A multipoint study of a substorm occurring on 7 December, 1992, and its theoretical implications

On 7 December 1992, a moderate substorm was observed by a variety of satellites and ground-based instruments. Ionospheric flows were monitored near dusk by the Goose Bay HF radar and near midnight by the EISCAT radar. The observed flows are compared here with magnetometer observations by the IMAGE array in Scandinavia and the two Greenland chains, the auroral distribution observed by Freja and the substorm cycle observations by the SABRE radar, the SAMNET magnetometer array and LANL geosynchronous satellites. Data from Galileo Earth-encounter II are used to estimate the IMF B-z component. The data presented show that the substorm onset electrojet at midnight was confined to closed field lines equatorward of the preexisting convection reversal boundaries observed in the dusk and midnight regions. No evidence of substantial closure of open flux was detected following this substorm onset. Indeed the convection reversal boundary on the duskside continued to expand equatorward after onset due to the continued presence of strong southward IMF, such that growth and expansion phase features were simultaneously present. Clear indications of closure of open flux were not observed until a subsequent substorm intensification 25 min after the initial onset. After this time, the substorm auroral bulge in the nightside hours propagated well poleward of the pre-existing convection reversal boundary, and strong flow perturbations were observed by the Goose Bay radar, indicative of flows driven by reconnection in the tail.

Echoes of 1992: the NAFTA negotiations and North America now

Two decades ago, Canada, Mexico, and the United States created a continental economy. The road to integration from the signing of the North American Free Trade Agreement has not been a smooth one. Along the way, Mexico lived through a currency crisis, a democratic transition, and the rising challenge of Asian manufacturing. Canada stayed united despite surging Quebecois nationalism during the 1990s; since then, it has seen dramatic economic changes with the explosion of hydrocarbon production and a much stronger currency. The United States saw a stock-market bust, the shock of 9/11, and the near-collapse of its financial system. All of these events have transformed the relationships that emerged after NAFTA entered into force in 1994. Given the tremendous changes, one might be skeptical that the circumstances and details of the negotiation and ratification of NAFTA hold lessons for the future of North America. However, the road to NAFTA had its own difficulties, and many of the issues involved in the negotiations underpin today's challenges. NAFTA was conceived at a time of profound change in the international system. When Mexican leaders surveyed the world two decades ago, they saw emerging regional groupings in Europe, Asia, and South America. Faced with a lack of interest or compatibility, they instead doubled down on North America. How did Mexican leaders reconsider their national interests and redefine Mexico's role in the world in light of those transformations? Unpublished Mexican documents from SECOFI, the secretariate most involved in negotiating NAFTA, help illustrate Mexican thinking about its interests and role at that time. Combining those insights with analysis of newly available evidence from U.S. presidential archives, this paper sheds light on the negotiations that concluded two decades ago.

Variability and trends in Laptev Sea ice outflow between 1992-2011

Variability and trends in seasonal and interannual ice area export out of the Laptev Sea between 1992 and 2011 are investigated using satellite-based sea ice drift and concentration data. We found an average total winter (Octo- ber to May) ice area transport across the northern and east- ern Laptev Sea boundaries (NB and EB) of 3.48 × 10 5 km 2 . The average transport across the NB (2.87 × 10 5 km 2 ) is thereby higher than across the EB (0.61 × 10 5 km 2 ), with a less pronounced seasonal cycle. The total Laptev Sea ice area flux significantly increased over the last decades (0.85 × 10 5 km 2 decade − 1 , p> 0 . 95), dominated by increas- ing export through the EB (0.55 × 10 5 km 2 decade − 1 , p> 0 . 90), while the increase in export across the NB is smaller (0.3 × 10 5 km 2 decade − 1 ) and statistically not significant. The strong coupling between across-boundary SLP gradient and ice drift velocity indicates that monthly variations in ice area flux are primarily controlled by changes in geostrophic wind velocities, although the Laptev Sea ice circulation shows no clear relationship with large-scale atmospheric in- dices. Also there is no evidence of increasing wind velocities that could explain the overall positive trends in ice export. The increased transport rates are rather the consequence of a changing ice cover such as thinning and/or a decrease in con- centration. The use of a back-propagation method revealed that most of the ice that is incorporated into the Transpolar Drift is formed during freeze-up and originates from the cen- tral and western part of the Laptev Sea, while the exchange with the East Siberian Sea is dominated by ice coming from the central and southeastern Laptev Sea. Furthermore, our re- sults imply that years of high ice export in late winter (Febru- ary to May) have a thinning effect on the ice cover, which in turn preconditions the occurence of negative sea ice extent anomalies in summer.