In the upper troposphere and lower stratosphere (UTLS), large-scale anticyclones associated with monsoons play major roles in tropospheric and stratospheric transport and mixing. To understand the forcing of the North American monsoon anticyclone (NAMA), this study examines the connection between precipitation over the tropics and subtropics of the North American longitude sector and the variability of the troposphere and lower stratosphere. Using ERA5 reanalysis and outgoing longwave radiation (OLR) data from 1979âĂŞ2019, we assess the relationship at the intraseasonal time scale using pentad-mean time series. We show that OLR anomalies are correlated with circulation anomalies northwest and northeast of the region of precipitation. Decreased OLR (increased precipitation) corresponds to increased geopotential heights and anticyclonic circulation anomalies in the 300 - 100 hPa layer and an opposite response in the lower tropospheric 850 - 600 hPa layer. The results are consistent with the established theory of the Rossby wave response to latent heating. The increase in height, which is strongest near 150 hPa, indicates that increased precipitation is associated with a strengthened NAMA. UTLS temperatures also have significant correlations with OLR, with cold (warm) anomalies occurring above (below) the core of the anticyclonic anomaly consistent with large-scale balance. The vertical structure of geopotential and temperature anomalies is compared to simulations using an idealized general circulation model, which shows that such a vertical structure is a consistent response to diabatic heating. Correlations at the interannual time scale resemble those at the intraseasonal time scale, demonstrating that precipitation is related to the NAMA at both time scales.

The Asian monsoon anticyclone (AMA), which is primarily driven by the latent heat released by monsoon precipitation, is one of the dominant features of the Northern Hemisphere summer circulation in the upper troposphere and lower stratosphere. Due to variations in the diabatic heating, interactions with Rossby waves propagating along the subtropical jet, and internal dynamics within the anticyclone, the circulation of the AMA is unsteady. Here we use the ERA-Interim dataset and trajectories computed with ERA-Interim winds to show that the AMA contains two or three distinct synoptic-scale subvortices 69% of the time, while a single circulation center is present only 23% of the time. More than three simultaneous subvortices are uncommon. Observed behaviors of the subvortices include 1) splitting of a single vortex into two vortices; 2) merger of two vortices into a single vortex; 3) vortex shedding in the eastward direction; 4) vortex shedding in the westward direction; and 5) formation, movement, and dissipation of a vortex. The evolution of the subvortices is closely tied to stirring and transport.

Deep convection, as used in meteorology, refers to the rapid ascent of air parcels in the Earth's troposphere driven by the buoyancy generated by phase change in water. Deep convection undergirds some of the Earth's most important and violent weather phenomena and is responsible for many aspects of the observed distribution of energy, momentum, and constituents (particularly water) in the Earth's atmosphere. Deep convection driven by buoyancy generated by the radiative heating of atmospheric dust may be similarly important in the atmosphere of Mars but lacks a systematic description. Here we propose a comprehensive framework for this phenomenon of dusty deep convection (DDC) that is supported by energetic calculations and observations of the vertical dust distribution and exemplary dusty deep convective structures within local, regional, and global dust storm activity. In this framework, DDC is distinct from a spectrum of weaker dusty convective activity because DDC originates from pre-existing or concurrently forming mesoscale circulations that generate high surface dust fluxes, oppose large-scale horizontal advective-diffusive processes, and are thus able to maintain higher dust concentrations than typically simulated. DDC takes two distinctive forms. Mesoscale circulations that form near Mars's highest volcanoes in dust storms of all scales can transport dust to the base of the upper atmosphere in as little as two hours. In the second distinctive form, mesoscale circulations at low elevations within regional and global dust storm activity generate freely convecting streamers of dust that are sheared into the middle atmosphere over the diurnal cycle.

Cloud droplet relative dispersion, defined as the standard deviation over the mean cloud droplet size, is of central importance in determining and understanding aerosol indirect effects. In recent work, it was found that cloud droplet size distributions become broader as a result of supersaturation variability and that the sensitivity of this effect is inversely related to cloud droplet number density. The subject is investigated in further detail using an extensive dataset from a laboratory cloud chamber capable of producing steady-state turbulence. An extended stochastic theory is found to successfully describe properties of the droplet size distribution, including an analytical expression for the relative dispersion. The latter is found to depend on the cloud droplet removal time, which in turn increases with the cloud droplet number density. The results show that relative dispersion decreases monotonically with increasing droplet number density, consistent with some recent atmospheric observations. Experiments spanning fast to slow microphysics regimes are reported. The observed dispersion is used to estimate time scales for autoconversion, demonstrating the important role of the turbulence-induced broadening effect on precipitation development. An initial effort is made to extend the stochastic theory to an atmospheric context with a steady updraft, for which autoconversion time is the controlling factor for droplet lifetime. As in the cloud chamber, relative dispersion is found to increase with decreasing cloud droplet number density.

We use 3-D cloud-resolving model (CRM) simulations of two mesoscale convective systems at mid-latitudes and a simple statistical ensemble method to diagnose the scale dependency of convective momentum transport (CMT) and CMT-related properties, and evaluate a parameterization scheme for convection-induced pressure gradient (CIPG) developed by Gregory et al. (GKI97). GKI97 relates CIPG to a constant coefficient multiplied by mass flux and vertical mean wind shear. CRM results show that mass fluxes and CMT exhibit strong scale dependency in temporal evolution and vertical structure. The prevalent understandings of CMT characteristics in terms of upgradient/downgradient transport are applicable to updrafts but not downdrafts across a wide range of grid spacings (4-512 km). For the small-to-median grid spacings (4~64 km), GKI97 reproduces some aspects of CIPG scale dependency except for underestimating the variations of CIPG as grid spacing decreases. However, for large grid spacings (128~512 km), GKI97 might even less adequately parameterize CIPG because it omits the contribution from either the nonlinear shear or buoyancy forcings. Further diagnosis of CRM results suggests that inclusion of nonlinear shear forcing in GKI97 is needed for the large grid spacings, and use of the three-updraft and one downdraft approach proposed in an earlier study may help a modified GKI97 capture more variations of CIPG as grid spacing decreases for the small-to-median grid spacings. Further, the optimal coefficients used in GKI97 seems insensitive to grid spacings, but they might be different for updrafts and downdrafts, for different MCS types, and for zonal and meridional components.

During the 2012 deployment of the NASA Hurricane and Severe Storm Sentinel (HS3) field campaign, several flights were dedicated to investigating Hurricane Nadine. Hurricane Nadine developed in close proximity to the dust-laden Saharan Air Layer, and is the fourth longest-lived Atlantic hurricane on record, experiencing two strengthening and weakening periods during its 22-day total lifecycle as a tropical cyclone. In this study, the NASA GEOS-5 atmospheric general circulation model and data assimilation system was used to simulate the impacts of dust during the first intensification and weakening phases of Hurricane Nadine using a series of GEOS-5 forecasts initialized during Nadine's intensification phase (12 September 2012). The forecasts explore a hierarchy of aerosol interactions within the model: no aerosol interaction, aerosol-radiation interactions, and aerosol-radiation and aerosol-cloud interactions simultaneously, as well as variations in assumed dust optical properties. When only aerosolradiation interactions are included, Nadine's track exhibits sensitivity to dust shortwave absorption, as a more absorbing dust introduces a shortwave temperature perturbation that impacts Nadine's structure and steering flow, leading to a northward track divergence after 5 days of simulation time. When aerosol-cloud interactions are added, the track exhibits little sensitivity to dust optical properties. This result is attributed to enhanced longwave atmospheric cooling from clouds that counters shortwave atmospheric warming by dust surrounding Nadine, suggesting that aerosol-cloud interactions are a more significant influence on Nadine's track than aerosol-radiation interactions. These findings demonstrate that tropical systems, specifically their track, can be impacted by dust interaction with the atmosphere.

The treatment of strongly anisotropic scattering phase functions is still a challenge for accurate radiance computations. The new Delta-M+ method resolves this problem by introducing a reliable, fast, accurate, and easy-to-use Legendre expansion of the scattering phase function with modified moments. Delta-M+ is an upgrade of the widely-used Delta-M method that truncates the forward scattering peak with a Dirac delta function, where the '+' symbol indicates that it essentially matches moments beyond the first terms. Compared with the original Delta-M method, Delta-M+ has the same computational efficiency, but for radiance computations the accuracy and stability have been increased dramatically.

This study uses eddy-permitting simulations to investigate the mechanisms that promote mesoscale variability of moisture in drizzling stratocumulus-topped marine boundary layers. Simulations show that precipitation tends to increase horizontal scales. Analysis of terms in the prognostic equation for total water mixing ratio variance indicates that moisture stratification plays a leading role in setting horizontal scales. This result is supported by simulations in which horizontal mean thermodynamic profiles are strongly nudged to their initial well-mixed state, which limits cloud scales. It is found that the spatial variability of sub-cloud moist cold pools surprisingly tends to respond to, rather than determine, the mesoscale variability, which may distinguish them from dry cold pools associated with deeper convection. Simulations also indicate that moisture stratification increases cloud scales specifically by increasing latent heating within updrafts, which increases updraft buoyancy and favors greater horizontal scales.

Using an idealized model framework with high-frequency tropical latent heating variability derived from global satellite observations of precipitation and clouds, the authors examine the properties and effects of gravity waves in the lower stratosphere, contrasting conditions in an El Niño year and a La Niña year. The model generates a broad spectrum of tropical waves including planetary-scale waves through mesoscale gravity waves. The authors compare modeled monthly mean regional variations in wind and temperature with reanalyses and validate the modeled gravity waves using satellite- and balloon-based estimates of gravity wave momentum flux. Some interesting changes in the gravity spectrum of momentum flux are found in the model, which are discussed in terms of the interannual variations in clouds, precipitation, and large-scale winds. While regional variations in clouds, precipitation, and winds are dramatic, the mean gravity wave zonal momentum fluxes entering the stratosphere differ by only 11%. The modeled intermittency in gravity wave momentum flux is shown to be very realistic compared to observations, and the largest-amplitude waves are related to significant gravity wave drag forces in the lowermost stratosphere. This strong intermittency is generally absent or weak in climate models because of deficiencies in parameterizations of gravity wave intermittency. These results suggest a way forward to improve model representations of the lowermost stratospheric quasi-biennial oscillation winds and teleconnections.

Expansive cirrus clouds present above the anvils of extratropical convection have been observed in satellite and aircraft-based imagery for several decades. Despite knowledge of their occurrence, the precise mechanisms and atmospheric conditions leading to their formation and maintenance are not entirely known. Here, the formation of these cirrus "plumes" is examined using a combination of satellite imagery, four-dimensional ground-based radar observations, assimilated atmospheric states from a state-of-the-art reanalysis, and idealized numerical simulations with explicitly resolved convection. Using data from 20 recent events (2013-present), it is found that convective cores of storms with above-anvil cirrus plumes reach altitudes 1-6 km above the tropopause. Thus, it is likely that these clouds represent the injection of cloud material into the lower stratosphere. Comparison of storms with above-anvil cirrus plumes and observed tropopause-penetrating convection without plumes reveals an association with large vector differences between the motion of a storm and the environmental wind in the upper troposphere and lower stratosphere (UTLS), suggesting that gravity wave breaking and/or stretching of the tropopause-penetrating cloud are/is more prevalent in plume-producing storms. A weak relationship is found between plume occurrence and the stability of the lower stratosphere (or tropopause structure), and no relationship is found with the duration of stratospheric penetration or stratospheric humidity. Idealized model simulations of tropopause-penetrating convection with small and large magnitudes of storm-relative wind in the UTLS are found to reproduce the observationally established storm-relative wind relationship and show that frequent gravity wave breaking is the primary mechanism responsible for plume formation.

Dust storms are Mars's most notable meteorological phenomenon, but many aspects of their structure and dynamics remain mysterious. The cloud-top appearance of dust storms in visible imagery varies on a continuum between diffuse/hazy and textured. Textured storms contain cellular structure and/or banding, which is thought to indicate active lifting within the storm. Some textured dust storms may contain the deep convection that generates the detached dust layers observed high in Mars's atmosphere. This study focuses on textured, local dust storms in a limited area within NE Amazonis and SW Arcadia Planitiae (25°-40° N,155°-165° W) using collocated observations by instruments on board the Mars Global Surveyor (MGS) and Mars Reconnaissance Orbiter (MRO) satellites. In northern fall and winter, this area frequently experiences dust storms with a previously unreported ruffled texture that resembles wide, mixed-layer rolls in the Earth's atmosphere, a resemblance that is supported by high resolution active sounding and passive radiometry in both the near and thermal infrared. These storms are mostly confined within the atmospheric boundary layer and are rarely sources of detached dust layers. The climatology and structure of these storms is thus consistent with an underlying driver of cold air advection events related to the passage of strong baroclinic waves. While the properties of the studied region may be ideal for detecting these structures and processes, the dynamics here are likely relevant to dust storm activity elsewhere on Mars.

The evolution of rapidly intensifying Hurricane Karl (2010) is examined from a suite of remote sensing observations during the NASA Genesis and Rapid Intensification Processes (GRIP) field experiment. The novelties of this study are in the analysis of data from the airborne Doppler radar HIWRAP and the new Global Hawk airborne platform that allows long endurance sampling of hurricanes. Supporting data from the HAMSR microwave sounder coincident with HIWRAP and coordinated flights with the NOAA WP-3D aircraft help to provide a comprehensive understanding of the storm. The focus of the analysis is on documenting and understanding the structure, evolution and role of small scale, deep convective forcing in the storm intensification process. Deep convective bursts are sporadically initiated in the downshear quadrants of the storm and rotate into the upshear quadrants for a period of ~ 12 h during the rapid intensification. The aircraft data analysis indicates that the bursts are forming through a combination of two main processes: (1) convergence generated from counter-rotating mesovortex circulations and the larger scale flow and (2) the turbulent transport of warm, buoyant air from the eye to the eyewall at mid-to-low levels. The turbulent mixing across the eyewall interface and forced convective descent adjacent to the bursts assists in carving out the eye of Karl, which leads to an asymmetric enhancement of the warm core. The mesovortices play a key role in the evolution of the features described above. The Global Hawk aircraft allowed an examination of the vortex response and axisymmetrization period in addition to the burst pulsing phase. A pronounced axisymmetric development of the vortex is observed following the pulsing phase that includes a sloped eyewall structure and formation of a clear, wide eye.

Reactive nitrogen emissions into the atmosphere are increasing due to human activities, affecting nitrogen deposition to the surface and impacting the productivity of terrestrial and marine ecosystems. An atmospheric chemistry-transport model (TM4-ECPL) is here used to calculate the global distribution of total nitrogen deposition, accounting for the first time for both its inorganic and organic fractions in gaseous and particulate phases, and past and projected changes due to anthropogenic activities. The anthropogenic and biomass burning ACCMIP historical and RCP6.0 and RCP8.5 emissions scenarios are used. Accounting for organic nitrogen (ON) primary emissions, the present-day global nitrogen atmospheric source is about 60% anthropogenic, while total N deposition increases by about 20% relative to simulations without ON primary emissions. About 20-25% of total deposited N is ON. About 10% of the emitted nitrogen oxides are deposited as ON instead of inorganic nitrogen (IN) as is considered in most global models. Almost a 3-fold increase over land (2-fold over the ocean) has been calculated for soluble N deposition due to human activities from 1850 to present. The investigated projections indicate significant changes in the regional distribution of N deposition and chemical composition, with reduced compounds gaining importance relative to oxidized ones, but very small changes in the global total flux. Sensitivity simulations quantify uncertainties due to the investigated model parameterizations of IN partitioning onto aerosols and of N chemically fixed on organics to be within 10% for the total soluble N deposition and between 25-35% for the dissolved ON deposition. Larger uncertainties are associated with N emissions.

Column water vapor (CWV) is studied using data from the Dynamics of the Madden-Julian Oscillation (DYNAMO) field experiment. A distinctive moist mode in tropical CVW probability distributions motivates the work. The Lagrangian CWV tendency (LCT) leaves together the compensating tendencies from phase change and vertical advection, quantities which cannot be measured accurately by themselves, to emphasize their small residual, which governs evolution. The slope of LCT vs. CWV suggests that the combined effects of phase changes and vertical advection act as a robust positive feedback on CWV variations, while evaporation adds a broadscale positive tendency. Analyzed diabatic heating profiles become deeper and stronger as CWV increases. Stratiform heating is found to accompany Lagrangian drying at high CWV, but its association with deep convection makes the mean LCT positive at high CWV. Lower-tropospheric wind convergence is found in high-CVW airmasses, acting to shrink their area in time. When ECMWF heating profile indices and S-POL and TRMM radar data are binned jointly by CWV and LCT, bottom-heavy heating associated with shallow and congestus convection is found in columns transitioning through Lagrangian moistening into the humid, high-rainrate mode of the CWV distribution near 50-55mm, while non-raining columns and columns with widespread stratiform precipitation are preferentially associated with Lagrangian drying. Interpolated sounding-array data produce substantial errors in LCT budgets, because horizontal advection is inaccurate without satellite input to constrain horizontal gradients.

The use of ensemble-average values of aspect ratio and distortion parameter of hexagonal ice prisms for the estimation of ensemble-average scattering asymmetry parameters is evaluated. Using crystal aspect ratios greater than unity generally leads to ensemble-average values of aspect ratio that are inconsistent with the ensemble-average asymmetry parameters. When a definition of aspect ratio is used that limits the aspect ratio to below unity () for both hexagonal plates and columns, the effective asymmetry parameters calculated using ensemble-average aspect ratios are generally consistent with ensemble-average asymmetry parameters, especially if aspect ratios are geometrically averaged. Ensemble-average distortion parameters generally also yield effective asymmetry parameters that are largely consistent with ensemble-average asymmetry parameters. In the case of mixtures of plates and columns, it is recommended to geometrically average the aspect ratios and to subsequently calculate the effective asymmetry parameter using a column or plate geometry when the contribution by columns to a given mixture's total projected area is greater or lower than 50%, respectively. In addition, we show that ensemble-average aspect ratios, distortion parameters and asymmetry parameters can generally be retrieved accurately from simulated multi-directional polarization measurements based on mixtures of varying columns and plates. However, such retrievals tend to be somewhat biased toward yielding column-like aspect ratios. Furthermore, generally large retrieval errors can occur for mixtures with approximately equal contributions of columns and plates and for ensembles with strong contributions of thin plates.

A novel model for the variability in aerosol optical thickness (AOT) is presented. This model is based on the consideration of AOT fields as realizations of a stochastic process, that is the exponent of an underlying Gaussian process with a specific autocorrelation function. In this approach AOT fields have lognormal PDFs and structure functions having the correct asymptotic behavior at large scales. The latter is an advantage compared with fractal (scale-invariant) approaches. The simple analytical form of the structure function in the proposed model facilitates its use for the parameterization of AOT statistics derived from remote sensing data. The new approach is illustrated using a year-long global MODIS AOT dataset (over ocean) with 10 km resolution. It was used to compute AOT statistics for sample cells forming a grid with 5° spacing. The observed shapes of the structure functions indicated that in a large number of cases the AOT variability is split into two regimes that exhibit different patterns of behavior: small-scale stationary processes and trends reflecting variations at larger scales. The small-scale patterns are suggested to be generated by local aerosols within the marine boundary layer, while the large-scale trends are indicative of elevated aerosols transported from remote continental sources. This assumption is evaluated by comparison of the geographical distributions of these patterns derived from MODIS data with those obtained from the GISS GCM. This study shows considerable potential to enhance comparisons between remote sensing datasets and climate models beyond regional mean AOTs.