ALBERT

Description: We investigate the influence of the sea surface temperature (SST) changes on the middle atmosphere of a tidally locked Earth-like planet orbiting a G star using the coupled 3D chemistry-climate model CESM1(WAC...

Description: Ground- and space-based Global Navigation Satellite System (GNSS) receivers can provide three-dimensional (3D) information about the occurrence of equatorial plasma bubbles (EPBs). For this study, we selected March 2014 data (during solar maximum of cycle 24) for the analysis. The timing and the latitudinal dependence of the EPBs occurrence rate are derived by means of the rate of the total electron content (TEC) index (ROTI) data from GNSS receivers in China, whereas vertical profiles of the scintillation index S4 are provided by COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate). The GNSS receivers of the low Earth orbit satellites give information about the occurrence of amplitude scintillations in limb sounding geometry where the focus is on magnetic latitudes from 20° S to 20° N. The occurrence rates of the observed EPB-induced scintillations are generally smaller than those of the EPB-induced ROTI variations. The timing and the latitude dependence of the EPBs occurrence rate agree between the ground-based and spaceborne GNSS data. We find that EPBs occur at 19:00 LT and they are mainly situated above the F2 peak layer which descended from 450 km at 20:00 LT to 300 km at 24:00 LT in the equatorial ionosphere. At the same time, the spaceborne GNSS data also show, for the first time, a high occurrence rate of post-sunset scintillations at 100 km altitude, indicating the coexistence of equatorial sporadic E with EPBs.

Description: Cloud fraction (CF) is known as the dominant modulator of Earth’s radiative fluxes. Ground-based CF observations are useful to characterize the cloudiness of a specific site and are valuable for comparison with satellite observations and numerical models. We present for the first time CF statistics (relative to liquid clouds only) for Bern, Switzerland, derived from the observations of a ground-based microwave radiometer. CF is derived with a new method involving the analysis of the integrated liquid water distribution measured by the radiometer. The 10-year analyzed period (2004–2013) allowed us to compute a CF climatology for Bern, showing a maximum CF of 60.9% in winter and a minimum CF of 42.0% in summer. The CF monthly anomalies are identified with respect to the climatological mean values, and they are confirmed through MeteoSwiss yearly climatological bulletins. The CF monthly mean variations are similar to the observations taken at another Swiss location, Payerne, suggesting a large-scale correlation between different sites on the Swiss Plateau. A CF diurnal cycle is also computed, and large intraseasonal variations are found. The overall mean CF diurnal cycle, however, shows a typical sinusoidal cycle, with higher values in the morning and lower values in the afternoon.

Description: The Whole Atmosphere Community Climate Model was used to investigate the influences of solar fluctuations on zonal wind oscillations. Two simulations were conducted with short-term solar forcing (

Description: We simulate the 3D ozone distribution of a tidally locked Earth-like exoplanet using the high-resolution, 3D chemistry-climate model CESM1(WACCM) and study how the ozone layer of a tidally locked Earth (TLE) (

Description: The climate model CESM-WACCM is used to study the way a soil colour change of the eastern region of the Sahara affects the dynamics of the troposphere. The soil colour is darkened for 5 days. The difference between the perturbed model run and the control model run is used to isolate the soil colour change-induced atmospheric perturbation from random atmospheric waves which are stronger by an order of magnitude or more. The perturbation generates a circular wave radially propagating away from the Sahara on the first day of the simulation. After nine hours, the wave front reaches the convection zone in Brazil where a secondary wave is generated and can be clearly seen until 23:00 UT. The mean wave velocities of the traveling atmospheric disturbances are 〈v〉=200±50 m/s for the primary wave and 〈v〉=220±40 m/s for the secondary wave. The mean horizontal wavelengths are 〈λ〉=3000±500 km for the primary wave and 〈λ〉=2600±600 km for the secondary wave. The mean wave periods are 〈p〉=4±1 h for the primary wave and 〈p〉=3±1 h for the secondary wave. Since the perturbed model run diverges from the control run with the passage of time, the attribution of cause and effect becomes difficult after a few days. Analysis of the simulation data of the first day leads to a deeper understanding of global teleconnections, radiative transfer and wave-coupling processes between the surface and the atmospheric layers.

Description: It is often stated that short-term precipitation of synoptical weather is related to trends or interannual variations of precipitation. We analyzed nine long-term series of daily precipitation values of the Global Historical Climatology Network (GHCN-D V2.0). Generally, the mean amplitude of short-term variations increases (decreases) if there is a positive (negative) interannual anomaly of precipitation, respectively. In all cases, the amplitude of the short-term variations (periods 〈 10 days) clearly correlates with the long-term variations (periods 〉 1.5 years) of precipitation. The correlation coefficient is between 0.7 and 0.95 at periods 〈8 days. For Kukuihaele (Hawaii), the correlation maximizes at a period of about 14 days. In the other cases, the maximum of the correlation is reached at periods 〈5 days.

Description: Atmosphere, Vol. 9, Pages 171: Mesospheric Inversion Layers at Mid-Latitudes and Coincident Changes of Ozone, Water Vapour and Horizontal Wind in the Middle Atmosphere Atmosphere doi: 10.3390/atmos9050171 Authors: Klemens Hocke Martin Lainer Leonie Bernet Niklaus Kämpfer We analyse middle atmospheric profiles of temperature, geopotential height, water vapour volume mixing ratio, and ozone volume mixing ratio above Bern (46.95 ∘ N, 7.44 ∘ E). These profiles were observed by the satellite experiment Aura/MLS and the ground-based microwave radiometers MIAWARA and GROMOS at Bern. The data series of Aura/MLS and GROMOS extend from the winter 2004/2005 to the winter 2017/2018 while the MIAWARA series starts in winter 2007/2008. Mesospheric inversion layers (MILs) above Bern, Switzerland are often present during the winter season, and the temperature peak of the MIL is located at an altitude of about 81 km in winter. The occurrence rate of the MIL during the winter season above Bern is about 42%. The MILs are possibly associated with planetary wave breaking processes in the mesospheric surf zone at mid-latitudes during winter. The study only evaluates daily averages in order to reduce tidal influences. Composite atmospheric profiles are computed for times when the MIL is present and for times when the MIL is absent. The difference of the composites indicates that middle and upper stratospheric ozone are reduced by up to 7% when the MIL is present while lower mesospheric water vapour is enhanced by up to 20% during the MIL occurrence. Using wind data of ECMWF operational analysis, we find that eastward and northward winds are decelerated by about 5–15 m/s in the lower mesosphere during the occurrence of an MIL. We also find that the occurrence of an MIL above Bern is not a regional process, but it depends on the movements and deformations of the polar mesospheric vortex. During an MIL, the location of Bern is outside of the lower mesospheric vortex. These new findings of atmospheric composition and circulation changes support the assumption that winter MILs at mid-latitudes are connected to planetary wave breaking in the middle atmosphere.

Description: Remote Sensing, Vol. 9, Pages 909: Diurnal Cycle in Atmospheric Water over Switzerland Remote Sensing doi: 10.3390/rs9090909 Authors: Klemens Hocke Francisco Navas-Guzmán Lorena Moreira Leonie Bernet Christian Mätzler The TROpospheric WAter RAdiometer (TROWARA) is a ground-based microwave radiometer with an additional infrared channel observing atmospheric water parameters in Bern, Switzerland. TROWARA measures with nearly all-weather capability during day- and nighttime with a high temporal resolution (about 10 s). Using the almost complete data set from 2004 to 2016, we derive and discuss the diurnal cycles in cloud fraction (CF), integrated liquid water (ILW) and integrated water vapour (IWV) for different seasons and the annual mean. The amplitude of the mean diurnal cycle in IWV is 0.41 kg/m 2 . The sub-daily minimum of IWV is at 10:00 LT while the maximum of IWV occurs at 19:00 LT. The relative amplitudes of the diurnal cycle in ILW are up to 25% in October, November and January, which is possibly related to a breaking up of the cloud layer at 10:00 LT. The minimum of ILW occurs at 12:00 LT, which is due to cloud solar absorption. In case of cloud fraction of liquid water clouds, maximal values of +10% are reached at 07:00 LT and then a decrease starts towards the minimum of −10%, which is reached at 16:00 LT in autumn. This breakup of cloud layers in the late morning and early afternoon hours seems to be typical for the weather in Bern in autumn. Finally, the diurnal cycle in rain fraction is analysed, which shows an increase of a few percent in the late afternoon hours during summer.

Description: Thermospheric gravity waves (GW) in the bottomside F region have been proposed to play a key role in the generation of equatorial plasma bubbles (EPB). However, direct observations of such waves are scarce. This study provides a systematic survey of medium-scale (〈620 km) neutral atmosphere perturbations at this critical altitude in the tropics, using four years of in-situ GOCE satellite measurements of thermospheric density and zonal wind. The analysis reveals pronounced features on their global distribution and seasonal variability: 1. A prominent 3-peak longitudinal structure exists in all seasons, with stronger perturbations over continents than over oceans. 2. Their seasonal variation consists of a primary semiannual oscillations (SAO) and a secondary annual oscillation (AO). The SAO component maximizes around solstices and minimizes around equinoxes, while the AO component maximizes around June solstice. These GW features resemble those of EPBs in spatial distribution but show opposite trend in climatological variations. This may imply that stronger medium-scale GW activity does not always lead to more EPBs. Possible origins of the bottomside GWs are discussed, among which tropical deep convection appears to be most plausible.