广州降水与太阳活动及ENSO的关系

文章通过相关性计算得出,太阳黑子对广州降水的影响比南方涛动对广州降水的影响显著,相关系数分别为0．507和0．388,都通过了99％的显著性检验。同时,统计了1950年以来的ENSO事件,并与广州降水作了对应分析。得出结论,ENSO暖事件将使广州降水量减少;相反,ENSO冷事件则使广州降水量增加。     

Equilibrium Prices When the Sunspot Variable Is Continuous

We analyze sunspot-equilibrium prices in nonconvex economies with perfect markets and a continuous sunspot variable. Our primary result is that every sunspot equilibrium allocation can be supported by prices that, when adjusted for probabilities, are constant across states. This result extends to the case of a finite number of equally-probable states under a nonsatiation condition, but does not extend to general discrete state spaces. We use our primary result to establish the equivalence of the set of sunspot equilibrium allocations based on a continuous sunspot variable and the set of lottery equilibrium allocations. Journal of Economic Literature Classification Numbers: D51, D84, E32.     

Sunspots and Hopf bifurcations in continuous time endogenous growth models

First we treat a three-dimensional continuous time abstract stationary model that includes one predetermined variable and two non-predetermined variables. We construct stationary sunspot equilibria in this model under the following two alternative conditions: (i) a steady state has two stable roots and one unstable root; and (ii) A closed orbit has a two-dimensional manifold on which it is asymptotically stable. Next, we apply these results to the models due to Lucas and Romer that undergo Hopf bifurcations for some parameter values. We construct sunspot equilibria in these models.     

International capital flows,debt overhang and volatility

This paper shows how international capital flows originate boom‐bust and sunspot episodes in a neoclassical growth model of a small, open economy. A limit is imposed on how much the economy can borrow from foreign creditors and it is made endogenous by assuming that the debt‐to‐GDP ratio is procyclical. The steady state is locally indeterminate when the credit multiplier is larger than some threshold level, whereas saddle‐point stability prevails when the credit multiplier is low enough. As a consequence, high levels of the credit multiplier lead to both booms followed by busts and sunspot‐driven volatility near the steady state, while, in contrast, low levels ensure monotonic convergence. Compared with saddle‐path equilibria, boom‐bust and sunspot equilibria are associated with both lower welfare and debt overhang, that is, a crowding‐out effect of credit: when the economy is highly leveraged, it uses savings to cut down foreign debt, at the expense of both human and physical investment. Numerical examples show that indeterminacy arises for debt‐to‐GDP ratios that fall within the range of available estimates. Finally, the effects of shocks to the world interest rate on output and consumption are amplified and persistent in the debt overhang regime.     

Growth and Public Debt: What Are the Relevant Trade‐Offs?

The interplay between growth and public debt is addressed considering a Barro‐type (1990) endogenous growth model where public spendings are financed through taxes on income and public debt. The government has a target level of public debt relative to GDP, and the long‐run debt‐to‐GDP ratio is used as a policy parameter. We show that when debt is a large enough proportion of GDP, two distinct balanced‐growth paths (BGPs) may coexist, one being indeterminate. We exhibit two types of important trade‐offs associated with self‐fulfilling expectations. First, we show that the lowest BGP is always decreasing with respect to the debt‐to‐GDP ratio while the highest one is increasing. Second, we show that the highest BGP, which provides the highest welfare, is always locally indeterminate while the lowest is always locally determinate. Therefore, local and global indeterminacy may arise and self‐fulfilling expectations appear as a crucial ingredient to understand the impact of debt on growth, welfare, and macroeconomic fluctuations. Finally, a simple calibration exercise allows to provide an understanding of the recent experiences of many OECD countries.     

The spirit of capitalism, stock market bubbles and output fluctuations

This paper presents a representative agent model in which stock market bubbles cause output fluctuations. Assuming that utility depends directly on wealth, we show that stock market bubbles arise if the marginal utility of wealth does not decline to zero as wealth goes to infinity. Bubbles can affect output positively or negative depending on whether the production function exhibits increasing or decreasing returns to scale. In sunspot equilibria, the bursting of a bubble is followed by a sharp decline in output one period later. Various numerical examples are given to illustrate the behavior of stochastic bubbles and the relationship between bubbles and output.     

Multiple equilibria in a cash-in-advance two-sector economy

We consider a two-sector infinite horizon economy with a fractional cash-in-advance constraint on consumption expenditures. This formulation allows us to consider a steady-state velocity of money that is strictly greater than one and, therefore, provides a more plausible framework than the standard formulation in which all the consumption purchases are paid cash. We prove that the steady state is bound to be indeterminate and multiple equilibria occur when the share of the liquidity constraint is low enough and that a capital-intensive investment good or a strongly capital-intensive consumption good improve considerably the scope for indeterminacy. As a consequence, we show that without any restriction on the elasticity of intertemporal substitution in consumption, multiple equilibria might occur if the velocity of money is greater than a critical bound that is compatible with empirical estimates.     

A Characterization of Robust Sunspot Equilibria

In nonconvex environments, a sunspot equilibrium can sometimes be destroyed by the introduction of new extrinsic information. We provide a simple test for determining whether or not a particular equilibrium survives, or is robust to, all possible refinements of the state space. We use this test to provide a characterization of the set of robust sunspot-equilibrium allocations of a given economy; it is equivalent to the set of equilibrium allocations of the associated lottery economy. Journal of Economic Literature Classification Numbers: D51, D84, E32.     

International transmission of bubble crashes in a two-country overlapping generations model

We study the international transmission of bubble crashes by analyzing stationary sunspot equilibria in a two-country overlapping generations exchange economy with stochastic bubbles. We consider two cases of sunspot shocks. In the first case, we assume that only the foreign country receives a sunspot shock, while in the second, we assume that both countries independently receive sunspot shocks. In the first case, a bubble crash in the foreign country is always accompanied by a bubble crash in the home country. In the second case, a bubble crash in the foreign country can have a positive or negative effect on the home bubble. We also show that there exists a unique locally isolated stationary sunspot equilibrium, and that it is locally unstable.