Geophysical Research Letters

Natarajan, Murali; Remsberg, Ellis E.; Gordley, Larry L.

doi: 10.1029/2001GL014262pmid: N/A

Recently reprocessed LIMS dataset has been used with a contemporary photochemical model to study the balance between photochemical production and destruction of ozone in the upper stratosphere. Model results corresponding to January 1979 indicate that the ozone deficit is less than 15% in the pressure range of 5 to 0.5 mb between 50°S and 50°N latitude. The imbalance at 40 km is much smaller than reported by the earliest studies with the archived LIMS data. The same model, when initialized with HALOE (version 19) data for January, 1996, shows similar results with peak ozone deficits being less than 10%. For both cases, the model shows a near balance in the ozone budget above 1 mb, contrary to recent studies based on balloon‐borne measurements. The magnitude of the ozone imbalance seen in this study is within the uncertainties of the data and model.

Carmeliet, J.; Van Den Abeele, Koen EA.

doi: 10.1029/2001GL014243pmid: N/A

Experimental evidence for the saturation dependence of the nonlinear behavior of Berea sandstone has been analyzed using the Preisach‐Mayergoyz space (P‐M space) model in terms of classical and non‐classical mesoscopic entities. The analysis suggests the introduction of two macroscopic solid‐fluid interaction pressures, which link the moisture influence to characteristic populations of the material composition.

Lowe, D. C.; Levchenko, V. A.; Moss, R. C.; Allan, W.; Brailsford, G. W.; Smith, A. M

doi: 10.1029/2002GL014719pmid: N/A

We draw attention to an effect that has the potential to compromise measurements of atmospheric 14CO by the in situ production of 14C in air sample cylinders. We present first experimental determinations of the size of this effect using measurements made on cylinders containing an air sample and a CO/nitrogen calibration gas stored in laboratories in New Zealand from a few months to 11 years. These data are collated with measurements made on air samples stored at Scott Base, Antarctica to determine a mean in situ production rate for 14CO of 4.7 ± 0.5 molecules cm−3 yr−1 (STP) at sea level and in the latitude range 40–90° (geomagnetic) in a single floor laboratory. This rate is significant compared to observed annual cycles in 14CO (typically 5–10 14CO molecules cm−3) caused by OH variations and clearly has to be corrected for when 14CO data are used to determine atmospheric OH distributions.

Ferré, Eric C.

doi: 10.1029/2001GL014367pmid: N/A

Multi‐domain magnetites display a normal anisotropy of magnetic susceptibility (AMS) fabric where grain shape axes coincide with AMS axes. By contrast, single‐domain magnetite has an inverse magnetic fabric where magnetic axes are interchanged. The mixing of normal and inverse magnetic fabrics results in intermediate fabrics. Theoretical models for intermediate fabrics consider all combinations of normal and inverse fabrics. The minimum amount of inverse component required for intermediate fabrics to form is about 20% in the case of prolate normal (T = −0.50) and prolate inverse (T = −0.42) components. Such a small amount of inverse component may not be noticed. The anisotropy resulting from intermediate fabrics is lower than that of the normal or inverse contribution to AMS. This suggests that whenever intermediate fabrics occur neither the shape factor nor the degree of anisotropy relate to strain in a simple way.

Posner, Arik; Schwadron, Nathan A.; Zurbuchen, Thomas H.; Kozyra, Janet U.; Liemohn, Michael W.; Gloeckler, George

doi: 10.1029/2001GL013449pmid: N/A

We present the first study of Low‐Charge‐State Heavy Ion (LCSHI) events covering a region from Earth's bow shock to the L1 point, obtained with the Suprathermal Ion Composition Spectrometer onboard Wind. STICS is capable of distinguishing charge states of suprathermal ions. In 1995–2000 we found a large number of particle events revealing species of magnetospheric origin. LCSHI events tend to occur in series and in connection with geomagnetic activity. The occurrence rate is found to increase towards solar maximum. The spatial region covered by this particle population ranges from the bow shock to beyond distances of 130 Re, where one of the strongest events occurred. Based on the characterization of LCSHI events we discuss mechanisms for their formation. We conclude that the most probable sources of these ion events are substorms in association with Alfvén waves in high‐speed solar wind streams and the magnetic storm recovery ring current.

Nonaka, Masami; Xie, Shang‐Ping; McCreary, Julian P.

doi: 10.1029/2001GL013717pmid: N/A

A mechanism for generating decadal sea surface temperature (SST) variability in the equatorial Pacific is investigated using an ocean general circulation model forced by observed wind stress. Equatorial SST variability is governed by different ocean dynamics on interannual and decadal time scales. At interannual time scales, equatorial SST anomalies are mainly driven by equatorial winds. At decadal time scales, on the other hand, they are forced both by equatorial winds and by off‐equatorial winds in the tropics, while the contribution from midlatitude winds poleward of 25° is negligible. Trade‐wind variations in the off‐equatorial tropics force equatorial SST variability by spinning up and down the subtropical cells that transport cold water into the equatorial upwelling zone. Equatorial SST anomalies induced by this mechanism lag behind the response to local equatorial winds by about two years.

May, Wilhelm

doi: 10.1029/2001GL013808pmid: N/A

In this study the possible change of the Indian summer monsoon associated with the anticipated increase in the greenhouse gases concentrations is investigated. This is done on the basis of a time‐slice experiment performed with the ECHAM4 atmospheric GCM at a high horizontal resolution of T106. The first time‐slice (1970–1999) represents the present‐day climate and the second one (2060–2089) the future climate. The time‐slice experiment predicts an intensification of the rainfall in the Indian region during the monsoon season due to the general warming, while the future changes in the large‐scale flow indicate a weakening of the monsoon circulation. The increase of the regional rainfall is related to an intensification of the atmospheric moisture transport into the Indian region.

Woch, Joachim; Krupp, Norbert; Lagg, Andreas

doi: 10.1029/2001GL014080pmid: N/A

In the magnetosphere of Jupiter the plasma convection is driven by the planetary rotation up to considerable distances from the planet. However, at larger distances the rotational flow is often disrupted by explosive events, seen as jets of energetic particles propagating in the radial direction. These events are observed very frequently and can be regarded as an intrinsic property of the Jovian system. A statistical survey shows that the burst events are concentrated in the post‐midnight tail region. Inward directed bursts dominate closer to the planet, outward directed bursts further away from the planet. The transition from mainly inward to mainly outward directed bursts defines the most probable location of a near‐Jupiter neutral line. The findings corroborate early models which postulate that magnetic flux tubes heavily loaded with plasma originating from the moon Io will be stretched by the centrifugal forces up to such a degree that spontaneous reconnection sets in. This leads to acceleration of plasma and the release of plasmoids into interplanetary space. The process may also drive the recently observed auroral dawn storms at Jupiter.

Yoshikawa, Akimasa

doi: 10.1029/2001GL014125pmid: N/A

It has been well recognized that field‐aligned current (FAC) systems lose their energy in the ionosphere through the Joule dissipation that is caused by their closure via the ionospheric Pedersen current, and that the ionospheric Hall current cannot contribute the total energy dissipation. However, it is also true that the rotational Hall current is excited by the incident FAC, and it radiates a Poynting vector that grows a poloidal‐type magnetic field. Even if the Hall effect cannot do work on an external system, what does its contribution to the accumulation of poloidal magnetic energy really mean? In this paper, it is clarified that the divergent Hall current, excited during the transient phase of magnetosphere‐ionosphere coupling, closes via the FAC and produces a Hall current generator, which pumps up the energy of the FAC system to increase the ionospheric rotational Hall current (together with its associated poloidal magnetic field).

Busse, F. H.

doi: 10.1029/2001GL014597pmid: N/A

A simple model based on the rotating cylindrical annulus configuration is presented which demonstrates that two different sources of buoyancy one of which is characterized by a very low diffusivity can interact such that the latter balances the non‐geostrophic part of the Coriolis force. It is suggested that the concentration of light elements in the Earth's core could play this role thereby facilitating immensely convection driven by thermal buoyancy.