Christopher Rozoff - Academia.edu (original) (raw)
Papers by Christopher Rozoff
Boundary Layer Meteorology, 2007
The Town Energy Budget (TEB) model, a detailed urban parameterisation using a generalised canyon ... more The Town Energy Budget (TEB) model, a detailed urban parameterisation using a generalised canyon geometry, coupled with the Regional Atmospheric Modelling System (RAMS) is used to simulate the wintertime local circulation in the megacity environment of the metropolitan area of Sao Paulo (MASP) in Brazil. Model simulations are performed using actual topography and land-use fields. Comparison with a simple urban parameterisation based on the LEAF-2 scheme is also shown. Validation is based on comparison between model simulations and observations. Sensitivity tests with TEB reveal an important interaction between the sea breeze and the MASP heat island circulation. Even though topography is known to play an important role in the MASP region’s weather, in these tests the simulations were performed without topography in order to unambiguously identify the interaction between the two local circulations. The urban heat island (UHI) forms a strong convergence zone in the centre of the city and thereby accelerates the sea-breeze front toward the centre of the city. The presence of the urban region increases the sea-breeze front propagation mean speed by about 0.32 m s-1 when compared with the situation of no city. After its arrival in the urban region, the sea-breeze front stalls over the centre of the city for about 2 h. Subsequently, the sea breeze progresses beyond the city when the heat island dissipates. Thereafter, the sea breeze propagates beyond the urban area at a decelerated rate compared to a simulation without an UHI.
Journal of Applied Meteorology, Jun 1, 2003
... Louis surface enhance boundary layer convection. Thielen et al. ... In fact, the 2D modeling ... more ... Louis surface enhance boundary layer convection. Thielen et al. ... In fact, the 2D modeling results of Thielen et al. (2000) indicate that sensible heat flux variations, due to the urban surface, provide the largest impact upon convection. ...
Agu Fall Meeting Abstracts, Dec 1, 2001
The land-use and land cover (LULC) history of the Baltimore-Washington region has been intensivel... more The land-use and land cover (LULC) history of the Baltimore-Washington region has been intensively studied through a variety of environmental research collaborations and regional partnerships. One such partnership, the Baltimore-Washington Regional Collaboratory, involved multiple Federal and local agencies cooperating on a 200-year urban growth study in the Chesapeake region. Information from this study on pre-1900 and current LULC conditions for the Baltimore-Washington DC area was integrated with data from other sources to construct different lower boundary conditions for a series of simulations using the Colorado State University (CSU) Regional Atmospheric Modeling System (RAMS). We use the RAMS simulations to diagnose the extent and nature of the effect of urban anomalies in surface heat, moisture, and momentum on mid-summer local and regional climate. The experimental design adopted for this study takes advantage of the grid-nesting capability of RAMS. A fine grid with 1km horizontal resolution was nested into a coarser 5 km grid, which extends from southern Pennsylvania, Maryland, to parts of Virginia, and West Virginia. Two sets of month-long simulations for July 2000 were conducted with RAMS running in parallel on a 26-processor cluster of computers at the Cooperative Institute for Research in the Atmosphere (CIRA), CSU. In the first set of simulations, we initially used satellite-derived current land cover data as the lower boundary condition in a 31-day RAMS run. We then replaced this data with the pre-1900 land cover data for the same region and ran a similar RAMS simulation. Identical observed meteorology was retained for the lateral boundary conditions in both cases. The model results for the initial run were validated with July 2000 surface climate data and flux measurements of sensible and latent heat from sites located within the fine grid model domain. Additional simulations were conducted to compare RAMS model performance using prescribed land surface conditions with results from a physically based scheme for urban energy budget coupled to RAMS. The urban surface scheme used here is the Town Energy Budget (TEB) model recently developed at the Center for Meteorological Research (CNRM), France. The TEB model allows for a refinement of model computed radiative budgets, heat and momentum based on a generalization of the classic canyon approach. Results from both sets of simulations, and the implications, for surface climate, of the driving human-induced land cover transformations are discussed.
Journal of Geophysical Research: Atmospheres, 2014
ABSTRACT
Bulletin of the American Meteorological Society, Jun 1, 2003
Bulletin of the American Meteorological Society
Data from a 22-year sample of Vortex Data Messages (VDMs) reveal that immature tropical cyclones ... more Data from a 22-year sample of Vortex Data Messages (VDMs) reveal that immature tropical cyclones (TCs) possess a wide variety of vortex structures at the time of initial eye formation. Such structures may be categorized into three groups according to the relation between the initial eye radius and the radius of maximum winds (RMW, defined as the time-trended lower bound of the radius of the flight-level maximum wind). In the first group, the immature TC structure closely resembles the canonical structure of more mature TCs, wherein the RMW is of a similar radial scale as the initial eye radius. In the second group, the RMW is more than twice the initial eye radius. In the final, smaller group, the RMW is found to be less than the initial eye radius (a situation that should not happen according to conventional understanding). These results highlight the fact that structure of immature TCs is not well understood. Since the majority of rapid intensification (RI)1 events commence when T...
Weather and Forecasting, 2015
2015: Evaluating environmental impacts on tropical cyclone rapid intensification AMERICAN METEORO... more 2015: Evaluating environmental impacts on tropical cyclone rapid intensification AMERICAN METEOROLOGICAL SOCIETY predictability utilizing statistical models. Wea. Forecasting.
Weather and Forecasting, 2015
ABSTRACT
Meteorologische Zeitschrift, 2004
... English translations of twenty-one of Ertel's papers on geophysical fluid dynamics WAYNE... more ... English translations of twenty-one of Ertel's papers on geophysical fluid dynamics WAYNE SCHUBERT ∗1, EBERHARD RUPRECHT 2, ROLF HERTENSTEIN 1, ROSANA NIETO FERREIRA 3, RICHARD TAFT 1, CHRISTOPHER ROZOFF 1, PAUL CIESIELSKI 1 and HUNG-...
In order to increase our fundamental understanding of rapid intensity change in tropical cyclones... more In order to increase our fundamental understanding of rapid intensity change in tropical cyclones (TCs), the evolving kinematic and thermodynamic conditions in TC eyewall replacement cycles and attendant moats are examined in this study. With the assistance of theory, observations, and cloud-resolving numerical simulations, the response of convection to typical environments outside of intense TC cores is addressed. In our analysis of the environmentally-dependent behaviors of deep, convective clouds, we consider new hypotheses and insights in rainband dynamics and concentric eyewall formation. Re-visiting basic stirring criteria for two-dimensional flows, we derive simple rules-of-thumb for the existence of deep, moist convection in environments of intense horizontal strain. These results are compared with numerical integrations of vorticity in a nondivergent barotropic model. The kinematic and thermodynamic environments during eyewall replacement cycles are documented through obser...
Weather and Forecasting, 2011
ABSTRACT
Quarterly Journal of the Royal Meteorological Society, 2008
The intensification of tropical cyclones is often interrupted by an eyewall replacement cycle, a ... more The intensification of tropical cyclones is often interrupted by an eyewall replacement cycle, a process in which an outer eyewall forms, contracts, and replaces an inner eyewall. The radial distributions of inertial stability and diabatic heating change during such events, impacting the transverse circulation. To examine the effects of such changes, an analytical solution of the transverse circulation equation associated with a balanced vortex model is derived using a parameterization that distinguishes five radial regions subdividing the domain by each region's values of inertial stability and diabatic heating. These regions define the eye, inner eyewall, moat, outer eyewall, and far-field. In mature concentric eyewall situations, the solutions do not support the hypothesis that the inner eyewall collapses as a direct result of subsidence from the outer eyewall. However, the results suggest subsidence and warming temperatures in the moat are governed by enhanced inertial stability associated with a strengthening outer eyewall. The model solutions also illustrate how the diabatic heating in the inner eyewall, imbedded in a region of high inertial stability, induces larger temperature tendencies than the diabatic heating in the outer eyewall, which borders the far-field region of low inertial stability. Thus, as the inner eyewall dies, the storm temporarily loses its ability to produce an intense, localized warm region. This ability is restored during the contraction and intensification of the outer eyewall. These results provide a partial dynamical explanation of how an eyewall replacement cycle can act as a temporary brake on tropical cyclone intensification.
Quarterly Journal of the Royal Meteorological Society, 2007
Two hurricane eye features that have yet to be adequately explained are the clear-air moat that f... more Two hurricane eye features that have yet to be adequately explained are the clear-air moat that forms at the outer edge of the eye and the hub cloud that forms near the circulation centre. To investigate whether these features can be explained by the spatial distribution of the subsidence field, we have derived an analytical solution of the Sawyer-Eliassen transverse circulation equation for a three-region approximation with an unforced central eye region of intermediate or high inertial stability, a diabatically-forced eyewall region of high inertial stability, and an unforced far-field of low inertial stability. This analytical solution isolates the conditions under which the subsidence is concentrated near the edge of the eye. The crucial parameter is the dimensionless dynamical radius of the eye, defined as the physical radius of the eye divided by the characteristic Rossby length in the eye. When this dimensionless dynamical radius is less than 0.6, there is less than 10% horizontal variation in the subsidence rate across the eye; when it is greater than 1.8, the subsidence rate at the edge of the eye is more than twice as strong as at the centre of the eye. When subsidence is concentrated at the edge of the eye, the largest temperature anomalies occur near there rather than at the vortex centre. This warm-ring structure, as opposed to a warm-core structure, is often observed in the lower troposphere of intense hurricanes.
Monthly Weather Review, 2012
Flight-level aircraft data are used to examine inner-core thermodynamic changes during eyewall re... more Flight-level aircraft data are used to examine inner-core thermodynamic changes during eyewall replacement cycles (ERCs) and the role of the relict inner eyewall circulation on the evolution of a hurricane during and following an ERC. Near the end of an ERC, the eye comprises two thermodynamically and kinematically distinct air masses separated by a relict wind maximum, inside of which high inertial stability restricts radial motion creating a ''containment vessel'' that confines the old-eye air mass. Restricted radial flow aloft also reduces subsidence within this confined region. Subsidence-induced warming is thus focused along the outer periphery of the developing post-ERC eye, which leads to a flattening of the pressure profile within the eye and a steepening of the gradient at the eyewall. This then causes a local intensification of the winds in the eyewall. The cessation of active convection and subsidence near the storm center, which has been occurring over the course of the ERC, leads to an increase in minimum pressure. The increase in minimum pressure concurrent with the increase of winds in the developing eyewall can create a highly anomalous pressure-wind relationship. When the relict inner eyewall circulation dissipates, the air masses are free to mix and subsidence can resume more uniformly over the entire eye.
Monthly Weather Review, 2011
A flight-level aircraft dataset consisting of 79 Atlantic basin hurricanes from 1977 to 2007 was ... more A flight-level aircraft dataset consisting of 79 Atlantic basin hurricanes from 1977 to 2007 was used to develop an unprecedented climatology of inner-core intensity and structure changes associated with eyewall replacement cycles (ERCs). During an ERC, the inner-core structure was found to undergo dramatic changes that result in an intensity oscillation and rapid broadening of the wind field. Concentrated temporal sampling by reconnaissance aircraft in 14 of the 79 hurricanes captured virtually the entire evolution of 24 ERC events. The analysis of this large dataset extends the phenomenological paradigm of ERCs described in previous observational case studies by identifying and exploring three distinct phases of ERCs: intensification, weakening, and reintensification. In general, hurricanes intensify, sometimes rapidly, when outer wind maxima are first encountered by aircraft. The mean locations of the inner and outer wind maximum at the start of an ERC are 35 and 106 km from storm center, respectively. The intensification rate of the inner wind maximum begins to slow and the storm ultimately weakens as the inner-core structure begins to organize into concentric rings. On average, the inner wind maximum weakens 10 m s 21 before the outer wind maximum surpasses the inner wind maximum as it continues to intensify. This reintensification can be quite dramatic and often brings the storm to its maximum lifetime intensity. The entire ERC lasts 36 h on average.
Boundary Layer Meteorology, 2007
The Town Energy Budget (TEB) model, a detailed urban parameterisation using a generalised canyon ... more The Town Energy Budget (TEB) model, a detailed urban parameterisation using a generalised canyon geometry, coupled with the Regional Atmospheric Modelling System (RAMS) is used to simulate the wintertime local circulation in the megacity environment of the metropolitan area of Sao Paulo (MASP) in Brazil. Model simulations are performed using actual topography and land-use fields. Comparison with a simple urban parameterisation based on the LEAF-2 scheme is also shown. Validation is based on comparison between model simulations and observations. Sensitivity tests with TEB reveal an important interaction between the sea breeze and the MASP heat island circulation. Even though topography is known to play an important role in the MASP region’s weather, in these tests the simulations were performed without topography in order to unambiguously identify the interaction between the two local circulations. The urban heat island (UHI) forms a strong convergence zone in the centre of the city and thereby accelerates the sea-breeze front toward the centre of the city. The presence of the urban region increases the sea-breeze front propagation mean speed by about 0.32 m s-1 when compared with the situation of no city. After its arrival in the urban region, the sea-breeze front stalls over the centre of the city for about 2 h. Subsequently, the sea breeze progresses beyond the city when the heat island dissipates. Thereafter, the sea breeze propagates beyond the urban area at a decelerated rate compared to a simulation without an UHI.
Journal of Applied Meteorology, Jun 1, 2003
... Louis surface enhance boundary layer convection. Thielen et al. ... In fact, the 2D modeling ... more ... Louis surface enhance boundary layer convection. Thielen et al. ... In fact, the 2D modeling results of Thielen et al. (2000) indicate that sensible heat flux variations, due to the urban surface, provide the largest impact upon convection. ...
Agu Fall Meeting Abstracts, Dec 1, 2001
The land-use and land cover (LULC) history of the Baltimore-Washington region has been intensivel... more The land-use and land cover (LULC) history of the Baltimore-Washington region has been intensively studied through a variety of environmental research collaborations and regional partnerships. One such partnership, the Baltimore-Washington Regional Collaboratory, involved multiple Federal and local agencies cooperating on a 200-year urban growth study in the Chesapeake region. Information from this study on pre-1900 and current LULC conditions for the Baltimore-Washington DC area was integrated with data from other sources to construct different lower boundary conditions for a series of simulations using the Colorado State University (CSU) Regional Atmospheric Modeling System (RAMS). We use the RAMS simulations to diagnose the extent and nature of the effect of urban anomalies in surface heat, moisture, and momentum on mid-summer local and regional climate. The experimental design adopted for this study takes advantage of the grid-nesting capability of RAMS. A fine grid with 1km horizontal resolution was nested into a coarser 5 km grid, which extends from southern Pennsylvania, Maryland, to parts of Virginia, and West Virginia. Two sets of month-long simulations for July 2000 were conducted with RAMS running in parallel on a 26-processor cluster of computers at the Cooperative Institute for Research in the Atmosphere (CIRA), CSU. In the first set of simulations, we initially used satellite-derived current land cover data as the lower boundary condition in a 31-day RAMS run. We then replaced this data with the pre-1900 land cover data for the same region and ran a similar RAMS simulation. Identical observed meteorology was retained for the lateral boundary conditions in both cases. The model results for the initial run were validated with July 2000 surface climate data and flux measurements of sensible and latent heat from sites located within the fine grid model domain. Additional simulations were conducted to compare RAMS model performance using prescribed land surface conditions with results from a physically based scheme for urban energy budget coupled to RAMS. The urban surface scheme used here is the Town Energy Budget (TEB) model recently developed at the Center for Meteorological Research (CNRM), France. The TEB model allows for a refinement of model computed radiative budgets, heat and momentum based on a generalization of the classic canyon approach. Results from both sets of simulations, and the implications, for surface climate, of the driving human-induced land cover transformations are discussed.
Journal of Geophysical Research: Atmospheres, 2014
ABSTRACT
Bulletin of the American Meteorological Society, Jun 1, 2003
Bulletin of the American Meteorological Society
Data from a 22-year sample of Vortex Data Messages (VDMs) reveal that immature tropical cyclones ... more Data from a 22-year sample of Vortex Data Messages (VDMs) reveal that immature tropical cyclones (TCs) possess a wide variety of vortex structures at the time of initial eye formation. Such structures may be categorized into three groups according to the relation between the initial eye radius and the radius of maximum winds (RMW, defined as the time-trended lower bound of the radius of the flight-level maximum wind). In the first group, the immature TC structure closely resembles the canonical structure of more mature TCs, wherein the RMW is of a similar radial scale as the initial eye radius. In the second group, the RMW is more than twice the initial eye radius. In the final, smaller group, the RMW is found to be less than the initial eye radius (a situation that should not happen according to conventional understanding). These results highlight the fact that structure of immature TCs is not well understood. Since the majority of rapid intensification (RI)1 events commence when T...
Weather and Forecasting, 2015
2015: Evaluating environmental impacts on tropical cyclone rapid intensification AMERICAN METEORO... more 2015: Evaluating environmental impacts on tropical cyclone rapid intensification AMERICAN METEOROLOGICAL SOCIETY predictability utilizing statistical models. Wea. Forecasting.
Weather and Forecasting, 2015
ABSTRACT
Meteorologische Zeitschrift, 2004
... English translations of twenty-one of Ertel's papers on geophysical fluid dynamics WAYNE... more ... English translations of twenty-one of Ertel's papers on geophysical fluid dynamics WAYNE SCHUBERT ∗1, EBERHARD RUPRECHT 2, ROLF HERTENSTEIN 1, ROSANA NIETO FERREIRA 3, RICHARD TAFT 1, CHRISTOPHER ROZOFF 1, PAUL CIESIELSKI 1 and HUNG-...
In order to increase our fundamental understanding of rapid intensity change in tropical cyclones... more In order to increase our fundamental understanding of rapid intensity change in tropical cyclones (TCs), the evolving kinematic and thermodynamic conditions in TC eyewall replacement cycles and attendant moats are examined in this study. With the assistance of theory, observations, and cloud-resolving numerical simulations, the response of convection to typical environments outside of intense TC cores is addressed. In our analysis of the environmentally-dependent behaviors of deep, convective clouds, we consider new hypotheses and insights in rainband dynamics and concentric eyewall formation. Re-visiting basic stirring criteria for two-dimensional flows, we derive simple rules-of-thumb for the existence of deep, moist convection in environments of intense horizontal strain. These results are compared with numerical integrations of vorticity in a nondivergent barotropic model. The kinematic and thermodynamic environments during eyewall replacement cycles are documented through obser...
Weather and Forecasting, 2011
ABSTRACT
Quarterly Journal of the Royal Meteorological Society, 2008
The intensification of tropical cyclones is often interrupted by an eyewall replacement cycle, a ... more The intensification of tropical cyclones is often interrupted by an eyewall replacement cycle, a process in which an outer eyewall forms, contracts, and replaces an inner eyewall. The radial distributions of inertial stability and diabatic heating change during such events, impacting the transverse circulation. To examine the effects of such changes, an analytical solution of the transverse circulation equation associated with a balanced vortex model is derived using a parameterization that distinguishes five radial regions subdividing the domain by each region's values of inertial stability and diabatic heating. These regions define the eye, inner eyewall, moat, outer eyewall, and far-field. In mature concentric eyewall situations, the solutions do not support the hypothesis that the inner eyewall collapses as a direct result of subsidence from the outer eyewall. However, the results suggest subsidence and warming temperatures in the moat are governed by enhanced inertial stability associated with a strengthening outer eyewall. The model solutions also illustrate how the diabatic heating in the inner eyewall, imbedded in a region of high inertial stability, induces larger temperature tendencies than the diabatic heating in the outer eyewall, which borders the far-field region of low inertial stability. Thus, as the inner eyewall dies, the storm temporarily loses its ability to produce an intense, localized warm region. This ability is restored during the contraction and intensification of the outer eyewall. These results provide a partial dynamical explanation of how an eyewall replacement cycle can act as a temporary brake on tropical cyclone intensification.
Quarterly Journal of the Royal Meteorological Society, 2007
Two hurricane eye features that have yet to be adequately explained are the clear-air moat that f... more Two hurricane eye features that have yet to be adequately explained are the clear-air moat that forms at the outer edge of the eye and the hub cloud that forms near the circulation centre. To investigate whether these features can be explained by the spatial distribution of the subsidence field, we have derived an analytical solution of the Sawyer-Eliassen transverse circulation equation for a three-region approximation with an unforced central eye region of intermediate or high inertial stability, a diabatically-forced eyewall region of high inertial stability, and an unforced far-field of low inertial stability. This analytical solution isolates the conditions under which the subsidence is concentrated near the edge of the eye. The crucial parameter is the dimensionless dynamical radius of the eye, defined as the physical radius of the eye divided by the characteristic Rossby length in the eye. When this dimensionless dynamical radius is less than 0.6, there is less than 10% horizontal variation in the subsidence rate across the eye; when it is greater than 1.8, the subsidence rate at the edge of the eye is more than twice as strong as at the centre of the eye. When subsidence is concentrated at the edge of the eye, the largest temperature anomalies occur near there rather than at the vortex centre. This warm-ring structure, as opposed to a warm-core structure, is often observed in the lower troposphere of intense hurricanes.
Monthly Weather Review, 2012
Flight-level aircraft data are used to examine inner-core thermodynamic changes during eyewall re... more Flight-level aircraft data are used to examine inner-core thermodynamic changes during eyewall replacement cycles (ERCs) and the role of the relict inner eyewall circulation on the evolution of a hurricane during and following an ERC. Near the end of an ERC, the eye comprises two thermodynamically and kinematically distinct air masses separated by a relict wind maximum, inside of which high inertial stability restricts radial motion creating a ''containment vessel'' that confines the old-eye air mass. Restricted radial flow aloft also reduces subsidence within this confined region. Subsidence-induced warming is thus focused along the outer periphery of the developing post-ERC eye, which leads to a flattening of the pressure profile within the eye and a steepening of the gradient at the eyewall. This then causes a local intensification of the winds in the eyewall. The cessation of active convection and subsidence near the storm center, which has been occurring over the course of the ERC, leads to an increase in minimum pressure. The increase in minimum pressure concurrent with the increase of winds in the developing eyewall can create a highly anomalous pressure-wind relationship. When the relict inner eyewall circulation dissipates, the air masses are free to mix and subsidence can resume more uniformly over the entire eye.
Monthly Weather Review, 2011
A flight-level aircraft dataset consisting of 79 Atlantic basin hurricanes from 1977 to 2007 was ... more A flight-level aircraft dataset consisting of 79 Atlantic basin hurricanes from 1977 to 2007 was used to develop an unprecedented climatology of inner-core intensity and structure changes associated with eyewall replacement cycles (ERCs). During an ERC, the inner-core structure was found to undergo dramatic changes that result in an intensity oscillation and rapid broadening of the wind field. Concentrated temporal sampling by reconnaissance aircraft in 14 of the 79 hurricanes captured virtually the entire evolution of 24 ERC events. The analysis of this large dataset extends the phenomenological paradigm of ERCs described in previous observational case studies by identifying and exploring three distinct phases of ERCs: intensification, weakening, and reintensification. In general, hurricanes intensify, sometimes rapidly, when outer wind maxima are first encountered by aircraft. The mean locations of the inner and outer wind maximum at the start of an ERC are 35 and 106 km from storm center, respectively. The intensification rate of the inner wind maximum begins to slow and the storm ultimately weakens as the inner-core structure begins to organize into concentric rings. On average, the inner wind maximum weakens 10 m s 21 before the outer wind maximum surpasses the inner wind maximum as it continues to intensify. This reintensification can be quite dramatic and often brings the storm to its maximum lifetime intensity. The entire ERC lasts 36 h on average.