1.   Investors expect the Federal Reserve will soon act to raise interest rates.

2.   When traders sell the currency in large volumes, the board can act to raise interbank interest rates, which draws dollars back into the system.

3.   Higher rates would trim economic growth but they would also act to raise the value of the yen against other currencies by increasing the yield on investments in yen.

4.   Other governments want the United States to act to raise the value of the dollar, which has been declining all this year.