53 research outputs found
The genesis of Hurricane Nate and its interaction with a nearby environment of very dry air
The Supplement related to this article is available
online at https://doi.org/10.5194/acp-17-10349-2017-supplementThe article of record as published may be found at http://dx.doi.org/10.5194/acp-17-10349-2017The interaction of a tropical disturbance with its
environment is thought to play an important role in whether
a disturbance will develop or not. Most developing disturbances are somewhat protected from the intrusion of environmental dry air at mid-levels. For African easterly wave
(AEW) disturbances, the protective boundary is approximated by closed streamlines in the wave-relative frame, and
their interior is called the wave pouch. The dynamic and thermodynamic processes of spin-up occur inside the pouch.
In this study, we define the kinematic boundaries for a nonAEW disturbance in the Bay of Campeche that originated
along a sharp frontal boundary in a confluent region of low
pressure. We examine these boundaries during the genesis of
Hurricane Nate (2011) to show how a pouch boundary on
isobaric levels in the Lagrangian frame may allow for some
transport into the pouch along the frontal boundary while
still protecting the innermost development region. This result illustrates a generic property of weakly unsteady flows,
including the time-dependent critical layer of AEWs, that lateral exchange of air occurs along a segment of the boundary
formed by the instantaneous, closed translating streamlines.
Transport in the Lagrangian frame is simplest when measured with respect to the stable and unstable manifolds of
a hyperbolic trajectory, which are topologically invariant. In
this framework, an exact analysis of vorticity transport identifies the primary source as the advection of vorticity through
the entrainment and expulsion of bounded material regions
called lobes. We also show how these Lagrangian boundaries
impact the concentration of moisture, influence convection,
and contribute to the pouch vertical structure.NSFNASAAGS-1313948AGS-1439283AGS-0733380NNG11PK02
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Sub-seasonal variations in lower stratospheric water vapor
Observations of water vapor with high temporal and spatial resolution and good horizontal coverage just above the tropical tropopause have been scarce, but a preliminary version of such data has been developed using radiance measurements of the Microwave Limb Sounder. These data reveal distinct variations with periods in the ranges 10-25 days and 30-70 days, consistent with (respectively) slow Kelvin waves and the tropical intraseasonal oscillation
On the existence of the logarithmic surface layer in the inner-core of hurricanes
Q. J. R. Meteorol. Soc., 1394128
Extratropical Impacts on Atlantic Tropical Cyclone Activity
With warm sea surface temperature (SST) anomalies in the tropical Atlantic and cold SST anomalies in the east Pacific, the unusually quiet hurricane season in 2013 was a surprise to the hurricane community. The authors' analyses suggest that the substantially suppressed Atlantic tropical cyclone (TC) activity in August 2013 can be attributed to frequent breaking of midlatitude Rossby waves, which led to the equatorward intrusion of cold and dry extratropical air. The resultant mid- to upper-tropospheric dryness and strong vertical wind shear hindered TC development. Using the empirical orthogonal function analysis, the active Rossby wave breaking in August 2013 was found to be associated with a recurrent mode of the midlatitude jet stream over the North Atlantic, which represents the variability of the intensity and zonal extent of the jet. This mode is significantly correlated with Atlantic hurricane frequency. The correlation coefficient is comparable to the correlation of Atlantic hurricane frequency with the main development region (MDR) relative SST and higher than that with the Niño-3.4 index. This study highlights the extratropical impacts on Atlantic TC activity, which may have important implications for the seasonal predictability of Atlantic TCs
Application of the Marsupial Paradigm to Tropical Cyclone Formation from Northwestward Propagating Disturbances
Mon. Wea. Rev., 140 66-76The article of record as published may be located at http://dx.doi.org/10.1175/2011MWR3604.
Annual Variation of Deseasonalized Mean Flow Acceleration in the Equatorial Lower Stratosphere
Decadal Variability and Temperature Trends in the Middle Atmosphere From Historical Rocketsonde Data
Observational studies were performed using historical rocketsonde data to investigate long-term temperature trends, solar-cycle variations, and interactions between tropical and extratropical latitudes in the middle atmosphere. Evidence from tropical, subtropical, and midlatitude North American rocketsonde stations indicated a consistent downward trend over 25 years, with a solar cycle component superposed. The trend is about -1.4 to -2.0 K per decade and the amplitude of the decadal oscillation is about 1.1 K. Prior to trend derivation it was necessary for us to correct temperatures for aerodynamic heating in the early years. The empirically derived correction profile agrees well with a theoretical profile of Krumins and Lyons. A study was also performed of the correlation between equatorial winds and north polar temperatures in winter, showing that the entire stratospheric wind profile near the equator -- including the quasi-biennial oscillation (QBO) and stratopause semiannual oscillation (SAO) -- is important to the extratropical flow, not merely the QBO component as previously thought. A strong correlation was discovered between winter polar temperatures and equatorial winds in the upper stratosphere during the preceding September, suggesting a role for the second cycle of the SAO
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