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 High-Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP) and the new Global Hawk airborne platform that allows long endurance sampling of hurricanes. Supporting data from the High-Altitude Monolithic Microwave Integrated Circuit (MMIC) Sounding Radiometer (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 being formed and maintained through a combination of two main processes: 1) convergence generated from counterrotating mesovortex circulations and the larger vortex-scale flow and 2) the turbulent (scales of ~25 km) transport of anomalously warm, buoyant air from the eye to the eyewall at 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.

Stratospheric injections of carbonaceous aerosols and combustion gases by extreme wildfires have become increasingly common. Recent “megafires,” particularly large and intense fires, delivered particulate burdens to the lower stratosphere comparable to those of moderate volcanic eruptions. The 2017 Canadian megafire generated four large Pyrocumulonimbi (pyroCbs), injecting up to ≈0.3 Tg of smoke in the lower stratosphere. Even more extreme, the 2019/2020 Australian event produced a pyroCb activity resulting in stratospheric smoke intrusions of ≈1 Tg. To understand their contrasting behavior, we present global climate simulations of the atmospheric response to these events, applying smoke burdens informed by remote observations. Model outcomes, compared to satellite data of smoke transport, reproduce reasonably well the initial plume rise, at 0.2–0.3 km/day, attaining heights of ≈20 km in Canada and above 30 km in Australia. Global dispersal of the plume occurs within about 3 weeks in both cases, consistent with observations. Smoke removal timescales, ≈5 months for the Canadian megafire, agree with remote measurements. During the Australian megafire, observations indicate stratospheric injections three times as large, and models predict comparatively longer smoke lifetimes, ≈16 months. After the latter event, atmospheric optical depths and radiative cooling achieved values close to those measured following the Pinatubo eruption. Sensitivity tests of model assumptions indicate, in accord with prior studies, that smoke burden, injection heights, and black carbon content can determine plume evolution and possible climate impacts. An empirical relation between peak heights of stratospheric plumes and lifetimes is derived that can help assess megafire impacts on the stratosphere, climate and the Earth system.

The structure of coherent turbulence in an eyewall replacement cycle in Hurricane Rita (2005) is presented from novel airborne Doppler radar observations using the Imaging Wind and Rain Airborne Profiler (IWRAP). The IWRAP measurements and three-dimensional (3D) wind vector calculations at a grid spacing of 250 m in the horizontal and 30 m in the vertical reveal the ubiquitous presence of organized turbulent eddies in the lower levels of the storm. The data presented here, and the larger collection of IWRAP measurements, currently are the highest-resolution Doppler radar 3D wind vectors ever obtained in a hurricane over the open ocean. Coincident data from NOAA airborne radars, the Stepped Frequency Microwave Radiometer, and flight-level data help to place the IWRAP observations into context and provide independent validation. The typical characteristics of the turbulent eddies are the following: radial wavelengths of ~1–3 km (mean value is ~2 km), depths from the ocean surface up to flight level (~1.5 km), aspect ratio of ~1.3, and horizontal wind speed perturbations of 10–20 m s−1. The most intense eddy activity is located on the inner edge of the outer eyewall during the concentric eyewall stage with a shift to the inner eyewall during the merging stage. The evolving structure of the vertical wind shear is connected to this shift and together these characteristics have several similarities to boundary layer roll vortices. However, eddy momentum flux analysis reveals that high-momentum air is being transported upward, in contrast with roll vortices, with large positive values (~150 m2 s−2) found in the turbulent filaments. In the decaying inner eyewall, elevated tangential momentum is also being transported radially outward to the intensifying outer eyewall. These results indicate that the eddies may have connections to potential vorticity waves with possible modifications due to boundary layer shear instabilities.

Despite the fact that latent heating in cloud systems drives many atmospheric circulations, including tropical cyclones, little is known of its magnitude and structure, largely because of inadequate observations. In this work, a reasonably high-resolution (2 km), four-dimensional airborne Doppler radar retrieval of the latent heat of condensation/evaporation is presented for rapidly intensifying Hurricane Guillermo (1997). Several advancements in the basic retrieval algorithm are shown, including 1) analyzing the scheme within the dynamically consistent framework of a numerical model, 2) identifying algorithm sensitivities through the use of ancillary data sources, and 3) developing a precipitation budget storage term parameterization. The determination of the saturation state is shown to be an important part of the algorithm for updrafts of ~5 m s−1 or less. The uncertainties in the magnitude of the retrieved heating are dominated by errors in the vertical velocity. Using a combination of error propagation and Monte Carlo uncertainty techniques, biases are found to be small, and randomly distributed errors in the heating magnitude are ~16% for updrafts greater than 5 m s−1 and ~156% for updrafts of 1 m s−1. Even though errors in the vertical velocity can lead to large uncertainties in the latent heating field for small updrafts/downdrafts, in an integrated sense the errors are not as drastic. In Part II, the impact of the retrievals is assessed by inserting the heating into realistic numerical simulations at 2-km resolution and comparing the generated wind structure to the Doppler radar observations of Guillermo.

This study investigates the asymmetric distribution of hurricane boundary layer height scales in a storm-motion-relative framework using global positioning system (GPS) dropsonde observations. Data from a total of 1916 dropsondes collected within four times the radius of maximum wind speed of 37 named hurricanes over the Atlantic basin from 1998 to 2015 are analyzed in the composite framework. Motion-relative quadrant mean composite analyses show that both the kinematic and thermodynamic boundary layer height scales tend to increase with increasing radius in all four motion-relative quadrants. It is also found that the thermodynamic mixed layer depth and height of maximum tangential wind speed are within the inflow layer in all motion-relative quadrants. The inflow layer depth and height of the maximum tangential wind are both found to be deeper in the two front quadrants, and they are largest in the right-front quadrant. The difference in the thermodynamic mixed layer depth between the front and back quadrants is smaller than that in the kinematic boundary layer height. The thermodynamic mixed layer is shallowest in the right-rear quadrant, which may be due to the cold wake phenomena. The boundary layer height derived using the critical Richardson number ( $R_{ic}$ ) method shows a similar front-back asymmetry as the kinematic boundary layer height.

The fluid mechanics of hurricanes strongly depends on boundary layer energetics due to the warm-core nature of the system with peak velocities located at lower levels. One barrier that has inhibited a more complete characterization of energy transfer in the boundary layer is a lack of observations that resolve large, turbulent eddies. In particular, the occurrence and structure of upscale energy transfer (backscatter) in the hurricane boundary layer as well as the effects of backscatter on the vortex intensity are unknown. The analysis presented here of very high-resolution, three-dimensional wind observations from Hurricane Rita (2005) at peak intensity reveals large regions of organized backscatter in the boundary layer associated with coherent, turbulent eddies. Strong forwardscatter is also found next to the backscatter regions due to the interaction between adjacent eddies. Two components of the stress tensor are primarily responsible for this alternating scatter structure, as shown by large correlation coefficients between the fields: the radial–vertical component () with average correlations of 79 % and 49 %, respectively. The Leonard, Reynolds and cross-term stress components are also provided. The impact of the sub-filter-scale energy transfer is estimated by computing the kinetic energy budget for the resolved-scale and eddy-scale motions. The results show that the sub-filter-scale energy transfer term is of the same order as the other terms in the eddy-scale budgets, contributing between 16 % and 40 % to the local time tendency with an average contribution of approximately 30 %. These results indicate that the coherent turbulent eddies can affect the vortex dynamics through wave–wave nonlinear interactions, which can subsequently influence the wave–mean flow interactions. This is the first study to examine the full sub-filter-scale energy transfer and its impact on the kinetic energy budget in the hurricane boundary layer. These findings emphasize the importance of coherent turbulence in the energy cascade and have the potential to improve turbulence closure schemes used in numerical simulations.