Impact of Solar Wind Depression on the Dayside Magnetosphere under Northward Interplanetary Magnetic Field

We present a follow up study of the sensitivity of the Earth's magnetosphere to solar wind activity using a particles-in-cell model [Baraka and Ben Jaffel, 2007], but here during northward IMF. The formation of the magnetospheric cavity and its elongation is obtained with the classical structure of a magnetosphere with parallel lobes. An impulsive disturbance is then applied to the system by changing the bulk velocity of the solar wind to simulate a decrease in the solar wind dynamic pressure followed by its recovery. In response to the imposed disturbance, a gap [abrupt depression] in the incoming solar wind plasma appears moving toward the Earth. The gap's size is a ~15 RE and is comparable to the sizes previously obtained for both Bz<0 and Bz =0. During the initial phase of the disturbance, the dayside magnetopause (MP) expands slower than the previous cases of IMF orientations as a result of the depression. The size of the MP expands nonlinearly due to strengthening of its outer boundary by the northward IMF. Also, during the initial 100 {\Delta}t, the MP shrank down from 13.3 RE to ~9.2 RE before it started expanding; a phenomenon that was also observed for southern IMF conditions but not during the no IMF case. As soon as they felt the solar wind depression, cusps widened at high altitude while dragged in an upright position. For the field's topology, the reconnection between magnetospheric and magnetosheath fields is clearly observed in both northward and southward cusps areas. Also, the tail region in the northward IMF condition is more confined, in contrast to the fishtail-shape obtained in the southward IMF case. An X-point is formed in the tail at ~110 RE compared to ~103 RE and ~80 RE for Bz =0 and Bz <0 respectively. Our findings are consistent with existing reports from many space observatories for which predictions are proposed to test furthermore our simulation technique.Comment: 48 pages, 6 figures, 1 table, accepted for publication in Annales Geophysicae (ANGEO Communicates

Permanent Income, Liquidity, and Expenditure on Automobiles: Evidence from Panel Data

Several recent papers have tested the permanent income-cum- rational expectations hypothesis using data on nondurable or semi-durable consumption. We show how this approach can be extended to the case of durables. An application to panel data on automobile expenditures reveals no evidence against the permanent income hypothesis. This result is unchanged in subsamples segregated by family holdings of liquid assets.

On theories of random variables

We study theories of spaces of random variables: first, we consider random variables with values in the interval $[0,1]$, then with values in an arbitrary metric structure, generalising Keisler's randomisation of classical structures. We prove preservation and non-preservation results for model theoretic properties under this construction: i) The randomisation of a stable structure is stable. ii) The randomisation of a simple unstable structure is not simple. We also prove that in the randomised structure, every type is a Lascar type

The Macroeconomics of the Great Depression: A Comparative Approach

Recently, research on the causes of the Great Depression has shifted from a heavy emphasis on events in the United States to a broader, more comparative approach that examines the interwar experiences of many countries simultaneously. In this lecture I survey the current state of our knowledge about the Depression from a comparative perspective. On the aggregate demand side of the economy, comparative analysis has greatly strengthened the empirical case for monetary shocks as a major driving force of the Depression; an interesting possibility suggested by this analysis is that the worldwide monetary collapse that began in 1931 may be interpreted as a jump from one Nash equilibrium to another. On the aggregate supply side, comparative empirical studies provide support for both induced financial crisis and sticky nominal wages as mechanisms by which nominal shocks had real effects. Still unresolved is why nominal wages did not adjust more quickly in the face of mass unemployment.

Irreversibility, Uncertainty, and Cyclical Investment

The optimal timing of real investment is studied under the assumptions that investment is irreversible and that new information about returns is arriving over time. Investment should be undertaken in this case only when the costs of deferring the project exceed the expected value of information gained by waiting. Uncertainty, because it increases the value of waiting for new information, retards the current rate of investment. The nature of investor's optimal reactions to events whose implications are resolved over time is a possible explanation of the instability of aggregate investment over the business cycle.

By the numbers: data and measurement in community economic development

Highlights of a speech by Federal Reserve Chairman Ben S. Bernanke at the Greenlining Institute’s 13th Annual Economic Development Summit in Los Angeles, April 20, 2006.Community development

The sensitivity of empirical studies to alternative measures of the monetary base and reserves - commentary

Money supply ; Bank reserves

Adjustment Costs, Durables, and Aggregate Consumption

Previous tests of the permanent income hypothesis (PIH) have focused on either nondurables or durables expenditures in isolation. This paper studies consumer purchases of nondurables and durables as the outcome of a single optimization problem.It is shown that the presence of adjustment costs of changing durables stocks may substantially affect the time series properties of both components of expenditure under the PIH.However, econometric tests based on this model do not contradict earlier rejections of the PIH in aggregate quarterly data.