Impacts of ENSO and IOD on Snow Depth over the Tibetan Plateau: Roles of Convections over the Western North Pacific and Indian Ocean

2020 ◽  
Author(s):  
Tuantuan Zhang ◽  
Xingwen Jiang ◽  
Chi-Yung Tam ◽  
Junwen Chen ◽  
Ngar-Cheung Lau ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Tibetan Plateau ◽  
North Pacific ◽  
Snow Depth ◽  
Western North Pacific ◽  
Cyclonic Circulation ◽  
Cold Temperature ◽  
The Tibetan Plateau ◽  
The Tropics ◽  
Anomalous Cyclonic Circulation

<p>This is a consensus that snow over the Tibetan Plateau (TP) modulates the regional climate significantly. Possible causes for the interannual variability of snow over the TP, however, are under debate, especially regarding the independent roles of El Niño-Southern (ENSO) and Indian Ocean dipole (IOD). Based on in-situ observational data analyses and model simulations, our study shows that impacts of ENSO and IOD on snow depth (SD) over the TP are different during early winter. In particular, ENSO mostly affects SD over the eastern TP, while IOD affects SD over the central-western TP. Both above-normal snowfall and cold temperature anomaly contribute to deeper-than-normal SD, with the former playing a more important role. Diabatic cooling of the suppressed convection over the western North Pacific that related to the positive phase of ENSO could excite an anomalous cyclonic circulation and strong cold temperature anomalies over the eastern TP. There is an enhanced moisture transported over the eastern TP from the tropics due to the anomalous cyclonic circulation; along with strong cold temperature anomalies, resulting in above-normal snowfall in the eastern TP. On the other hand, anomalous convection over the western Indian Ocean related to the positive IOD could generate a wave-train propagating northeastward and induce an anomalous cyclonic circulation over the central-western TP. The associated anomalous circulation transports extra moisture from the tropics to the central-western TP, providing conditions favorable for more snowfall over the central-western TP. Opposite conditions tend to occur during negative phases of ENSO and IOD.</p>

Impacts of ENSO and IOD on Snow Depth Over the Tibetan Plateau: Roles of Convections Over the Western North Pacific and Indian Ocean

2019 ◽  
Vol 124 (22) ◽  
pp. 11961-11975 ◽  
Author(s):  
Xingwen Jiang ◽  
Tuantuan Zhang ◽  
Chi‐Yung Tam ◽  
Junwen Chen ◽  
Ngar‐Cheung Lau ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Tibetan Plateau ◽  
North Pacific ◽  
Snow Depth ◽  
Western North Pacific ◽  
The Tibetan Plateau

scholarly journals Interdecadal change in the genesis activity of the first tropical cyclone of each year over the western North Pacific

2021 ◽  
Author(s):  
Yumi Cha ◽  
JaeWon Choi ◽  
Joong-Bae Ahn
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Walker Circulation ◽  
The Philippines ◽  
Cyclonic Circulation ◽  
Equatorial Pacific ◽  
Trade Winds ◽  
Anticyclonic Circulation ◽  
Anomalous Cyclonic Circulation

Abstract This study analyzed time series of the genesis latitude, longitude, and date of the first tropical cyclone (TC) each year over the 38 years between 1979 and 2016. Statistical change-point analysis applied to these three variables showed that a shift in climate regime occurred around 1998. More specifically, recent TCs have shown a strong tendency to occur more northwest in the western North Pacific (WNP), and day of TC genesis tend to be delayed. Also, we compared differences between the periods 1998 to 2016 (post-1998) and 1979–1997 (pre-1998) in terms of outgoing longwave radiation (OLR), total cloud cover, precipitable water, precipitation, vertical wind shear, 850 hPa relative vorticity, and sea surface temperature (SST). Our results showed that a favorable environment for TC genesis was formed near the South China Sea (SCS) and the Philippines and an unfavorable environment for TC genesis was formed in the southeastern part of the WNP. Analysis of stream flow showed that an anomalous cyclonic circulation at 850 hPa was formed in the SCS and an anomalous large anticyclonic circulation was formed in the North Pacific. From these circulations, a ridge extended to the east sea of the Philippines, and consequently, anomalous trade winds were strengthened in the equatorial Pacific. Such anomalous atmospheric circulation seems to be associated with the cold Pacific Decadal Oscillation (PDO) phase. At 200 hPa, the anomalous anticyclonic circulation was strengthened in the SCS, and an anomalous cyclonic circulation formed in the east sea of the Philippines, which strengthened anomalous westerlies in the equatorial Pacific. Furthermore, this circulation pattern is found to be related with a strengthening of Walker circulation. Therefore, during the post-1998, when trade winds were strengthened by the development of Walker circulation, the cold PDO phase was strengthened, the location of TC genesis moved toward the northwestern WNP, and TC genesis day tended to be delayed.

Enhanced predictability of rapidly intensifying tropical cyclones over the western North Pacific associated with snow depth changes over the Tibetan Plateau

2022 ◽  
pp. 1-45
Author(s):  
Xiang Han ◽  
Haikun Zhao ◽  
Philip J. Klotzbach ◽  
Liguang Wu ◽  
Graciela B. Raga ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Tropical Cyclones ◽  
North Pacific ◽  
Snow Depth ◽  
Decadal Variability ◽  
The Tibetan Plateau ◽  
Circulation Anomaly ◽  
Anticyclonic Circulation ◽  
Westerly Jet ◽  
The Relationship

Abstract This study finds an enhanced relationship in recent years between January–March eastern Tibetan Plateau snow depth (TPSD) and the frequency of rapidly intensifying tropical cyclones (RITCs) over the western Northern Pacific (WNP) during the following peak TC season (July–November). The correlation between TPSD and RITCs is significant during 2000–2014 but was insignificant from 1979–1999. During 2000–2014, when TPSD increases, there is an enhanced low-level anomalous anticyclone over the subtropical eastern North Pacific mainly due to the combined effect of advection and dynamics of the climatological prevailing westerly jet. Northeasterly wind anomalies are observed on the flank of the anticyclonic circulation anomaly, favoring anomalously cool sea surface temperature (SST). These anomalies lead to an anomalous pattern similar to the Pacific meridional mode (PMM), via a wind-evaporation feedback and cold advection. A Gill-type Rossby response to the PMM-like negative phase results in an anticyclonic circulation anomaly over the WNP, suppressing RITCs during 2000–2014. A nearly opposite circulation anomaly occurred when TPSD was lower during 2000–2014. There is a weak relationship between TPSD and RITCs, due to the lack of a link between TPSD and the PMM-like pattern from 1979–1999. Decadal changes in the relationship between TPSD and RITCs are mainly due to the meridional displacement of the prevailing westerly jet which may be in response to decadal-to-multi-decadal variability of SST anomalies. These changes then result in changes in the relationship between January–March TPSD and the PMM-like pattern.

scholarly journals Spatio-Temporal Variation Characteristics of Snow Depth and Snow Cover Days over the Tibetan Plateau

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 307
Author(s):  
Chi Zhang ◽  
Naixia Mou ◽  
Jiqiang Niu ◽  
Lingxian Zhang ◽  
Feng Liu
Keyword(s):  
Tibetan Plateau ◽  
Snow Cover ◽  
Snow Depth ◽  
Feedback Effect ◽  
Effect Of Temperature ◽  
The Tibetan Plateau ◽  
Reanalysis Dataset ◽  
Spatio Temporal ◽  
The Impact ◽  
Main Factor

Changes in snow cover over the Tibetan Plateau (TP) have a significant impact on agriculture, hydrology, and ecological environment of surrounding areas. This study investigates the spatio-temporal pattern of snow depth (SD) and snow cover days (SCD), as well as the impact of temperature and precipitation on snow cover over TP from 1979 to 2018 by using the ERA5 reanalysis dataset, and uses the Mann–Kendall test for significance. The results indicate that (1) the average annual SD and SCD in the southern and western edge areas of TP are relatively high, reaching 10 cm and 120 d or more, respectively. (2) In the past 40 years, SD (s = 0.04 cm decade−1, p = 0.81) and SCD (s = −2.3 d decade−1, p = 0.10) over TP did not change significantly. (3) The positive feedback effect of precipitation is the main factor affecting SD, while the negative feedback effect of temperature is the main factor affecting SCD. This study improves the understanding of snow cover change and is conducive to the further study of climate change on TP.

scholarly journals Change in Tropical Cyclone Activity during the Break of the Western North Pacific Summer Monsoon in Early August

2016 ◽  
Vol 29 (7) ◽  
pp. 2457-2469 ◽  
Author(s):  
Ke Xu ◽  
Riyu Lu
Keyword(s):  
Tropical Cyclone ◽  
Summer Monsoon ◽  
North Pacific ◽  
Western North Pacific ◽  
Cyclonic Circulation ◽  
Tropical Cyclone Activity ◽  
Upward Motion ◽  
Mariana Islands ◽  
Cyclone Activity

Abstract The modulation of tropical cyclone (TC) activity by the western North Pacific (WNP) monsoon break is investigated by analyzing the subseasonal evolution of TCs and corresponding circulations, based on 65 years of data from 1950 to 2014. The monsoon break has been identified as occurring over the WNP in early August. The present results show that TC occurrence decreases (increases) remarkably to the east of the Mariana Islands (southeast of Japan) during the monsoon break, which is closely related to local anomalous midtropospheric downward (upward) motion and lower-tropospheric anticyclonic (cyclonic) circulation, in comparison with the previous and subsequent convective periods in late July and mid-August. These changes of TC activity and the corresponding circulation during the monsoon break are more significant in typical monsoon break years when the monsoon break phenomenon is predominant. The reverse changes of TC activity to the east of the Mariana Islands and to the southeast of Japan during the monsoon break are closely associated with the out-of-phase subseasonal evolutions over these two regions from late July to mid-August, which are both contributed to greatly by 10–25-day oscillations. Finally, the roles of midlatitude and tropical disturbances on 10–25-day oscillations are also discussed.

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