Posted in Articles, Mesoscale Eddies, VOCALS

Using Lagrangian Coherent Structures with atmospheric data

 

I recently read this article on the use of Lagrangian coherent structures to inform on turbulence in the atmosphere near an airport.

Accurate extraction of Lagrangian coherent structures over finite domains with application to flight data analysis over Hong Kong International Airport.

W Tang and PW Chan.

Traditional approaches in the extraction of Lagrangian coherent structures (LCS) using finite-time Lyapunov exponents (FTLE) stop trajectories at the domain boundaries when data are only available in a limited region. This turns the domain boundaries into attractors and deteriorates the quality of the extraction. Direct application of this approach to practical problems is troublesome as spurious ridges appear and true ridges are suppressed, causing errors in the evaluation of a nonlinear flow field.

In this paper, they develop a new method that deals with this difficulty by extending the flow field into a linear global flow that best matches the data in the finite do- main, and allows trajectories to continue to separate once they cross the domain boundaries. With the new scheme trajectory, separations previously stopped prematurely are now recovered with the separation rate locked at their exit values and the artificial attractors are removed. Continue reading “Using Lagrangian Coherent Structures with atmospheric data”

Posted in MJO

Reorganization of Tropical Climate during El Niño

 

Benjamin R Lintner and John C H Chiang.

The applicability of a weak temperature gradient (WTG) formulation for the reorganization of tropical climate during El Niño–Southern Oscillation (ENSO) events is investigated. This idealized dynamical framework solves for the divergent portion of the tropical circulation by assuming a spatially homogeneous perturbation temperature profile and a mass balance constraint applied over the tropical belt. An inter- mediate-level complexity model [the Quasi-Equilibrium Tropical Circulation Model (QTCM)] configured with the WTG assumptions is used to simulate El Niño conditions and is found to yield an appropriate level of tropospheric warming, a plausible pattern of precipitation anomalies in the tropical Pacific source region of El Niño, and a gross precipitation deficit over the Tropics outside the Pacific (hereafter the “remote Tropics”). Continue reading “Reorganization of Tropical Climate during El Niño”

Posted in Articles, MJO

Madden, R. A. and P. R. Julian – Historical perspective of the MJO

Introduction

  • Quasibiennial Oscillation was “discovered” or described first in the in 1963 as steady features of the equatorial stratosphere by Ebdon(1963).
  • Yanai and Maruyama (1966) – wave like disturbances in the meridional wind, v, in tropical lower stratosphere with a timescale of five days, length scale of 10,000 km and westward phase speed of about 23 ms-1.
  • It was thought that such large-scale waves in the equatorial stratosphere was necessary for the momentum convergence needed to explain the QBO.
  • Matsuno (1966) published theoretical derivations for equatorial waves. Maruyama (1967) published results showing that the meridional signal was a mixed-Rossby gravity wave.
  • Wallace and Kousky (1968) found synoptic-scale 15-day period waves with length scales of 20,000-40,000 km (zonal wavenumber 2 and 1) and 6-10 km vertical scales. These were identified as Kelvin waves as predicted by Matsuno’s theory. Continue reading “Madden, R. A. and P. R. Julian – Historical perspective of the MJO”
Posted in Articles, MJO

Maloney, E. “The moist static energy budget of a composite tropical intraseasonal oscillation in a climate model.” Journal of Climate (2009).

The intraseasonal moist static energy (MSE) budget is analyzed in a climate model that produces realistic eastward-propagating tropical intraseasonal wind and precipitation variability. Consistent with the recharge– discharge paradigm for tropical intraseasonal variability, a buildup of column-integrated MSE occurs within low-level easterly anomalies in advance of intraseasonal precipitation, and a discharge of MSE occurs during and after precipitation when westerly anomalies occur. The strongest MSE anomalies peak in the lower troposphere and are, primarily, regulated by specific humidity anomalies. Continue reading “Maloney, E. “The moist static energy budget of a composite tropical intraseasonal oscillation in a climate model.” Journal of Climate (2009).”