scholarly journals Observation of the Tropical Cyclone Diurnal Cycle Using Hyperspectral Infrared Satellite Sounding Retrievals

2021 ◽  
Author(s):  
Erika L. Duran ◽  
Emily B. Berndt ◽  
Patrick Duran
Keyword(s):  
Tropical Cyclone ◽  
Diurnal Cycle ◽  
Inner Core ◽  
Deep Layer ◽  
Deep Convection ◽  
Satellite System ◽  
Radiative Heating ◽  
Lapse Rate ◽  
Vertical Profiles ◽  
Microwave Sounding

AbstractHyperspectral infrared satellite sounding retrievals are used to examine thermodynamic changes in the tropical cyclone (TC) environment associated with the diurnal cycle of radiation. Vertical profiles of temperature and moisture are retrieved from the Suomi National Polar–orbiting Partnership (S–NPP) satellite system, National Oceanic and Atmospheric Administration (NOAA)–20, and the Meteorological Operational (MetOp) A/B satellite system, leveraging both infrared and microwave sounding technologies. Vertical profiles are binned radially based on distance from the storm center and composited at 4–hr intervals to reveal the evolution of the diurnal cycle. For the three cases examined – Hurricane Dorian (2019), Hurricane Florence (2018) and Hurricane Irma (2017) – a marked diurnal signal is evident that extends through a deep layer of the troposphere. Statistically significant differences at the 95% level are observed in temperature, moisture, and lapse rate profiles, indicating a moistening and destabilization of the mid to upper troposphere that is more pronounced near the inner core of the TC at night. Observations support a favorable environment for the formation of deep convection caused by diurnal differences in radiative heating tendencies, which could partially explain why new diurnal pulses tend to form around sunset. These findings demonstrate that the diurnal cycle of radiation affects TC thermodynamics through a deep layer of the troposphere, and suggest that hyperspectral infrared satellite sounding retrievals are valuable assets in detecting thermodynamic variations in TCs.

scholarly journals Tropical Cyclone Diurnal Cycle as Observed by TRMM

2016 ◽  
Vol 144 (8) ◽  
pp. 2793-2808 ◽  
Author(s):  
Kenneth D. Leppert ◽  
Daniel J. Cecil
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Diurnal Cycle ◽  
Inner Core ◽  
Deep Layer ◽  
Tropical Rainfall Measuring Mission ◽  
Local Standard ◽  
Intensity Changes ◽  
Microwave Imager ◽  
Trmm Microwave Imager

Abstract Previous work has indicated a clear, consistent diurnal cycle in rainfall and cold cloudiness coverage around tropical cyclones. This cycle may have important implications for structure and intensity changes of these storms and the forecasting of such changes. The goal of this paper is to use passive and active microwave measurements from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and Precipitation Radar (PR), respectively, to better understand the tropical cyclone diurnal cycle throughout a deep layer of a tropical cyclone’s clouds. The composite coverage by PR reflectivity ≥20 dBZ at various heights as a function of local standard time (LST) and radius suggests the presence of a diurnal signal for radii <500 km through a deep layer (2–10-km height) of the troposphere using 1998–2011 Atlantic tropical cyclones of at least tropical storm strength. The area covered by reflectivity ≥20 dBZ at radii 100–500 km peaks in the morning (0130–1030 LST) and reaches a minimum 1030–1930 LST. Radii between 300 and 500 km tend to reach a minimum in coverage closer to 1200 LST before reaching another peak at 2100 LST. The inner core (0–100 km) appears to be associated with a single-peaked diurnal cycle only at upper levels (8–10 km) with a maximum at 2230–0430 LST. The TMI rainfall composites suggest a clear diurnal cycle at all radii between 200 and 1000 km with peak rainfall coverage and rain rate occurring in the morning (0130–0730 LST).

scholarly journals A High-Resolution Simulation of Asymmetries in Severe Southern Hemisphere Tropical Cyclone Larry (2006)

2009 ◽  
Vol 137 (12) ◽  
pp. 4171-4187 ◽  
Author(s):  
Hamish A. Ramsay ◽  
Lance M. Leslie ◽  
Jeffrey D. Kepert
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Southern Hemisphere ◽  
Inner Core ◽  
Mesoscale Model ◽  
Deep Convection ◽  
Vertical Motion ◽  
Vertical Shear ◽  
Low Level ◽  
Frictional Convergence

Abstract Advances in observations, theory, and modeling have revealed that inner-core asymmetries are a common feature of tropical cyclones (TCs). In this study, the inner-core asymmetries of a severe Southern Hemisphere tropical cyclone, TC Larry (2006), are investigated using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) and the Kepert–Wang boundary layer model. The MM5-simulated TC exhibited significant asymmetries in the inner-core region, including rainfall distribution, surface convergence, and low-level vertical motion. The near-core environment was characterized by very low environmental vertical shear and consequently the TC vortex had almost no vertical tilt. It was found that, prior to landfall, the rainfall asymmetry was very pronounced with precipitation maxima consistently to the right of the westward direction of motion. Persistent maxima in low-level convergence and vertical motion formed ahead of the translating TC, resulting in deep convection and associated hydrometeor maxima at about 500 hPa. The asymmetry in frictional convergence was mainly due to the storm motion at the eyewall, but was dominated by the proximity to land at larger radii. The displacement of about 30°–120° of azimuth between the surface and midlevel hydrometeor maxima is explained by the rapid cyclonic advection of hydrometeors by the tangential winds in the TC core. These results for TC Larry support earlier studies that show that frictional convergence in the boundary layer can play a significant role in determining the asymmetrical structures, particularly when the environmental vertical shear is weak or absent.

scholarly journals Passive Microwave Quantification of Tropical Cyclone Inner-Core Cloud Populations Relative to Subsequent Intensity Change

2016 ◽  
Vol 144 (11) ◽  
pp. 4461-4482 ◽  
Author(s):  
Daniel S. Harnos ◽  
Stephen W. Nesbitt
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Statistical Significance ◽  
Deep Convection ◽  
Detection Algorithm ◽  
Passive Microwave ◽  
Intensity Change ◽  
Atmospheric Column ◽  
Full Intensity ◽  
Relative Prevalence

Abstract Characteristics of over 15 000 tropical cyclone (TC) inner cores are evaluated coincidentally using 37- and 85-GHz passive microwave data to quantify the relative prevalence of cold clouds (i.e., deep convection and stratiform clouds) versus predominantly warm clouds (i.e., shallow cumuli and cumulus congestus). Results indicate greater presence of combined liquid and frozen hydrometeors associated with cold clouds within the atmospheric column for TCs undergoing subsequent rapid intensification (RI) or intensification. RI episodes compared to the full intensity change distribution exhibit approximately an order of magnitude increase for inner-core cold cloud frequency relative to warm cloud presence. Incorporation of an objective ring detection algorithm shows the robust presence of rings associated with hydrometeors for 85-GHz polarization corrected temperatures () and 37-GHz vertically polarized brightness temperatures () for differentiating RI with significance levels ≥99.99%, while 37-GHz false color rings of a combined cyan and pink appearance surrounding a region that is not cyan or pink lack statistical significance for discriminating RI against lesser intensification. Rings of depressed and enhanced tied to RI suggest the combined presence of liquid and frozen hydrometeors within the atmospheric column, indicative of cold clouds. The rings also exhibit preferences for those with collocated more widespread ice scattering signatures to be more commonly associated with RI and general intensification.

Diurnal differences in tropical maritime anvil cloud evolution

2021 ◽  
pp. 1-66
Author(s):  
Adam B. Sokol ◽  
Casey J. Wall ◽  
Dennis L. Hartmann ◽  
Peter N. Blossey
Keyword(s):  
Diurnal Cycle ◽  
Deep Convection ◽  
Radiative Heating ◽  
Cloud Base ◽  
Diurnal Difference ◽  
Size Number ◽  
Cloud Resolving Model ◽  
Ice Crystal Size ◽  
Environmental Air ◽  
Cloud Evolution

Abstract Satellite observations of tropical maritime convection indicate an afternoon maximum in anvil cloud fraction that cannot be explained by the diurnal cycle of deep convection peaking at night. We use idealized cloud-resolving model simulations of single anvil cloud evolution pathways, initialized at different times of the day, to show that tropical anvil clouds formed during the day are more widespread and longer lasting than those formed at night. This diurnal difference is caused by shortwave radiative heating, which lofts and spreads anvil clouds via a mesoscale circulation that is largely absent at night, when a different, longwave-driven circulation dominates. The nighttime circulation entrains dry environmental air that erodes cloud top and shortens anvil lifetime. Increased ice nucleation in more turbulent nighttime conditions supported by the longwave cloud top cooling and cloud base heating dipole cannot overcompensate for the effect of diurnal shortwave radiative heating. Radiative-convective equilibrium simulations with a realistic diurnal cycle of insolation confirm the crucial role of shortwave heating in lofting and sustaining anvil clouds. The shortwave-driven mesoscale ascent leads to daytime anvils with larger ice crystal size, number concentration, and water content at cloud top than their nighttime counterparts.

Diurnal Cycles of Synthetic Microwave Sounding Lower-Stratospheric Temperatures from Radio Occultation Observations, Reanalysis, and Model Simulations

2021 ◽  
Author(s):  
Aodhan J Sweeney ◽  
Qiang Fu
Keyword(s):  
Diurnal Cycle ◽  
Radio Occultation ◽  
Lower Stratosphere ◽  
Deep Convection ◽  
Winter Season ◽  
Boreal Winter ◽  
Diurnal Cycles ◽  
Stratospheric Temperature ◽  
Diurnal Range ◽  
Microwave Sounding

AbstractAn observationally-based global climatology of the temperature diurnal cycle in the lower stratosphere is derived from eleven different satellites with Global Positioning System-Radio Occultation (GPS-RO) measurements from 2006-2020. Methods used in our analysis allow for accurate characterization of global stratospheric temperature diurnal cycles, even in the high latitudes where the diurnal signal is small but longer timescale variability is large. A climatology of the synthetic Microwave Sounding Unit (MSU) and Advanced MSU (AMSU) Temperature in the Lower Stratosphere (TLS) is presented to assess the accuracy of diurnal cycle climatologies for the MSU and AMSU TLS observations, which have traditionally been generated by model data. The TLS diurnal temperature ranges are typically less than 0.4 K in all latitude bands and seasons investigated. It is shown that the diurnal range (maximum minus minimum temperature) of TLS is largest over southern hemisphere tropical land in the boreal winter season, indicating the important role of deep convection. The range, phase, and seasonality of the TLS diurnal cycle are generally well captured by the WACCM6 simulation and ERA5 reanalysis. We also present an observationally-based diurnal cycle climatology of temperature profiles from 300-10 hPa for various latitude bands and seasons and compare the ERA5 reanalysis with the observations.

scholarly journals The Roles of Asymmetric Inflow Forcing Induced by Outer Rainbands in Tropical Cyclone Secondary Eyewall Formation

2013 ◽  
Vol 70 (3) ◽  
pp. 953-974 ◽  
Author(s):  
Xin Qiu ◽  
Zhe-Min Tan
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Early Phase ◽  
Inner Core ◽  
Deep Convection ◽  
Leading Edge ◽  
Three Dimensions ◽  
Secondary Eyewall Formation ◽  
Layer Flow ◽  
The Impact

Abstract This study analyzes the secondary eyewall formation (SEF) process in an idealized cloud-resolving simulation of a tropical cyclone. In particular, the unbalanced boundary layer response to asymmetric inflow forcing induced by outer rainbands (ORBs) is examined in order to understand the mechanisms driving the sustained convection outside the primary eyewall during the early phase of SEF. The enhancement of convection in the SEF region follows the formation and inward contraction of an ORB. The azimuthal distribution of the enhanced convection is highly asymmetric but regular, generally along a half circle starting from the downwind portion of the ORB. It turns out that the descending radial inflow in the middle and downwind portions of the ORB initiates/maintains a strong inflow in the boundary layer. The latter is able to penetrate into the inner-core region, sharpens the gradient of radial velocity, and reinforces convergence. Consequently, warm and moist air is continuously lifted up at the leading edge of the strong inflow to support deep convection. Moreover, the inflow from the ORB creates strong supergradient winds that are ejected outward downwind, thereby enhancing convergence and convection on the other side of the storm. The results provide new insight into the key processes responsible for convection enhancement during the early phase of SEF in three dimensions and suggest the limitations of axisymmetric studies. There are also implications regarding the impact of the asymmetric boundary layer flow under a translating storm on SEF.

scholarly journals Estimating Tropical Cyclone Integrated Kinetic Energy with the CYGNSS Satellite Constellation

2017 ◽  
Vol 56 (1) ◽  
pp. 235-245 ◽  
Author(s):  
Mary Morris ◽  
Christopher S. Ruf
Keyword(s):  
Tropical Cyclone ◽  
Kinetic Energy ◽  
Tropical Cyclones ◽  
Measurement Errors ◽  
Inner Core ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Satellite System ◽  
Insurance Companies ◽  
High Temporal Resolution

AbstractThe Cyclone Global Navigation Satellite System (CYGNSS) constellation is designed to provide observations of surface wind speed in and near the inner core of tropical cyclones with high temporal resolution throughout the storm’s life cycle. A method is developed for estimating tropical cyclone integrated kinetic energy (IKE) using CYGNSS observations. IKE is calculated for each geographically based quadrant out to an estimate of the 34-kt (1 kt = 0.51 m s−1) wind radius. The CYGNSS-IKE estimator is tested and its performance is characterized using simulated CYGNSS observations with realistic measurement errors. CYGNSS-IKE performance improves for stronger, more organized storms and with increasing number of observations over the extent of the 34-kt radius. Known sampling information can be used for quality control. While CYGNSS-IKE is calculated for individual geographic quadrants, using a total-IKE—a sum over all quadrants—improves performance. CYGNSS-IKE should be of interest to operational and research meteorologists, insurance companies, and others interested in the destructive potential of tropical cyclones developing in data-sparse regions, which will now be covered by CYGNSS. The CYGNSS-IKE product will be available for the 2017 Atlantic Ocean hurricane season.

scholarly journals Role of Cumulus Congestus in Tropical Cyclone Formation in a High-Resolution Numerical Model Simulation

2014 ◽  
Vol 71 (5) ◽  
pp. 1681-1700 ◽  
Author(s):  
Zhuo Wang
Keyword(s):  
High Resolution ◽  
Tropical Cyclone ◽  
Deep Layer ◽  
Dominant Role ◽  
Rapid Development ◽  
Deep Convection ◽  
Cyclonic Circulation ◽  
Low Level ◽  
Cumulus Congestus

Abstract The role of cumulus congestus (shallow and congestus convection) in tropical cyclone (TC) formation is examined in a high-resolution simulation of Tropical Cyclone Fay (2008). It is found that cumulus congestus plays a dominant role in moistening the lower to middle troposphere and spinning up the near-surface circulation prior to genesis, while deep convection plays a key role in moistening the upper troposphere and intensifying the cyclonic circulation over a deep layer. The transition from the tropical wave stage to the TC stage is marked by a substantial increase in net condensation and potential vorticity generation by deep convection in the inner wave pouch region. This study suggests that TC formation can be regarded as a two-stage process. The first stage is a gradual process of moisture preconditioning and low-level spinup, in which cumulus congestus plays a dominant role. The second stage commences with the rapid development of deep convection in the inner pouch region after the air column is moistened sufficiently, whereupon the concentrated convective heating near the pouch center strengthens the transverse circulation and leads to the amplification of the cyclonic circulation over a deep layer. The rapid development of deep convection can be explained by the power-law increase of precipitation rate with column water vapor (CWV) above a critical value. The high CWV near the pouch center thus plays an important role in convective organization. It is also shown that cumulus congestus can effectively drive the low-level convergence and provides a direct and simple pathway for the development of the TC protovortex near the surface.

The Tropical Cyclone Diurnal Cycle of Mature Hurricanes

2014 ◽  
Vol 142 (10) ◽  
pp. 3900-3919 ◽  
Author(s):  
Jason P. Dunion ◽  
Christopher D. Thorncroft ◽  
Christopher S. Velden
Keyword(s):  
Tropical Cyclone ◽  
Diurnal Cycle ◽  
Structural Changes ◽  
Inner Core ◽  
Satellite Image ◽  
Intensity Change ◽  
Ongoing Research ◽  
Image Differencing ◽  
A New Technique ◽  
Cloud Tops

Abstract The diurnal cycle of tropical convection and the tropical cyclone (TC) cirrus canopy has been described extensively in previous studies. However, a complete understanding of the TC diurnal cycle remains elusive and is an area of ongoing research. This work describes a new technique that uses infrared satellite image differencing to examine the evolution of the TC diurnal cycle for all North Atlantic major hurricanes from 2001 to 2010. The imagery reveals cyclical pulses in the infrared cloud field that regularly propagate radially outward from the storm. These diurnal pulses begin forming in the storm’s inner core near the time of sunset each day and continue to move away from the storm overnight, reaching areas several hundreds of kilometers from the circulation center by the following afternoon. A marked warming of the cloud tops occurs behind this propagating feature and there can be pronounced structural changes to a storm as it moves away from the inner core. This suggests that the TC diurnal cycle may be an important element of TC dynamics and may have relevance to TC structure and intensity change. Evidence is also presented showing the existence of statistically significant diurnal signals in TC wind radii and objective Dvorak satellite-based intensity estimates for the 10-yr hurricane dataset that was examined. Findings indicate that TC diurnal pulses are a distinguishing characteristic of the TC diurnal cycle and the repeatability of TC diurnal pulsing in time and space suggests that it may be an unrealized, yet fundamental TC process.

scholarly journals Effects of Midlevel Dry Air on Development of the Axisymmetric Tropical Cyclone Secondary Circulation

2017 ◽  
Vol 74 (5) ◽  
pp. 1455-1470 ◽  
Author(s):  
Joshua J. Alland ◽  
Brian H. Tang ◽  
Kristen L. Corbosiero
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Deep Convection ◽  
Surface Fluxes ◽  
Secondary Circulation ◽  
Overturning Circulation ◽  
Dry Air ◽  
Turbulent Entrainment ◽  
Convective Motions ◽  
Lower Entropy

Abstract Idealized experiments conducted with an axisymmetric tropical cyclone (TC) model are used to assess the effects of midlevel dry air on the axisymmetric TC secondary circulation. Moist entropy diagnostics of convective parcels are used to determine how midlevel dry air affects the distribution and strength of convection. Analyzing upward and downward motions in the Eulerian radius–height coordinate system shows that the moistest simulation has stronger vertical motions and a wider overturning circulation compared to drier simulations. A Lagrangian entropy framework further analyzes convective motions by separating upward higher-entropy streams from downward lower-entropy streams. Results show that the driest simulation has a weaker mean overturning circulation with updrafts characterized by lower mean entropy compared to moister simulations. Turbulent entrainment of dry air into deep convection at midlevels is small, suggesting that the influence of midlevel dry air on convective strength and the structure of the secondary circulation are through modification of the inflow layer. Backward trajectories show low-entropy air subsiding into the subcloud layer from low to midlevels of the atmosphere between radii of 200 and 400 km. Surface fluxes increase the entropy of these parcels before they rise in convective updrafts, but the increased recovery time, combined with descending motion closer to the inner core, decreases the width of the TC secondary circulation in the driest simulation.

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