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Papers by Robert Rogers

Monthly Weather Review, Apr 1, 2017

Journal of the Atmospheric Sciences, May 1, 2021

This study investigates the precipitation symmetrization preceding rapid intensification (RI) of ... more This study investigates the precipitation symmetrization preceding rapid intensification (RI) of tropical cyclones (TCs) experiencing vertical wind shear by analyzing numerical simulations of Typhoon Mujigae (2015) with warm (CTL) and relatively cool (S1) sea surface temperatures (SSTs). A novel finding is that precipitation symmetrization is maintained by the continuous development of deep convection along the inward flank of a convective precipitation shield (CPS), especially in the downwind part. Beneath the CPS, downdrafts flush the boundary layer with low-entropy parcels. These low-entropy parcels do not necessarily weaken the TCs; instead, they are ''recycled'' in the TC circulation, gradually recovered by positive enthalpy fluxes, and develop into convection during their propagation toward a downshear convergence zone. Along-trajectory vertical momentum budget analyses reveal the predominant role of buoyancy acceleration in the convective development in both experiments. The boundary layer recovery is more efficient for warmer SST, and the stronger buoyancy acceleration accounts for the higher probability of these parcels developing into deep convection in the downwind part of the CPS, which helps maintain the precipitation symmetrization in CTL. In contrast, less efficient boundary layer recovery and less upshear deep convection hinder the precipitation symmetrization in S1. These findings highlight the key role of boundary layer recovery in regulating the precipitation symmetrization and upshear deep convection, which further accounts for an earlier RI onset timing of the CTL TC. The inward-rebuilding pathway also illuminates why deep convection is preferentially located inside the radius of maximum wind of sheared TCs undergoing RI.

Encyclopedia of Hydrological Sciences, Dec 15, 2009

Page 1. Tropical Cyclone Rainfall ROBERT ROGERS1, FRANK MARKS1 AND TIMOTHY MARCHOK2 1NOAA/AOML Hu... more Page 1. Tropical Cyclone Rainfall ROBERT ROGERS1, FRANK MARKS1 AND TIMOTHY MARCHOK2 1NOAA/AOML Hurricane Research Division, Miami, FL, USA 2NOAA Geophysical Fluid Dynamics Laboratory, Princeton University Forrestal Campus, Princeton, NJ, USA ...

This review prepared for the fourth International Workshop on Tropical Cyclone Landfall Processes... more This review prepared for the fourth International Workshop on Tropical Cyclone Landfall Processes (IWTCLP-4) summarizes the most recent (2015-2017) theoretical and practical knowledge in the field of tropical cyclone (TC) track, intensity, and structure rapid changes at or near landfall. Although the focus of IWTCLP-IV was on landfall, this summary necessarily embraces the characteristics of storms during their course over the ocean prior to and leading up to landfall. In the past few years, extremely valuable observational datasets have been collected using both aircraft reconnaissance and new geostationary and low-earth orbiting satellites at high temporal and spatial resolution for TC forecasting guidance and research studies. Track deflections for systems near complex topography such as that of Taiwan and La Reunion have been further investigated, and advanced numerical models with high spatial resolution necessary to predict the interaction of the TC circulation with steep isla...

Atmosphere, 2020

This paper reviews the evolution of planetary boundary layer (PBL) parameterization schemes that ... more This paper reviews the evolution of planetary boundary layer (PBL) parameterization schemes that have been used in the operational version of the Hurricane Weather Research and Forecasting (HWRF) model since 2011. Idealized simulations are then used to evaluate the effects of different PBL schemes on hurricane structure and intensity. The original Global Forecast System (GFS) PBL scheme in the 2011 version of HWRF produces the weakest storm, while a modified GFS scheme using a wind-speed dependent parameterization of vertical eddy diffusivity (Km) produces the strongest storm. The subsequent version of the hybrid eddy diffusivity and mass flux scheme (EDMF) used in HWRF also produces a strong storm, similar to the version using the wind-speed dependent Km. Both the intensity change rate and maximum intensity of the simulated storms vary with different PBL schemes, mainly due to differences in the parameterization of Km. The smaller the Km in the PBL scheme, the faster a storm tends ...

Monthly Weather Review, 2020

The spatial and temporal variation in multiscale structures during the rapid intensification of H... more The spatial and temporal variation in multiscale structures during the rapid intensification of Hurricane Michael (2018) are explored using a coupled atmospheric–oceanic dataset obtained from NOAA WP-3D and G-IV aircraft missions. During Michael’s early life cycle, the importance of ocean structure is studied to explore how the storm intensified despite experiencing moderate vertical shear. Michael maintained a fairly symmetric precipitation distribution and resisted lateral mixing of dry environmental air into the circulation upshear. The storm also interacted with an oceanic eddy field leading to cross-storm sea surface temperature (SST) gradients of ~2.5°C. This led to the highest enthalpy fluxes occurring left of shear, favoring the sustainment of updrafts into the upshear quadrants and a quick recovery from low-entropy downdraft air. Later in the life cycle, Michael interacted with more uniform and higher SSTs that were greater than 28°C, while vertical shear imposed asymmetrie...

Journal of the Atmospheric Sciences, 2019

Operational numerical models failed to predict the record-setting rapid intensification and rapid... more Operational numerical models failed to predict the record-setting rapid intensification and rapid overwater weakening of Hurricane Patricia (2015) in the eastern North Pacific basin, resulting in large intensity forecast errors. In an effort to better understand the mesoscale processes contributing to Patricia’s rapid intensity changes, we analyze high-resolution aircraft observations collected on 22–23 October. Spline-based variational analyses are created from observations collected via in situ measurements, Doppler radar, and full-tropospheric dropsonde profiles as part of the Office of Naval Research Tropical Cyclone Intensity (TCI) experiment and the National Oceanic and Atmospheric Administration Intensity Forecasting Experiment (IFEX). We present the first full-tropospheric calculation of the dry, axisymmetric Ertel’s potential vorticity (PV) in a tropical cyclone without relying on balance assumptions. Detailed analyses reveal the formation of a “hollow tower” PV structure a...

Monthly Weather Review, 2018

Hurricane Bonnie (1998) was an unusually resilient hurricane that maintained a steady-state inten... more Hurricane Bonnie (1998) was an unusually resilient hurricane that maintained a steady-state intensity while experiencing strong (12–16 m s−1) vertical wind shear and an eyewall replacement cycle. This remarkable behavior was examined using observations from flight-level data, microwave imagery, radar, and dropsondes over the 2-day period encompassing these events. Similar to other observed eyewall replacement cycles, Bonnie exhibited the development, strengthening, and dominance of a secondary eyewall while a primary eyewall decayed. However, Bonnie’s structure was highly asymmetric because of the large vertical wind shear, in contrast to the more symmetric structures observed in other hurricanes undergoing eyewall replacement cycles. It is hypothesized that the unusual nature of Bonnie’s evolution arose as a result of an increase in vertical wind shear from 2 to 12 m s−1 even as the storm intensified to a major hurricane in the presence of high ambient sea surface temperatures. The...

Monthly Weather Review, 2017

A comprehensive examination of tropical cyclone (TC) kinematic and thermodynamic structure in the... more A comprehensive examination of tropical cyclone (TC) kinematic and thermodynamic structure in the Atlantic basin is created from the Extended Flight Level Dataset for Tropical Cyclones (FLIGHT+, version 1.1). In situ data collected at the 700-hPa flight level by NOAA WP-3D and USAF WC-130 aircraft from 1999 to 2012 are analyzed. A total of 233 azimuthal mean profiles comprising 1498 radial legs are stratified by TC intensity and 12-h intensity change. A matrix of composite structures is created for minor (category 1 and 2) and major (category 3 and above) hurricanes that are intensifying [intensity increase ≥10 kt (12 h)−1], steady state [intensity change between ±5 kt (12 h)−1], and weakening [intensity decrease [Formula: see text] kt (12 h)−1]. Additional considerations to the impacts of age on TC structure are given as well. Axisymmetric radial composites reveal that intensifying TCs have statistically significant structural differences from TCs that are steady state or weakening...

Monthly Weather Review, 2015

As part of the Hurricane Forecast Improvement Project (HFIP), recent boundary layer physics upgra... more As part of the Hurricane Forecast Improvement Project (HFIP), recent boundary layer physics upgrades in the operational Hurricane Weather Research and Forecasting (HWRF) Model have benefited from analyses of in situ aircraft observations in the low-level eyewall region of major hurricanes. This study evaluates the impact of these improvements to the vertical diffusion in the boundary layer on the simulated track, intensity, and structure of four hurricanes using retrospective HWRF forecasts. Structural metrics developed from observational composites are used in the model evaluation process. The results show improvements in track and intensity forecasts in response to the improvement of the vertical diffusion. The results also demonstrate substantial improvements in the simulated storm size, surface inflow angle, near-surface wind profile, and kinematic boundary layer heights in simulations with the improved physics, while only minor improvements are found in the thermodynamic bounda...

Monthly Weather Review, 2000

A simple technique for using radar reflectivity to improve model initialization is presented. Unl... more A simple technique for using radar reflectivity to improve model initialization is presented. Unlike previous techniques, the scheme described here does not infer rain rates and heating profiles from assumed relationships between remotely sensed variables and precipitation rates. Rather, the radar data are only used to tell the model when and where deep moist convection is occurring. This information is then used to activate the model's convective parameterization scheme in the grid elements where convection is observed. This approach has the advantage that the convective precipitation rates and heating profiles generated by the convective parameterization are compatible with the local (grid element) environment. The premise is that if convection is forced to develop when and where it is observed during a data assimilation period, convectively forced modifications to the environment will be in the correct locations at the model initial forecast time and the resulting forecast will be more accurate. Three experiments illustrating how the technique is applied in the simulation of deep convection in a warmseason environment are presented: a control run in which no radar data are assimilated, and two additional runs where radar data are assimilated for 12 h in one run and 24 h in the other. The results indicate that assimilating radar data can improve a model's description of the mesoscale environment during the preforecast time period, thereby resulting in an improved forecast of precipitation and the mesoscale environment.

27th Conference on …, 2006

27th Conference on Hurricanes and Tropical Meteorology 1A.1. Overview of the Field Phase of the N... more 27th Conference on Hurricanes and Tropical Meteorology 1A.1. Overview of the Field Phase of the NASA Tropical Cloud Systems and Processes (TCSP) Experiment. Robbie E. Hood, NASA/MSFC, Huntsville, AL; and E. Zipser ...

Monthly Weather Review, Feb 14, 2020

The initiation of a rapid intensification (RI) event for a tropical cyclone (TC) at major hurrica... more The initiation of a rapid intensification (RI) event for a tropical cyclone (TC) at major hurricane intensity is a rare event in the North Atlantic basin. This study examined the environmental and vortex-scale processes related to such an RI event observed in Hurricane Irma (2017) using a combination of flight-level and airborne radar aircraft reconnaissance observations, microwave satellite observations, and model environmental analyses. The onset of RI was linked to an increase in sea surface temperatures and ocean heat content toward levels more commonly associated with North Atlantic RI episodes. Remarkably, Irma’s RI event comprised two rapidly evolving eyewall replacement cycle (ERC) episodes that each completed in less than 12 h. The two ERC events displayed different secondary eyewall formation (SEF) mechanisms and vortex evolutions. During the first SEF event, a secondary maximum in ascent and tangential wind was observed at the leading edge of a mesoscale descending inflow jet. During the ensuing ERC event, the primary eyewall weakened and ultimately collapsed, resulting in a brief period of weakening. The second SEF event displayed characteristics consistent with unbalanced boundary layer dynamics. Additionally, it is plausible that both SEF events were affected by the stagnation and axisymmeterization of outward-propagating vortex Rossby waves. During the second ERC event, the TC continued to rapidly intensify, which is a stark contrast to the ERC paradigm described in the literature. The differing ERC evolutions appear linked to the vortex response to changing environmental conditions. The results presented here underscore the utility of frequent aircraft reconnaissance observations for an improved understanding of TC dynamics.

Monthly Weather Review, May 3, 2021

As part of the NASA Earth Venture-Instrument program, the Time-Resolved Observations of Precipita... more As part of the NASA Earth Venture-Instrument program, the Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS) mission, to be launched in January 2022, will deliver unprecedented rapid-update microwave measurements over the tropics that can be used to observe the evolution of the precipitation and thermodynamic structure of tropical cyclones (TCs) at meso-and synoptic scales. TROPICS consists of six CubeSats, each hosting a passive microwave radiometer that provides radiance observations sensitive to atmospheric temperature, water vapor, precipitation, and precipitation-sized ice particles. In this study, the impact of TROPICS all-sky radiances on TC analyses and forecasts is explored through a regional mesoscale observing system simulation experiment (OSSE). The results indicate that the TROPICS all-sky radiances can have positive impacts on TC track and intensity forecasts, particularly when some hydrometeor state variables and other state variables of the data assimilation system that are relevant to cloudy radiance assimilation are updated. The largest impact on the model analyses is seen in the humidity fields, regardless of whether or not there are radiances assimilated from other satellites. TROPICS radiances demonstrate large impact on TC analyses and forecasts when other satellite radiances are absent. The assimilation of the all-sky TROPICS radiances without default radiances leads to a consistent improvement in the low-and midtropospheric temperature and wind forecasts throughout the 5-day forecasts, but only up to 36-h lead time in the humidity forecasts at all pressure levels. This study illustrates the potential benefits of TROPICS data assimilation for TC forecasts and provides a potentially streamlined pathway for transitioning TROPICS data from research to operations postlaunch. SIGNIFICANCE STATEMENT: As the Global Observing System evolves, smaller satellites such as CubeSats are emerging as inexpensive alternatives for providing important observations of Earth as compared to traditional satellites. TROPICS, to be launched in January 2022, is one of the NASA CubeSats missions that will deliver unprecedented rapidupdate microwave measurements over the tropics. This study examines the impacts of simulated radiances from the TROPICS constellation of satellites for tropical cyclone analyses and forecasts in a regional mesoscale model and demonstrates the potential benefits of TROPICS data assimilation on TC forecasts. The infrastructure to incorporate the new TROPICS datasets into the operational model that was developed for this study will facilitate a transition from research to operations once the TROPICS data becomes available after the mission launch.

Monthly Weather Review, 2023

This study investigates the relationship between the azimuthally averaged kinematic structure of ... more This study investigates the relationship between the azimuthally averaged kinematic structure of the tropical cyclone boundary layer (TCBL) and storm intensity, intensity change, and vortex structure above the BL. These relationships are explored using composites of airborne Doppler radar vertical profiles, which have a higher vertical resolution than typically used three-dimensional analyses and, therefore, better capture TCBL structure. Results show that the BL height, defined by the depth of the inflow layer, is greater in weak storms than in strong storms. The inflow layer outside the radius of maximum tangential wind speed (RMW) is deeper in intensifying storms than in nonintensifying storms at an early stage. The peak BL convergence inside the RMW is larger in intensifying storms than in nonintensifying storms. Updrafts originating from the TCBL are concentrated near the RMW for intensifying TCs, while updrafts span a large radial range outside the RMW for nonintensifying TCs. In terms of vortex structure above the BL, storms with a quickly decaying radial profile of tangential wind outside the RMW (“narrow” vortices) tend to have a deeper inflow layer outside the RMW, stronger inflow near the RMW, deeper and more concentrated strong updrafts close to the RMW, and weaker inflow in the outer core region than those with a slowly decaying tangential wind profile (“broad” vortices). The narrow TCs also tend to intensify faster than broad TCs, suggesting that a key relationship exists among vortex shape, the BL kinematic structure, and TC intensity change. This relationship is further explored by comparisons of absolute angular momentum budget terms for each vortex shape.

Monthly Weather Review, Apr 1, 2023

As a part of the Tropical Cyclone Rapid Intensification Project (TCRI), observations were made of... more As a part of the Tropical Cyclone Rapid Intensification Project (TCRI), observations were made of the rapid intensification of Hurricane Sally (2020) as it passed over the Gulf of Mexico. High-altitude dropsondes and radar observations from NOAA's Gulfstream IV, radar observations from WP-3D aircraft, the WSR-88D ground radar network, satellite images, and satellite-detected lightning strikes are used to apply recently developed theoretical knowledge about tropical cyclone intensification. As observed in many other tropical cyclones, strong, bottom-heavy vertical mass flux profiles are correlated with low (but positive) values of low-to midlevel moist convective instability along with high column relative humidity. Such mass flux profiles produce rapid spinup at low levels and the environmental conditions giving rise to them are associated with an intense midlevel vortex. This low-level spinup underneath the midlevel vortex results in the vertical alignment of the vortex column, which is a key step in the rapid intensification process. In the case of Sally, the spinup of the low-level vortex resulted from vorticity stretching, while the spinup of the midlevel vortex at 6 km resulted from vorticity tilting produced by the interaction of convective ascent with moderate vertical shear. SIGNIFICANCE STATEMENT: The purpose of this study is to investigate the rapid intensification of Hurricane Sally as it was approaching the Florida Panhandle. We do that by analyzing an unprecedented dataset from the NOAA WP-3D and Gulfstream-IV aircraft, together with ground-based radar and satellite data. We find that both the dynamics (vorticity structure and evolution) and thermodynamics (instability index, saturation fraction, heating/mass flux profiles) need to be considered in diagnosing intensification processes. Further field projects with continuous high-altitude dropsondes and research are needed to see if these are applicable to other reformation events as well as genesis.

Recent technology advances in miniature microwave radiometers that can be hosted on very small sa... more Recent technology advances in miniature microwave radiometers that can be hosted on very small satellites has made possible a new class of affordable constellation missions that provide very high revisit rates of tropical cyclones and other severe weather. The Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS) mission was selected by NASA as part of the Earth Venture-Instrument (EVI-3) program and is now in development with planned launch readiness in late 2019. The overarching goal for TROPICS is to provide nearly all-weather observations of 3-D temperature and humidity, as well as cloud ice and precipitation horizontal structure, at high temporal resolution to conduct high-value science investigations of tropical cyclones (TCs). TROPICS will provide rapid-refresh microwave measurements (median refresh rate better than 60 minutes for the baseline mission) over the tropics that can be used to observe the thermodynamics of the troposphere and precipitation structure for storm systems at the mesoscale and synoptic scale over the entire storm lifecycle. TROPICS will comprise a constellation of at least six CubeSats in three low-Earth orbital planes. Each CubeSat will host a high performance radiometer to provide temperature profiles using seven channels near the 118.75 GHz oxygen absorption line, water vapor profiles using three channels near the 183 GHz water vapor absorption line, imagery in a single channel near 90 GHz for precipitation measurements (when combined with higher resolution water vapor channels), and a single channel at 205 GHz that is more sensitive to precipitation-sized ice particles and low-level moisture. This observing system offers an unprecedented combination of horizontal and temporal resolution in the microwave spectrum to measure environmental and inner-core conditions for TCs on a nearly global scale and is a major leap forward in the temporal resolution of several key parameters needed for assimilation into advanced data assimilation systems capable of utilizing rapid-update radiance or retrieval data. Here, we provide an overview of the mission and an update on current status, with a focus on unique characteristics of the Cubesat system, recent performance simulations on a range of observables to be provided by the constellation, and a summary of science applications.

Monthly Weather Review, Mar 1, 2018

The relationship between radial and azimuthal variations in the composite characteristics of conv... more The relationship between radial and azimuthal variations in the composite characteristics of convective bursts (CBs), that is, regions of the most intense upward motion in tropical cyclones (TCs), and TC intensity change is examined using NOAA P-3 tail Doppler radar. Aircraft passes collected over a 13-yr period are examined in a coordinate system rotated relative to the deep-layer vertical wind shear vector and normalized by the low-level radius of maximum winds (RMW). The characteristics of CBs are investigated to determine how the radial and azimuthal variations of their structures are related to hurricane intensity change. In general, CBs have elevated reflectivity just below the updraft axis, enhanced tangential wind below and radially outward of the updraft, enhanced vorticity near the updraft, and divergent radial flow at the top of the updraft. When examining CB structure by shear-relative quadrant, the downshear-right (upshear left) region has updrafts at the lowest (highest) altitudes and weakest (strongest) magnitudes. When further stratifying by intensity change, the greatest differences are seen upshear. Intensifying storms have updrafts on the upshear side at a higher altitude and stronger magnitude than steady-state storms. This distribution provides a greater projection of diabatic heating onto the azimuthal mean, resulting in a more efficient vortex spinup. For variations based on radial location, CBs located inside the RMW show stronger updrafts at a higher altitude for intensifying storms. Stronger and deeper updrafts inside the RMW can spin up the vortex through greater angular momentum convergence and a more efficient vortex response to the diabatic heating.

Monthly Weather Review, Nov 1, 2017

Prior studies have shown an association between symmetrically distributed precipitation and tropi... more Prior studies have shown an association between symmetrically distributed precipitation and tropical cyclone (TC) intensification. Although environmental vertical wind shear typically forces an asymmetric precipitation distribution in TCs, the magnitude of this asymmetry can exhibit considerable variability, even among TCs that experience similar shear magnitudes. This observational study examines the thermodynamic and kinematic influences on precipitation symmetry in two such cases: Bertha and Cristobal (2014). Consistent with the impact of the shear, both TCs exhibited a tilted vortex as well as a pronounced azimuthal asymmetry, with the maximum precipitation occurring in the downshear-left quadrant. However, Bertha was characterized by more symmetrically distributed precipitation and relatively modest vertical motions, while Cristobal was characterized by more azimuthally confined precipitation and much more vigorous vertical motions. Observations showed three potential hindrances to precipitation symmetry that were more prevalent in Cristobal than in Bertha: (i) convective downdrafts that transported low entropy air downward into the boundary layer, cooling and stabilizing the lower troposphere downstream in the left-of-shear and upshear quadrants; (ii) subsidence in the upshear quadrants, which acted to increase the temperature and decrease the relative humidity of the midtroposphere, resulting in capping of the boundary layer; and (iii) lateral advection of midtropospheric dry air from the environment, which dried the TC's upshear quadrants.

Journal of the Atmospheric Sciences, Aug 6, 2018

Airborne Doppler radar captured the inner core of Hurricane Earl during the early stages of secon... more Airborne Doppler radar captured the inner core of Hurricane Earl during the early stages of secondary eyewall formation (SEF), providing needed insight into the SEF dynamics. An organized rainband complex outside of the primary eyewall transitioned into an axisymmetric secondary eyewall containing a low-level tangential wind maximum. During this transition, the downshear-left quadrant of the storm exhibited several notable features. A mesoscale descending inflow (MDI) jet persistently occurred across broad stretches of stratiform precipitation in a pattern similar to previous studies. This negatively buoyant jet traveled radially inward and descended into the boundary layer. Farther inward, enhanced low-level inflow and intense updrafts appeared. The updraft adjacent to the MDI was likely triggered by a region of convergence and upward acceleration (induced by the negatively buoyant MDI) entering the high-u e boundary layer. This updraft and the MDI in the downshear-left quadrant accelerated the tangential winds in a radial range where the axisymmetric wind maximum of the secondary eyewall soon developed. This same quadrant eventually exhibited the strongest overturning circulation and wind maximum of the forming secondary eyewall. Given these features occurring in succession in the downshear-left quadrant, we hypothesize that the MDI plays a significant dynamical role in SEF. The MDI within a mature rainband complex persistently perturbs the boundary layer, which locally forces enhanced convection and tangential winds. These perturbations provide steady low-level forcing that projects strongly onto the axisymmetric field, and forges the way for secondary eyewall development via one of several SEF theories that invoke axisymmetric dynamical processes.