A search for the seasonal variability on the depositional fluxes of 7Be and 210Pb
A search for the seasonal variability on the depositional fluxes of 7Be and 210Pb
复制标题
DOI：
10.1029/94jd02824
复制
发表时间：
1995-02
影响因子：
--
通讯作者：
M. Baskaran
中科院分区：
文献类型：
--
作者：
M. Baskaran
对全球许多地方7Be和210Pb大气沉降物的调查表明，这两种核素的沉降通量存在季节变化，少数地方冬季高，而大多数地方在春季高。然而，这些早期的研究并没有定量地处理这些时期降水量的相应季节变化。1989-1991年加尔维斯顿地区7Be和210Pb的沉积通量数据表明，该地区7Be和210Pb的季节变化不均匀，降水量主要控制其沉积通量。所有最近发表的关于这些放射性核素的沉积通量的数据都被合成。此外，还讨论了7Be和210Pb沉积通量的季节变化，这是由于季节降水的变化引起的。研究表明，7Be和210Pb在秋季的沉降通量最小，大部分时间的沉降通量最大值局限于春季和夏季。这些核素的沉积通量的季节间变化并不保持不变。本文所提供的数据与先前发表的数据相结合似乎表明，观测到的春季7Be沉积通量的季节性增加不是由于该季节对流层-平流层气团交换所致。7Be/ 210Pb活度比值在夏季保持最高，这是由于夏季对流层稳定性下降导致7Be（从对流层上层到对流层中下层）和210Pb（从对流层下层到对流层上层）垂直输送速率增加所致。
Investigations of the atmospheric fallout of 7Be and 210Pb in many places around the globe indicate that there are seasonal variations on the depositional fluxes of these nuclides: high in winter in a few places, while in most places the high occurs in spring. However, these earlier studies did not address quantitatively the corresponding seasonal variations of the amount of precipitation during these periods. Data on the depositional fluxes of 7Be and 210Pb in Galveston, Texas, during the years 1989–1991 indicate that the seasonal variation is not uniform from year to year, and the amount of precipitation primarily controls the depositional fluxes. All the recently published data on the depositional fluxes of these radionuclides to date are synthesized. Also, the seasonal variations of the depositional fluxes of 7Be and 210Pb due to the variations in the amounts of precipitation during these seasons are discussed. This study clearly shows that the depositional fluxes of 7Be and 210Pb during fall were minimum, and most of the time the fallout maxima were confined to either spring and/or summer. Interseasonal variations of the depositional fluxes of these nuclides do not remain the same. The data presented in this paper in conjunction with earlier published data seem to indicate that the observed seasonal increase in the depositional fluxes of 7Be during spring is not due to the troposphere-stratosphere exchange of air masses during that season. The 7Be/ 210Pb activity ratio values remain the highest in summer and this is attributed to the increased rate of vertical transport of 7Be (from the upper troposphere to the middle and lower troposphere) and 210Pb (from the lower troposphere to upper troposphere) due to decreased stability of the troposphere during summer months.