4:00 PM - 4:15 PM
[AAS10-09] An analysis of long-period fluctuation of atmospheric angular momentum and its mechanism
Keywords:Atmospheric angular momentum, atmospheric waves
Atmospheric angular momentum (AAM) fluctuations are considered to have high predictability, thus, it is important for weather prediction and climate projection. Moreover, AAM fluctuations modify the speed of the Earth's rotation and the length of day, which cause significant impact on geodetic technology such as GNSS. Thus, it is important to understand the mechanism of the AAM fluctuation.
The period of AAM fluctuations ranges from tens of days to several years. Particularly, previous studies pointed out the relation with ENSO at the interannual scales.
The phase of AAM fluctuations often propagates from the tropics to mid-high latitudes. Several mechanisms have been proposed for this feature, in term of the momentum flux, although it is still controversy. In particular, what kind of atmospheric waves give the momentum flux is not clear. Therefore, the purpose of this study is to elucidate the waves that are responsible to the AAM fluctuations and the generation mechanism of AAM anomaly.
In this study, we used two kind of reanalysis datasets (MERRA-2, JRA-55), and outputs of d4PDF historical climate simulations. The latter is composed of 100 members. Thus, we can capture statistically significant features by taking the ensemble mean. Analyzed time period is from January 1951 to December 2011 for d4PDF. First, we confirmed the consistency with previous studies on the anomaly of AAM integrated vertically from 100 hPa to 750 hPa, where anomaly was defined as the difference from the climatology for each calendar day. Similarly, we calculated EP-flux divergence (EPFD) anomaly.
We first confirmed that the AAM fluctuations propagate poleward and as it follows, the poleward propagation of EPFD as is consistent with previous studies. Particularly, AAM and EPFD exhibited large values near the latitude of 20 ° ~ 30° during the poleward propagation. We also found that AAM and EPFD fluctuations have a positive correlation with ENSO index. In a presentation, we will show the result of EPFD calculated for three regions, which respectively contain the Pacific, Atlantic, and Indian Oceans.
The period of AAM fluctuations ranges from tens of days to several years. Particularly, previous studies pointed out the relation with ENSO at the interannual scales.
The phase of AAM fluctuations often propagates from the tropics to mid-high latitudes. Several mechanisms have been proposed for this feature, in term of the momentum flux, although it is still controversy. In particular, what kind of atmospheric waves give the momentum flux is not clear. Therefore, the purpose of this study is to elucidate the waves that are responsible to the AAM fluctuations and the generation mechanism of AAM anomaly.
In this study, we used two kind of reanalysis datasets (MERRA-2, JRA-55), and outputs of d4PDF historical climate simulations. The latter is composed of 100 members. Thus, we can capture statistically significant features by taking the ensemble mean. Analyzed time period is from January 1951 to December 2011 for d4PDF. First, we confirmed the consistency with previous studies on the anomaly of AAM integrated vertically from 100 hPa to 750 hPa, where anomaly was defined as the difference from the climatology for each calendar day. Similarly, we calculated EP-flux divergence (EPFD) anomaly.
We first confirmed that the AAM fluctuations propagate poleward and as it follows, the poleward propagation of EPFD as is consistent with previous studies. Particularly, AAM and EPFD exhibited large values near the latitude of 20 ° ~ 30° during the poleward propagation. We also found that AAM and EPFD fluctuations have a positive correlation with ENSO index. In a presentation, we will show the result of EPFD calculated for three regions, which respectively contain the Pacific, Atlantic, and Indian Oceans.