Operative forecasting of the fog is still a challenge. The numerical weather prediction (NWP) models frequently miss the spatial and temporal location or onset and the dissipation the fog. Even the recently developed microphysics schemes (e.g. Thompson Aerosol Aware scheme (hereafter TAAS)), evaluate the rate of the activation of the hygroscopic aerosol particles as a function of the vertical velocity. However, in the case of fog, the updraft is usually negligible, therefore this method is physically inconsistent.

A novel parameterization technique was developed to evaluate the rate of aerosol activation in fog. This novel scheme was implemented into WRF, TAAS microphysical module. The novel parametrization calculates the activation rate as a function of local cooling rate, and as a function of local change of water vapor content. Furthermore, a diagnostic variable was introduced to evaluate the visibility reduction due to the formation of haze droplets.

A well observed radiative fog event was used, to demonstrate the capabilities of the novel parametrization. Data from standard meteorological stations, and a measurement campaign at Budapest are available to test the numerical model.

The results are as follows: (i) While the original TAAS activates the aerosols homogeneously throughout the fog (the prescribed minimum value for the updraft velocity is constant in both space and time), the novel parameterization scheme results in significant spatial and temporal variability of the droplets concentration. The impact of the cooling is well demonstrated by the enhanced activation rate at the top of the fog. (ii) In the dissipation period the spatial extension of the fog simulated by novel parameterization fit better to the satellite data than that of calculated by the updraft based parameterization. The novel activation scheme increases the life time of the fog by 30 – 60 min. (iii) Gradual decrease and increase of the visibility can be simulated by calculating of the visibility reduction due to the haze (iv) Comparison of the observed and simulated data shows that the early dissipation of the simulated fog not necessarily the consequence of the overestimation of downward short wave flux.

The results of further case studies for different types of fog are planned to present.

How to cite: Peterka, A. and Geresdi, I.: Improvement of numerical simulation of fog: Implementation of a novel scheme in WRF Thompson Aerosol Aware module to simulate the activation of aerosol particles, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-61, https://doi.org/10.5194/ems2023-61, 2023.

Antarctic Peninsula (AP) glaciers experiencing mean summer air temperature near the melting point are highly sensitive to both long‑term climate variability and short-term but intense warm air advection events. Large scale flow during these events could be further modified by interaction with topography, e.g., by foehn development at the eastern coast of 1000 – 2000 m high AP mountain range. Foehn effect on glacier melt was extensively studied at the Larsen C Ice Shelf region. However, less attention was given to ablation events occurring at the northeastern coast, where AP mountains are less prominent, and where flow interacts also with complex topography of western Weddell Sea islands. In this contribution, we present an analysis of three pronounced melt events in summer 2022/2023 observed on the Davies Dome glacier (514 m a.s.l.) and a cirque-based Triangular Glacier (180 m a.s.l.), both located on Ulu Peninsula, northern James Ross Island. Melt events were identified and their intensity was quantified with an ultrasonic depth sensor data supplemented by snow and ice density observations. The selected events induced total snow/ice melt of ~1.19 m water equivalent (Triangular Glacier) and ~0.28 m water equivalent (Davies Dome) and significantly contributed to an anomalous ablation season 2022/2023 in this region. In-situ air temperature, wind speed, albedo, and net radiation observations allowed identification of crucial meteorological factors leading to snow and ice melt. Differences in melt regime of studied glaciers were further discussed. In addition to in-situ measurements, the Weather Research and Forecasting (WRF) model was run in a very high resolution for investigated events. The model output allowed analysis of synoptic-scale advection patterns leading to enhanced glacier ablation. An attention was given also to the effects of AP mountains and James Ross Island topography on incoming flow characteristics and possible foehn development.

How to cite: Matějka, M., Láska, K., and Zdeněk, S.: Meteorological forcing of unusually high glacier melt on James Ross Island, Antarctic Peninsula in summer 2022/2023:  in-situ observations and WRF model simulations, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-223, https://doi.org/10.5194/ems2023-223, 2023.

The summer of 2022 in the Basque Country was characterized by extremely dry and hot conditions. In a major part of the region, precipitation levels were 50% below average, and the mean temperature was 2.4 ºC higher than the 1981-2010 climatology. This made it the warmest summer on record, second only to 2003. In the midst of this arid and sweltering season, a historic persistent and high temperatures event occurred between July 13th and 18th. During the episode, maximum temperatures exceeded 40 ºC in some areas for several consecutive days, with the highest recorded temperature reaching 43.6 ºC. Minimum temperatures were also persistently high, with some stations not dropping below 20 or even 25 ºC during the warmest days.

Given the extreme and challenging context in terms of surface heating and evapotranspiration, we assessed the ability of the WRF model with a operational forecasting configuration to reproduce the observed atmospheric conditions during the estudied case. Although wind patterns and hourly temperature evolution where generally well-reproduced, maximum temperatures were slightly underestimated and minimum temperatures were greatly overestimated in some areas. Specifically, the WRF configuration did not accurately capture the local weakening of wind at night and the subsequent formation of surface-based thermal inversions on days when offshore southerly winds prevailed.

In this work we present different aspects related with the fine-tune temperature prediction during this significant heatwave episode. We present results from different sensitivity experiments on the operational configuration. We tested various dynamics options, finer land-use databases, and physical parameterizations. We also include some comparison results with other forecast systems available in Euskalmet as other mesoescale models or statistical prediction systems.

How to cite: Arrillaga, J. A., R. Gelpi, I., Diaz de Arcaya, A., Castaño, A., and Gaztelumendi, S.: Evaluating the WRF model’s ability to predict extreme temperatures :  a record-breaking high temperatures case in the Basque Country, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-255, https://doi.org/10.5194/ems2023-255, 2023.