ASAM v2.7: a compressible atmospheric model with a Cartesian cut cell approach

Jähn, Michael; Knoth, Oswald; König, Marcel; Vogelsberg, Ulrike

doi:10.5194/gmd-8-317-2015

Cited by 17 publications

(22 citation statements)

References 54 publications

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“…This study showed that a flat island with the characteristics of the Santiago Island (Cabo Verde) can induce the generation of gravity waves and enhance the aerosol downward mixing, only through its heat island effect, without taking into account its orography. Another recent LES study (Jähn et al, 2016) conducted in the Barbados area also revealed the presence of island induced gravity waves on the lee side of the island and provided further insight into the dust turbulent downward mixing, cloud generation and boundary layer modification in the lee side of the island. In contrast with the previous case, the heating effect and the orography were taken into account in this case.…”

Section: F Chouza Et Al: Vertical Wind Retrieved By Airborne Lidar mentioning

confidence: 78%

Vertical wind retrieved by airborne lidar and analysis of island induced gravity waves in combination with numerical models and in situ particle measurements

et al. 2016

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Abstract. This study presents the analysis of island induced gravity waves observed by an airborne Doppler wind lidar (DWL) during SALTRACE. First, the instrumental corrections required for the retrieval of high spatial resolution vertical wind measurements from an airborne DWL are presented and the measurement accuracy estimated by means of two different methods. The estimated systematic error is below −0.05 m s−1 for the selected case of study, while the random error lies between 0.1 and 0.16 m s−1 depending on the estimation method. Then, the presented method is applied to two measurement flights during which the presence of island induced gravity waves was detected. The first case corresponds to a research flight conducted on 17 June 2013 in the Cabo Verde islands region, while the second case corresponds to a measurement flight on 26 June 2013 in the Barbados region. The presence of trapped lee waves predicted by the calculated Scorer parameter profiles was confirmed by the lidar and in situ observations. The DWL measurements are used in combination with in situ wind and particle number density measurements, large-eddy simulations (LES), and wavelet analysis to determine the main characteristics of the observed island induced trapped waves.

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Section: F Chouza Et Al: Vertical Wind Retrieved By Airborne Lidar mentioning

confidence: 78%

Vertical wind retrieved by airborne lidar and analysis of island induced gravity waves in combination with numerical models and in situ particle measurements

et al. 2016

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“…The soil class "loam" was chosen to represent the average island soil type. Hydraulic and thermal parameters of this soil type can be found in Doms et al (2011) and Jähn et al (2015). For land surface parameterization, "shrubland" appears to be a good compromise between coastal beach areas and forest in the island interior.…”

Section: Forcingsmentioning

confidence: 99%

“…An extensive model description is presented in Jähn et al (2015), both covering numerical discretization methods and physical parameterizations. A special feature of ASAM is the usage of so-called cut cells for the orography.…”

Section: Model Setupmentioning

confidence: 99%

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Investigations of boundary layer structure, cloud characteristics and vertical mixing of aerosols at Barbados with large eddy simulations

et al. 2016

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Abstract. Large eddy simulations (LESs) are performed for the area of the Caribbean island Barbados to investigate island effects on boundary layer modification, cloud generation and vertical mixing of aerosols. Due to the presence of a topographically structured island surface in the domain center, the model setup has to be designed with open lateral boundaries. In order to generate inflow turbulence consistent with the upstream marine boundary layer forcing, we use the cell perturbation method based on finite amplitude potential temperature perturbations. In this work, this method is for the first time tested and validated for moist boundary layer simulations with open lateral boundary conditions. Observational data obtained from the SALTRACE field campaign is used for both model initialization and a comparison with Doppler wind and Raman lidar data. Several numerical sensitivity tests are carried out to demonstrate the problems related to "gray zone modeling" when using coarser spatial grid spacings beyond the inertial subrange of three-dimensional turbulence or when the turbulent marine boundary layer flow is replaced by laminar winds. Especially cloud properties in the downwind area west of Barbados are markedly affected in these kinds of simulations. Results of an additional simulation with a strong trade-wind inversion reveal its effect on cloud layer depth and location. Saharan dust layers that reach Barbados via long-range transport over the North Atlantic are included as passive tracers in the model. Effects of layer thinning, subsidence and turbulent downward transport near the layer bottom at z ≈ 1800 m become apparent. The exact position of these layers and strength of downward mixing is found to be mainly controlled atmospheric stability (especially inversion strength) and wind shear. Comparisons of LES model output with wind lidar data show similarities in the downwind vertical wind structure. Additionally, the model results accurately reproduce the development of the daytime convective boundary layer measured by the Raman lidar.

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“…Simulations associated with the MelCol 2015 measurement campaign are performed with the All Scale Atmospheric Model (ASAM, Jähn et al, 2015). It has recently been used to investigate heat island effects on atmospheric boundary layer modification, cloud initiation and vertical tracer mixing in the trade wind regime (Jähn et al, 2016).…”

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confidence: 99%

Airborne observations of newly formed boundary layer aerosol particles under cloudy conditions

Altstädter¹,

Platis²,

Jähn³

et al. 2018

Preprint

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Abstract. This study describes the formation of freshly formed boundary layer aerosol particles under classical called "non favourable" conditions by the existence of low-level strato cumulus clouds. Airborne measurements for vertical profiling atmospheric boundary layer properties and aerosol particles in the diameter range between 5 nm and 10 µm were repeatedly performed with the unmanned aerial system ALADINA (Application of Light-weight Aircraft for Detecting IN-situ Aerosol) at the research site of TROPOS (Leibniz Institute for Tropospheric Research) in Melpitz during three seasons between October 5 2013 and July 2015. More than 100 measurement flights were performed during this period on 23 different days with a total flight duration of 53 h. On 26 % of the measurement days, new particle formation was measured close to the inversion layer and was observed to be transported downwards during short time intervals of cloud gaps. However, the typical banana shape of new particle formation and growth was not seen at ground, only sporadic events appeared with low particle growth rate and thus might not have been classified as NPF by pure surface studies. This presentation focuses on two cases influenced by the 10 passage of a low pressure system and minimal concentrations of SO 2 as indicator for precursor gases at ground; I) on April 4, 2014 by east wind and II) on June 21, 2015 under south-west wind. For a closure, an LES-model output was used for the second study in order to derive a full analysis of atmospheric boundary layer growth over the measurement site at small-scale with high spatial resolution. Pronounced turbulent fluxes of sensible and latent heat in the vertical distribution initiated fast mixing processes of freshly formed boundary layer aerosol. Furthermore, CO 2 and particle fluxes indicated downward transport and 15 high deposition during sporadic nucleation events, so that NPF occurrence above with subsequent downward transport was clearly identified.

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ASAM v2.7: a compressible atmospheric model with a Cartesian cut cell approach

Cited by 17 publications

References 54 publications

Vertical wind retrieved by airborne lidar and analysis of island induced gravity waves in combination with numerical models and in situ particle measurements

Vertical wind retrieved by airborne lidar and analysis of island induced gravity waves in combination with numerical models and in situ particle measurements

Investigations of boundary layer structure, cloud characteristics and vertical mixing of aerosols at Barbados with large eddy simulations

Airborne observations of newly formed boundary layer aerosol particles under cloudy conditions

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