Abstract. The effect of aerosol on clouds poses one of the largest uncertainties in estimating the anthropogenic contribution to climate change. Small human-induced perturbations to cloud characteristics via aerosol pathways can create a change in the top-of-atmosphere radiative forcing of hundreds of Wm −2 . Here we focus on links between aerosol and deep convective clouds of the Atlantic and Pacific Intertropical Convergence Zones, noting that the aerosol environment in each region is entirely different. The tops of these vertically developed clouds consisting of mostly ice can reach high levels of the atmosphere, overshooting the lower stratosphere and reaching altitudes greater than 16 km. We show a link between aerosol, clouds and the free atmosphere wind profile that can change the magnitude and sign of the overall climate radiative forcing.We find that increased aerosol loading is associated with taller cloud towers and anvils. The taller clouds reach levels of enhanced wind speeds that act to spread and thin the anvil clouds, increasing areal coverage and decreasing cloud optical depth. The radiative effect of this transition is to create a positive radiative forcing (warming) at top-of-atmosphere.Furthermore we introduce the cloud optical depth (τ ), cloud height (Z) forcing space and show that underestimation of radiative forcing is likely to occur in cases of non homogenous clouds. Specifically, the mean radiative forcing of towers and anvils in the same scene can be several times greater than simply calculating the forcing from the mean cloud optical depth in the scene.Correspondence to: I. Koren (ilan.koren@weizmann.ac.il) Limitations of the method are discussed, alternative sources of aerosol loading are tested and meteorological variance is restricted, but the trend of taller clouds, increased and thinner anvils associated with increased aerosol loading remains robust through all the different tests and perturbations.

Abstract. The effect of aerosol on clouds poses one of the largest uncertainties in estimating the anthropogenic contribution to climate change. In contrast, even small human-induced perturbations in cloud coverage, lifetime, height or optical properties can change the instantaneous radiative energy flux by hundreds of watts per unit area, and this forcing can be either warming or cooling. Clouds and aerosols form a complex coupled system that, unlike greenhouse gases, have relatively short lifetime (hours to days) and inhomogeneous distribution. This and the inherent complexity of cloud microphysics and dynamics, and the strong coupling with meteorology explain why the estimation of the overall effect of aerosol on climate is so challenging. Here we focus on the effect of aerosol on cloud top properties of deep convective clouds over the tropical Atlantic. The tops of these vertically developed clouds consist of mostly ice and can reach high levels of the atmosphere, overshooting the lower stratosphere and reaching altitudes greater than 16 km. We show a link between aerosol, clouds and the free atmosphere wind profile that can change the magnitude and sign of the overall climate radiative forcing. This study demonstrates the deep link between cloud shape and aerosol loading and that the overall aerosol effect in regions of deep convective clouds might be warming. Moreover we show how averaging the cloud height and optical properties over large regions may lead to a false cooling estimation.

The molecular chaperone GroEL exists in at least two allosteric states, T and R, that interconvert in an ATP-controlled manner. Thermodynamic analysis suggests that the T-state population becomes negligible with increasing ATP concentrations, in conflict with the requirement for conformational cycling, which is essential for the operation of molecular machines. To solve this conundrum, we performed fluorescence correlation spectroscopy on the single-ring version of GroEL, using a fluorescent switch recently built into its structure, which turns "on," i.e., increases its fluorescence dramatically, when ATP is added. A series of correlation functions was measured as a function of ATP concentration and analyzed using singular-value decomposition. The analysis assigned the signal to two states whose dynamics clearly differ. Surprisingly, even at ATP saturation, ∼50% of the molecules still populate the T state at any instance of time, indicating constant out-of-equilibrium cycling between T and R. Only upon addition of the cochaperonin GroES does the T-state population vanish. Our results suggest a model in which the T/R ratio is controlled by the rate of ADP release after hydrolysis, which can be determined accordingly.allostery | conformational dynamics | fluorescence correlation spectroscopy | molecular chaperones | chaperonins A TP-driven protein machines are abundant and contribute to multiple essential biological processes (1). Such protein machines undergo motor-like rotational motion (like F 1 -ATPase), carry cargos (like kinesin), or fold proteins (like GroEL, the subject of this paper). An important feature of all ATP-driven molecular machines is a functional cycle that involves sequential transitions between several conformational states (2). Understanding the dynamics of conformational cycling is, therefore, essential for the full elucidation of the mechanism of action of a protein machine.The Escherichia coli molecular chaperone GroEL is a machine that assists protein folding by undergoing a series of allosteric transitions that facilitate protein substrate binding and release (3,4). GroEL is made up of two homoheptameric rings, stacked back-to-back, with a cavity at each end (5), in which protein folding can take place. The allosteric transitions of GroEL are induced by ATP binding that occurs with positive cooperativity within rings and negative cooperativity between rings (6). It has been suggested that the intraring positive cooperativity is an outcome of a concerted switch between two conformations, Tand R, with low and high affinities for ATP, respectively. GroEL functions in conjunction with a heptameric ring-shaped cochaperonin, GroES. Binding of GroES to the so-called cis ring induces an additional conformational change that leads to the R' conformation and triggers dissociation of bound protein substrate into the cavity (7). The structures of the three relatively stable conformations, T, R, and R', have been determined using x-ray crystallography and electron microscopy (8, 9). It is not known ...

Abstract. Aerosols suspended in the atmosphere interact with solar radiation and clouds, thus change the radiation energy fluxes in the atmospheric column. In this paper we measure changes in the atmospheric temperature profile as a function of the smoke loading and the cloudiness, over the Amazon basin, during the dry seasons (August and September) of [2005][2006][2007][2008]. We show that as the aerosol optical depth (AOD) increases from 0.02 to a value of ∼0.6, there is a decrease of ∼4 • C at 1000 hPa, and an increase of ∼1.5 • C at 850 hPa. The warming of the aerosol layer at 850 hPa is likely due to aerosol absorption when the particles are exposed to direct illumination by the sun. The large values of cooling in the lower layers could be explained by a combination of aerosol extinction of the solar flux in the layers aloft together with an aerosol-induced increase of cloud cover which shade the lower atmosphere. We estimate that the increase in cloud fraction due to aerosol contributes about half of the observed cooling in the lower layers.

Aerosols absorb solar radiation thus changing the atmospheric temperature profile but the overall magnitude of this effect is not known. To that end, Saharan dust emissions over the Atlantic Ocean provide an opportunity to examine aerosol‐related heating via satellite imaging. A major difficulty, however, is disentangling a straightforward heating signal caused by the absorbing dust from a meteorological signal, which originates from correlation between dust concentration and air temperature. To tackle the problem, we combine temperature (T) soundings, from the atmospheric infrared sounder (AIRS), with aerosol optical depth (τ) measurements, from the moderate resolution imaging spectroradiometer (MODIS), and data assimilation results from the global data assimilation system (GDAS). We introduce the quantity β(P) ≡ ∂TP/∂τ, the subscript indicating temperature at a given pressure, and study the observed (AIRS) vs. modeled (GDAS) vertical profiles of β(P). Using the vertical as well as horizontal patterns of β(P) and Δβ(P) ≡ βobs. − βmodl., we avoid instrumental and geographic artifacts and extract a remarkably robust radiative heating signal of about 2–4 K within the dust layer. The extracted signal peaks over the mid‐Atlantic Ocean, as a result of competing trends: “memory” of the dust source in the east, and mixing with transparent aerosol in the west.