, D., Di Paolantonio, M., Summa, D., Lolli, S., Mona, L., Santoleri, R., Zoffoli, S., Tataranni, F., Scopa, T., Longo, F., Sacchieri, V., Perna, A., Cosentino, A., Hu, Y., Behrenfeld, M. J., Hostetler, C. A., Hall, S. R., and Trepte, C. R.: An overview of the Cloud and Aerosol Lidar for Global Scale Observations of the Ocean-Land-Atmosphere System, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4039, https://doi.org/10.5194/egusphere-egu24-4039, 2024.

Water vapor is the key trace gas component of the air and involved in virtually all relevant atmospheric processes. To know the vertical profile with decent resolution is crucial in all cases. For example, there are several regions of the atmosphere where numerical weather prediction models show biases which are not understood. So, after aerosol/cloud and wind lidars have been very successfully applied within space missions, the natural next step would be the profiling of water vapor by a Differential Absorption Lidar (DIAL) from a satellite in a low Earth orbit. About 20 years ago the ESA EarthExplorer Proposal WALES went through phase A, but was not further selected due to the identified technological risks and the corresponding financial efforts. Thanks to the European spaceborne lidar missions Aeolus/2, EarthCare, and MERLIN now the major building blocks for a such water vapor DIAL have reached the necessary technological readiness to realize such a program within the financial limits of a typical Earth observation mission. We will review the benefits of water vapor profiling by lidar as compared to passive sensors for different applications and then present an updated system design based on the current European space lidar component pool. Finally, results from end-to-end performance simulations will be presented. This presentation is thought as an invitation to the community to think about possible applications of space-borne H2O-lidar data and the corresponding observational requirements.

How to cite: Wirth, M., Groß, S., and Fix, A.: Spaceborne Water Vapor DIAL: Has the time come now?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8596, https://doi.org/10.5194/egusphere-egu24-8596, 2024.

The variability of CO₂ in the atmosphere is still not well understood. Key to improve this understanding are continuous measurements of the CO₂ concentration over long periods of time as well as in different altitudes. At the “Land-Atmosphere Feedback Observatory” (LAFO) [1] of the University of Hohenheim, Stuttgart, Germany, we are operating the ground based Raman lidar system ARTHUS. ARTHUS stands for "Atmospheric Raman Temperature and HUmidity Sounder" [2]. This automatic system provides high resolution measurements up to the turbulent scale of temperature, water vapor mixing ratio as well as extinction and backscatter data continuously. But measuring CO₂concentrations with Raman lidar is quite challenging because of its comparatively low concentrationresulting in an overall weak backscatter signal and thus a low signal-to-noise ratio. To investigate the capabilities of our system for capturing CO₂ profiles, we developed and incorporated a new channel. For the measurements we utilize the 2ν₂ CO₂ Raman line, which is well separated from relevant Raman lines of other constituents of the atmosphere (e.g. O₂). At the conference we will present and discuss the first results of the first measurements at the LAFO site between August and October 2023. Comparison of the measured with expected profiles show good agreement. The latter where obtained by appropriately scaling profiles of the water vapor mixing ratio channel of the same system. In the near future, we will add a scanning unit to the system. This will enable us to calibrate and compare the CO₂ lidar data with in-situ instruments located at the ground. Furthermore, the identification and quantification of carbon sources and sinks along the surface will then be possible.

References:

[1] Späth, F., S. Morandage, A. Behrendt, T. Streck, and V. Wulfmeyer, 2021: The Land-Atmosphere Feedback Observatory (LAFO). EGU21-7693 (2021). DOI:10.5194/egusphere-egu21-7693

[2] Lange, D. et al.: Compact Operational Tropospheric Water Vapor and Temperature Raman Lidar with Turbulence Resolution. Geophys. Res. Lett. (2019). DOI:10.1029/2019GL085774

How to cite: Schumacher, M., Lange, D., Behrendt, A., and Wulfmeyer, V.: Measurements of CO2 Profiles in the Lower Troposphere with the new Raman Lidar Channel of ARTHUS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9219, https://doi.org/10.5194/egusphere-egu24-9219, 2024.

We quantitatively assess the aerosol removal of aerosols by precipitation, using lidar, micro rain radar, and disdrometer observations. Precipitation acts as an effective means of cleansing the atmosphere of aerosols through several processes. Fine and coarse aerosol particles are each subject to below-cloud scavenging, characterized by distinct coefficients for each particle category. Data from lidar, micro rain radar, and disdrometers have revealed aerosol depletion at the melting layer, where the wet scavenging coefficient (WSC) is influenced by the rainfall intensity and the interaction efficacy between raindrops and aerosol particles. The synergy of cloud dynamics and precipitation is pivotal in aerosol removal, with lidar data indicating the influence of evaporation and the modulation of latent heat in the process. Precipitation is found to markedly expedite the clearance of aerosols from the air, accounting for up to 80% of the total removal under specific scenarios. This investigation underscores the vital function of precipitation in the dynamics of atmospheric aerosols and sheds light on the consequential environmental and climate-related impacts.

How to cite: Lolli, S., Lewis, J. R., Dolinar, E. K., Campbell, J. R., and Welton, E. J.: Analyzing the Efficacy of Precipitation in Aerosol Clearance Using Lidar, Micro Rain Radar, and Disdrometer Observations., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10293, https://doi.org/10.5194/egusphere-egu24-10293, 2024.

In this contribution, we will give an update of recent lidar activities at University of Hohenheim. Two of the lidars have been developed at our institute: The scanning water vapor differential absorption lidar (WVDIAL) and the Raman lidar ARTHUS (Atmospheric Raman Temperature and HUmidity Sounder). In addition, two scanning Doppler lidars are used since a few years while a third one will be added soon. All these lidars are located at LAFO (Land Atmospheric Feedback Observatory; Branch et al., this conference). Here, also a scanning Doppler cloud radar, meteorological towers, Eddy-covariance stations, surface and sub-surface sensors are collecting routinely data. These data are combined with detailed vegetation analyses.

The WVDIAL is embedded into large truck. Its transmitter consists of an injection-seeded titanium-sapphire laser that is pumped with a diode-pumped Nd:YAG laser. The maximum laser power is 10 W at 200 Hz. This laser power can be used for vertical measurements for which the laser beam is directly emitted vertically into the atmosphere. For scanning measurements, 2 W laser power are transmitted with a fiber into the atmosphere after being expanded with a small telescope. The atmospheric backscatter signals are collected with a 80-cm telescope offering high detection efficiency. The resolution of the stored raw data is up to several Hz and a few meters. The typical resolution of the data products is 1 s and 30 m.

While the large WVDIAL needs supporting personal for its operation, our second lidar ARTHUS is an automated instrument with continuous operation (Lange et al., 2019; Wulfmeyer and Behrendt, 2022). This eyesafe Raman lidar uses a diode-pumped Nd:YAG laser as transmitter. Only the third-harmonic radiation at 355 nm is – after beam expansion – transmitted into the atmosphere. The laser power is about 15 W at 200 Hz repetition rate. The receiving telescope has a diameter of 40 cm. A polychromator extracts the elastic backscatter signal and three inelastic signals, namely the vibrational Raman signal of water vapor, and two pure rotational Raman signals. The raw data is stored with a resolution of 7.5 m and typically 10 s (while higher temporal resolution is possible). All four signals are simultaneously analyzed and stored in both photon-counting (PC) mode and voltage (so-called “analog” mode) in order to make optimum use of the large intensity range of the backscatter signals covering several orders of magnitude. Primary data products are temperature, water vapor mixing ratio, particle backscatter coefficient and particle extinction coefficient. The high resolution allows studies of boundary layer turbulence (Behrendt et al, 2015) and - in combination with the vertical pointing Doppler lidar - sensible and latent heat fluxes (Behrendt et al, 2020). Similar lidars like ARTHUS are meanwhile also available at the company Purple Pulse Lidar Systems (www.purplepulselidar.com). In 2023, a CO₂ channel was implemented into ARTHUS allowing now in addition also measurements of the CO₂ mixing ratio (Schumann et al., this conference).

Behrendt et al. 2015, https://doi.org/10.5194/acp-15-5485-2015

Behrendt et al. 2020, https://doi.org/10.5194/amt-13-3221-2020

Lange et al. 2019, https://doi.org/10.1029/2019GL085774

Wulfmeyer and Behrendt 2022, https://doi.org/10.1007/978-3-030-52171-4_25

How to cite: Behrendt, A., Lange, D., Branch, O., Abbas, S., Schumacher, M., Alnayef, O., and Wulfmeyer, V.: Lidars at University of Hohenheim, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11936, https://doi.org/10.5194/egusphere-egu24-11936, 2024.

The atmospheric boundary layer (ABL) is the lowest part of atmosphere. It is directly influenced by the Earth's surface. To understand the influence of surface fluxes on ABL turbulence processes during daytime in convective conditions, the use of lidars and Eddy covariance stations are essential. Such better understanding will then help to improve weather and climate models. The Land-Atmosphere Feedback Observatory (LAFO) at the University of Hohenheim, Stuttgart, Germany is a designated study site for agricultural experiments equipped with various sensors to analyze state variables from the soil to the lower free troposphere (Späth et al., 2023). To investigate boundary layer turbulence, two Doppler lidars, a Doppler Cloud Radar, the lidar Atmospheric Raman Temperature and Humidity Sounder (ARTHUS) (Lange et al., 2019), and two Eddy covariance stations are deployed at LAFO to capture high-resolution data. Two Doppler lidars are continuously operated, one in vertical pointing mode and the second in six-beam scanning mode (Bonin et al., 2017) to measure high spatial and temporal resolution vertical and horizontal wind data. The turbulent surface fluxes significantly impact the ABL exchange processes. Therefore, it is very interesting to integrate the continuous high temporal resolution measurements of Eddy covariance sensors with lidars measurement. The key turbulent variables are retrieved from high frequency vertical wind data. These turbulence statistics are transversal temporal autocovariance functions, its coefficients in the inertial subrange using appropriate fit lags, atmospheric vertical wind variance, integral time scale, turbulence kinetic energy dissipation (Wulfmeyer et al., 2023), cloud base height and ABL depth. We have used two methods to determine the ABL depth. The first retrieval method is based on fuzzy logic (Bonin et al., 2018) which uses atmospheric vertical velocity variance profiles. The second method employs Haar wavelet transform (Pal et al., 2010) on water vapor mixing ratio and potential temperature profiles.

In this contribution, we are presenting our analyses on correlation statistics between surface fluxes and ABL depth and influence of these surface fluxes on turbulence variables covering different daytime weather conditions from June to August in 2021.

Bonin et al, 2017,  https://doi.org/10.5194/amt-10-3021-2017

Bonin et al, 2018,  https://doi.org/10.1175/JTECH-D-17-0159.1

Lange et al, 2019, https://doi.org/10.5194/egusphere-egu22-3275

Pal et al, 2010, https://doi.org/10.5194/angeo-28-825-2010

Späth et al, 2023, https://doi.org/10.5194/gi-12-25-2023

Wulfmeyer et al, 2023, https://doi.org/10.5194/amt-2023-183

How to cite: Abbas, S. S., Branch, O., Behrendt, A., Lange, D., and Wulfmeyer, V.: Study of the Relationship Between Surface Fluxes and Convective Boundary Layer Dynamics with Lidars. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14294, https://doi.org/10.5194/egusphere-egu24-14294, 2024.

The lack of accurate observations affects the initial conditions of numerical weather prediction (NWP) models resulting in suboptimal forecasts. The assimilation of temperature and moisture profiles obtained from active remote-sensing lidar systems offers great potential for improving the predictive skills of NWP models (Thundathil et al., 2021, Bauer et al. 2023). Advanced data assimilation (DA) techniques, with suitable observational forward operators, enable the model to make use of such observations efficiently.

New lidar systems provide temperature and humidity observations with high accuracy and resolution, which is highly beneficial for DA. The high accuracy avoids the need for a challenging bias correction of the data. It also simplifies operational use and minimizes the latency of the lidar data available for DA.

In this regard, we make use of lidar observations to investigate the extent to which the assimilation of these data through advanced DA systems improves the analyses and corresponding forecasts.

Our automated thermodynamic profiler based on the Raman lidar technique, the Atmospheric Raman Temperature and Humidity Sounder (ARTHUS) (Lange et al. 2019) was deployed in the framework of the WaLiNeAs (Water vapor Lidar Network Assimilation) (Flamant et al. 2021) initiative at the west coast of Corsica between 15 September and 10 December 2022. The participation of ARTHUS was possible due to a project funded by the German Research Foundation (DFG).

Together with ARTHUS, a network of several other autonomous water-vapor lidars was deployed for providing more thermodynamic data across the Western Mediterranean. We expect that this network during its operation closed critical gaps present in lower tropospheric observations of current operational networks and satellite observations.

We will present the first results of the impact of high-resolution temperature and water vapour mixing ratio lidar profiles in our data assimilation studies on heavy precipitation events, using  the WRF 3DVAR-ETKF approach on the kilometer-scale.

How to cite: Lange Vega, D. and the WaLiNeAs (Water vapor Lidar Network Assimilation) Team: Data assimilation of temperature and water-vapor mixing-ratio lidar profiles in WRF, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15570, https://doi.org/10.5194/egusphere-egu24-15570, 2024.

This research focuses on investigating the influence of dynamics and thermodynamics on cloud formation. The properties of the particles in dependence on relative humidity in the atmospheric boundary layer during cloud formation are investigated. For this, we use the synergy of Raman and Doppler lidars as well as of cloud radar operated during the Land-Atmosphere Feedback Experiment (LAFE) (see https://www.arm.gov/research/campaigns/sgp2017lafe). The LAFE project was executed at the Southern Great Plains (SGP) site of the Atmospheric Radiation Measurement (ARM) program in August 2017 in the USA.

The particle backscatter coefficients are measured with Raman lidar, vertical wind velocity with Doppler lidar, and Doppler cloud radar. This instrument combination is also particularly advantageous for investigating the vertical structure of clouds, providing details about cloud height and thickness.

In consequence, the combined measurements allow detailed insights into the relative humidity dependencies on the growth of particles to investigate the influence of dynamics and thermodynamics on cloud formation.

How to cite: Alnayef, O., Behrendt, A., Lange, D., Branch, O., and Wulfmeyer, V.: Investigation of Cloud Formation in the Atmospheric Boundary Layer with a Synergy of Radar and Lidar , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16371, https://doi.org/10.5194/egusphere-egu24-16371, 2024.

Studies of land-atmosphere (L-A) feedbacks are essential for understanding the Earth system. These feedbacks are the result of an interaction of processes related to exchanges of momentum, energy, and mass in the soil-vegetation-surface layer (SL)-atmospheric boundary layer (ABL) continuum. Quantification of feedbacks are often made using L-A feedback metrics. Inaccurate representation/parameterization of feedbacks are a weakness of current weather models, and their improvement will thus contribute to better simulations over all spatiotemporal scales. Improving feedback representation requires simultaneous measurements in all L-A compartments using a synergy of in-situ and active remote sensing instruments. To that end, a new Land-Atmosphere Feedback Observatory (LAFO) was established at the University of Hohenheim, Stuttgart, Germany funded by the Carl Zeiss Foundation. It was developed as a prototype for a future network of GEWEX LAFOs (GLAFOs), proposed by the Global Energy and Water Exchanges (GEWEX) program and GEWEX Global Land/Atmosphere System Study (GLASS) panel (Wulfmeyer et al. 2020). The main goals are to:

1) investigate the diurnal cycle and statistics of ABL temperature, humidity and wind profiles,

2) characterize L-A feedback by suitable metrics.

3) improve parameterizations of vegetation, surface and ABL fluxes,

4) verify mesoscale and turbulence permitting models,

LAFO brings together a sensor synergy with fine spatiotemporal resolution. An extended set of soil physical, plant dynamic as well as meteorological variables throughout the ABL are measured, focusing on evapotranspiration and other exchanges over agricultural landscapes. The LAFO observations with current instruments are continuously archived, according to FAIR data principles (Findable, Accessible, Interoperable, Reusable) and are complemented by additional field campaign measurements.

The first key component of the current LAFO sensor synergy consists of four 3D scanning lidar systems: A scanning water vapor Differential Absorption Lidar (DIAL, Muppa et al. 2016, Späth et al. 2016) and the Atmospheric Rotational-Raman Temperature and Humidity Sounder (ARTHUS, Lange et al. 2019), both developed at the Institute of Physics and Meteorology. Both these systems are unique and provide water vapor and temperature profiles from the surface layer to the free troposphere with fine resolution down to turbulence scales (Behrendt et al. 2015, Wulfmeyer et al. 2015). These lidars are complemented by a scanning Doppler cloud radar and two Doppler lidars for measuring horizontal and vertical wind profiles and turbulent fluctuations. This combination allows determination of sensible and latent heat flux profiles. The second key component is a soil moisture and temperature sensor network distributed over agricultural land and two 10-m towers, measuring turbulent fluxes at two heights.

LAFO will soon form part of a new Research Unit, funded by the German Research Foundation (DFG), called the Land-Atmosphere-Feedback-Initiative (LAFI) which begins in 2024, and incorporates novel crop, hydrology and atmospheric instruments, operated by several research partners within Germany. Here, we present measurement examples from the LAFO and show how these can be used to reach our research goals.

References

Wulfmeyer et al. 2020, GEWEX Quarterly Vol. 30, No. 1.

Behrendt et al. 2015, doi:10.5194/acp-15-5485-2015

Wulfmeyer et al. 2015, doi:10.1002/2014RG000476

Muppa et al. 2016, doi:10.1007/s10546-015-0078-9

Späth et al. 2016, doi:10.5194/amt-9-1701-2016

Lange et al. 2019, doi:10.1029/2019GL085774

How to cite: Branch, O., Behrendt, A., Lange, D., Abbas, S., Schumacher, M., Streck, T., and Wulfmeyer, V.: A New Land-Atmosphere Feedback Observatory (LAFO), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18096, https://doi.org/10.5194/egusphere-egu24-18096, 2024.

The Raman lidar technique to measure atmospheric temperature profiles is based on the dependence on temperature of the intensity of the atmospheric N₂ and O₂ rotational Raman lines [1]. The technique requires very good stability of the laser wavelength, or frequent recalibrations, to avoid errors in the retrieved temperature produced by wavelength drifts.  Frequency doubled or tripled Nd:YAG lasers are usually employed to implement this technique. To achieve laser wavelength stability, injection-seeded lasers are used that transfer the wavelength stability of the seeder to the high-power laser [2]; this has also the consequence of narrowing the spectrum of the transmitted radiation. Temperature profiling using free-running lasers are also reported in the literature [3]. In this case wavelength stability must be obtained by keeping the laser operating conditions, and in particular the Nd:YAG rod temperature, very stable.

We have assessed the effects on the atmospheric temperature retrieval of the spectral width and temperature-induced wavelength drift of the 3^rd harmonic of a free-running Nd:YAG laser. We have found that the spectral width has a negligible effect, as compared with the negligible spectral width of an injection-seeded laser, in the receiving filters that are part of the lidar. However, slight temperature-induced drifts on the central wavelength of the laser emitted spectrum entail small changes in the filter responses that impair the calibration and cause an uncertainty in the retrieved atmosphere temperature. We have estimated that to keep the retrieved temperature uncertainty below 1 K, the rod temperature must also to be kept within a ±1 K range. This is also the temperature stability that would be needed in the seeder of an injection seeded laser, as changes of temperature in the seeder will also cause wavelength drifts, hence uncontrolled biases in the atmosphere temperature measurements that would add to their uncertainty.   

[1] J. Cooney, Measurement of Atmospheric Temperature Profiles by Raman Backscatter, J Appl Meteorol Climatol. 11 (1972) 108–112. https://doi.org/10.1175/1520-0450(1972)011<0108:MOATPB>2.0.CO;2

[2] E. Hammann, A. Behrendt, F. Le Mounier, V. Wulfmeyer, Temperature profiling of the atmospheric boundary layer with rotational Raman lidar during the HD(CP)2 Observational Prototype Experiment, Atmos Chem Phys. 15 (2015) 2867–2881. https://doi.org/10.5194/acp-15-2867-2015.

[3] P. Di Girolamo, R. Marchese, D.N. Whiteman, B.B. Demoz, Rotational Raman Lidar measurements of atmospheric temperature in the UV, Geophys Res Lett. 31 (2004) 1–5. https://doi.org/10.1029/2003GL018342.

How to cite: Comerón, A., Zenteno-Hernández, J. A., Dios, F., Rodríguez-Gómez, A., Muñoz-Porcar, C., Sicard, M., Franco, N., Behrendt, A., and Di Girolamo, P.: Temperature stability requirements of free-running Nd:YAG lasers for atmospheric temperature profiling through the rotational Raman technique, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20443, https://doi.org/10.5194/egusphere-egu24-20443, 2024.