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The effect of modified equator‐to‐pole temperature gradients on the jet stream by low‐level polar warming and upper‐level tropical warming is not fully understood. We perform aquaplanet simulations to quantify the impact of different sea surface temperature distributions on jet stream strength, large wave amplitudes and extreme waviness. The responses to warming in the waviness metrics Sinuosity Index and Local Wave Activity are sensitive to the latitude range over which they are calculated. Therefore, we use a latitude range that accurately represents the position of the jet. The uniform warming scenario strengthens the jet and reduces large wave amplitudes. Reductions in meridional temperature gradients lead to weakened mid‐latitudinal jet strength and show significant decreases in large wave amplitudes and jet stream waviness. These findings contradict the mechanism that weakened jet streams increase wave amplitudes and extreme jet stream waviness. We conclude that weakened jet streams do not necessarily become wavier. Plain Language Summary: This research letter considers how different patterns of atmospheric warming, like low‐level warming at the poles and at high altitude in the tropics, impact the jet stream, which is a strong "river" of high‐altitude wind. We use numerical model simulations to mimic different scenarios of warming that maintain or reduce the temperature gradient between equator and poles. We find that when an Earth‐like planet completely covered by water warms in specific ways, it strengthens the jet stream when it is warmed uniformly or weakens the jet stream when only mid‐ and high latitudes are warmed. For the simulations with a reduced mid‐latitudinal temperature gradient, the size of largest jet stream waves reduces and makes the extreme waviness episodes less wavy. This research letter conclude that weakened jet streams do not necessarily become wavier, which opposes the popular paradigm that weakened jet streams become wavier due to warming in polar regions. Key Points: On an aquaplanet, weakened jet streams do not become wavier with reduced temperature gradients due to warming in mid‐ and high latitudesIn reduced temperature gradient simulations, the magnitude of large wave amplitudes and jet stream extreme waviness decrease robustlyThe Sinuosity Index and the Local Wave Activity waviness metrics are sensitive to the latitude range over which they are calculated [ABSTRACT FROM AUTHOR]

An explanatory model study is presented on semivolatile secondary inorganic aerosols on three clear days in May 2008 during the IMPACT campaign at the Cabauw tower in the Netherlands. A single column model in combination with the equilibrium aerosol model ISORROPIA is used. This model uses surface observations from IMPACT and calculates the gas-aerosol partitioning of ammonium nitrate. The calculated gas-aerosol equilibrium overestimates the gas phase fraction during daytime, and overestimates the aerosol phase fraction during night-time. This discrepancy can partly be solved when the approach of the gas-aerosol equilibrium is forced to proceed with a delay timescale of up to two hours. Although it is shown that the delay itself has a small effect, the most important effect is caused by the mixing of air from higher altitudes at which the equilibrium is shifted to the aerosol phase. Thus, vertical mixing is shown to have a significant influence on the calculated partitioning at the surface. On some occasions, the correspondence to the observed partitioning improves dramatically. Even though gas-aerosol partitioning of ammonium nitrate is not instantaneous, observations show that a different equilibrium in the upper boundary layer causes aerosol ammonium nitrate concentrations to increase with altitude. Our model calculates similar vertical gradients depending on the assumed speed of gas-aerosol equilibrium. The calculated optical properties of the aerosol show a similar behaviour. The aerosol optical properties depend on the aerosol size distribution both directly, because light scattering depends on particle size, and indirectly, because the equilibration timescale depends on the aerosol sizes. Future studies should therefore focus on a fully size-resolved treatment of the gas-aerosol partitioning. Finally, coarser-resolution models may treat the gasaerosol equilibrium of ammonium nitrate by calculating the equilibrium with a temperature and humidity sampled at a different altitude. We found that the equilibrium at an altitude of 200m (night) up to 600m (day) is representative for the partitioning of ammonium nitrate at the surface in the beginning of May 2008. [ABSTRACT FROM AUTHOR]

Interpretation of observed diurnal carbon dioxide (CO2) mixing ratios near the surface requires knowledge of the local dynamics of the planetary boundary layer. In this paper, we quantify the relationship between the boundary layer dynamics and the CO2 budget in convective conditions through a newly derived set of analytical equations. From these equations, we are able to quantify how uncertainties in boundary layer dynamical variables or in the morning CO2 distribution in the mixed-layer or in the free atmosphere influence the bulk CO2 mixing ratio. We find that the largest uncertainty incurred on the mid-day CO2 mixing ratio comes from the prescribed early morning CO2 mixing ratios in the stable boundary layer, and in the free atmosphere. Errors in these values influence CO2 mixing ratios inversely proportional to the boundary layer depth (h), just like uncertainties in the assumed initial boundary layer depth and surface CO2 flux. The influence of uncertainties in the boundary layer depth itself are one order of magnitude smaller. If we "invert" the problem and calculate CO2 surface exchange from observed or simulated CO2 mixing ratios, the sensitivities to errors in boundary layer dynamics also invert: they become linearly proportional to the boundary layer depth. We demonstrate these relations for a typical well characterized situation at the Cabauw tower in the Netherlands, and conclude that knowledge of the temperature and carbon dioxide vertical profiles in the early morning are of vital importance to correctly interpret observed CO2 mixing ratios during midday. [ABSTRACT FROM AUTHOR]

The article discusses the extensive description of the physical and numerical formulation of the Dutch Atmospheric Large-Eddy Simulation (DALES). The model can be applied to studies including atmospheric boundary layer, flow over sloping or heterogeneous terrain, and dispersion of inert and chemically active species. The resolution of turbulent scales larger than a certain filter width and the parameterization of smaller, less energetic scales are aimed in Large-Eddy Simulations (LES).