Geophysical and Astrophysical Fluid Dynamics

Abstract:

In this paper we derive a reduced-order approximation to the vertical and horizontal structure of a simplified model of the baroclinically unstable Martian atmosphere. The original model uses the full hydrostatic primitive equations on a sphere, but has only highly simplified schemes to represent the detailed physics of the Martian atmosphere, e.g. forcing towards a plausible zonal mean temperature state using Newtonian cooling. Three different norms are used to monitor energy conversion processes in the model and are then compared. When four vertical modes (the barotropic and first three baroclinic modes) are retained in the reduced-order approximation, the correlation norm captures approximately 90% of the variance, while the kinetic energy and total energy norms capture approximately 83% and 78% of the kinetic and total energy respectively. We show that the leading order Proper Orthogonal Decomposition (POD) modes represent the dominant travelling waves in the baroclinically-unstable, winter hemisphere. In part 2 of our study we will develop a hierarchy of truncated POD-Galerkin expansions of the model equations using up to four vertical modes. © 2005 Author(s). This work is licensed under a Creative Commons License.

Abstract:

The Composite Infrared Spectrometer (CIRS) is a remote-sensing Fourier Transform Spectrometer (FTS) on the Cassini orbiter that measures thermal radiation over two decades in wavenumber, from 10 to 1400 cm- 1 (1 mm to 7μ m), with a spectral resolution that can be set from 0.5 to 15.5 cm- 1. The far infrared portion of the spectrum (10-600 cm - 1) is measured with a polarizing interferometer having thermopile detectors with a common 4-mrad field of view (FOV). The middle infrared portion is measured with a traditional Michelson interferometer having two focal planes (600-1100 cm- 1, 1100-1400 cm- 1). Each focal plane is composed of a 1× 10 array of HgCdTe detectors, each detector having a 0.3-mrad FOV. CIRS observations will provide three-dimensional maps of temperature, gas composition, and aerosols/condensates of the atmospheres of Titan and Saturn with good vertical and horizontal resolution, from deep in their tropospheres to high in their mesospheres. CIRS's ability to observe atmospheres in the limb-viewing mode (in addition to nadir) offers the opportunity to provide accurate and highly resolved vertical profiles of these atmospheric variables. The ability to observe with high-spectral resolution should facilitate the identification of new constituents. CIRS will also map the thermal and compositional properties of the surfaces of Saturn's icy satellites. It will similarly map Saturn's rings, characterizing their dynamical and spatial structure and constraining theories of their formation and evolution. The combination of broad spectral range, programmable spectral resolution, the small detector fields of view, and an orbiting spacecraft platform will allow CIRS to observe the Saturnian system in the thermal infrared at a level of detail not previously achieved. © 2004 Kluwer Academic Publishers.

Abstract:

A series of analyses combining feature-tracking from visible images and infrared sounding observations obtained by Voyager I and 2 are presented for the region surrounding Jupiter's Great Red Spot. By making use of various dynamical balance constraints, fully three-dimensional maps of a number of meteorological variables (such as horizontal wind, isobaric geopotential height and vertical velocity) can be recovered. Such maps are of immense potential value in a variety of studies of atmospheres such as those of the outer planets, and some possible extensions of this approach to ongoing and future spacecraft missions are discussed. (c) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.

Abstract:

A new general circulation model (GCM) of Venus is being developed at Oxford. Venus presents unique numerical and physical challenges because of its thick atmosphere, slow underlying solid body rotation, and super-rotating atmosphere. Preliminary results from a GCM with simplified physical parameterizations are discussed. The current model uses linearized cooling and friction schemes, and spans five decades of pressure (0-90 km). The model is able to demonstrate significant global super-rotation, and although not yet fully realistic, future plans include more detailed representation of the Venusian atmosphere, such as the planetary boundary layer (PBL) scheme. The use of the model is discussed in supporting and interpreting data from future missions to Venus. (c) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.

Abstract:

We study the interannual variability of dust storms on Mars in an assimilation of thermal profiles and dust opacity observations into a general circulation model for the Martian atmosphere. The observations have been provided by the thermal emission spectrometer aboard the Mars Global Surveyor spacecraft during the scientific mapping phase over more than two complete Martian years, which include three dusty seasons in southern spring. A comparison between dust seasons which are characterized only by regional storms and the global, planet-encircling dust storm of 2001 is performed, focusing on the meteorological conditions which can trigger the onset and development of the global storm, and its effects on the global circulation. (c) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.