Influence of the previous North Atlantic Oscillation (NAO) on the spring dust aerosols over North China
Abstract. The North Atlantic Oscillation (NAO) has been confirmed to be closely related to the weather-climate in many regions of the Northern Hemisphere, however, its effect and mechanism upon the formation of regional dust events (DEs) have rarely been involved in China. By using the station observation data, and multi reanalysis datasets, the influence of NAO on the dust aerosols (DAs) in China, as well as the corresponding mechanism of synoptic cause are explored in perspective of transient eddy fluxes. It is found that the DAs in the non-dust source areas show high values with a strong annual variability in north of the Yangtze River (30–40° N, 105–120° E), which is referred to as the North China hereafter. A significant negative relationship is indicated between the boreal winter NAO index and the late spring DAs in the North China with the correlation coefficient of −0.39. According to the 9 spring DEs affected significantly by negative phase of the preceding winter NAO in the North China during 1980–2020, it is shown that before the outbreak of DEs, due to the transient eddy momentum (heat) convergence (divergence) over the dust aerosol (DA) source regions, the zonal wind speed increases in upper-level troposphere, strengthening the zonal wind in the middle-lower levels through momentum downward transmission. Simultaneously, there is transient eddy momentum (heat) divergence (convergence) around the Ural Mountains, which is favorable for establishment and maintenance of the Ural ridge, as well as development of the air temperature and vorticity advections. The combined action of temperature and vorticity advections results in the Siberian Highs and Mongolian cyclone to establish, strengthen, and move southward near the surface, guiding the cold air from high latitudes southward, and is favorable to the uplift and transmission of DAs to the downstream North China. After the outbreak of DEs, change of transient eddy fluxes in the DA source regions and the Urals regions, leads to both energy and mass divergence and reduction of the zonal winds over the North China. Accompanying with the prevailing southerly airflow in south of the North China, a stable high value of DA concentration is maintained for 1–2 days. This study reveals the impact of transient eddy fluxes transport on the dusty weather anomalies modulated by the NAO negative signal in the North China, which can deepen the understanding of formation mechanism of DEs in China.
Yan Li et al.
Status: open (until 28 Mar 2023)
- RC1: 'Comment on egusphere-2023-52', Anonymous Referee #1, 08 Mar 2023 reply
- RC2: 'Comment on egusphere-2023-52', Anonymous Referee #2, 11 Mar 2023 reply
- RC3: 'Comment on egusphere-2023-52', Anonymous Referee #3, 11 Mar 2023 reply
Yan Li et al.
Yan Li et al.
Viewed (geographical distribution)
Using the station observations and multi reanalysis data, the authors investigated the possible influences of the previous NAO on the dust aerosols over northern China. Authors concluded that the boreal winter NAO has significant impacts on the following spring dust aerosols, particularly during the negative phase of the NAO. The thermal and dynamical processes relevant to the anomalous NAO on the circulation are analyzed, and it indicated that the impact of transient eddy fluxes transport plays important role in the formation of the dust aerosol events. I agree with the authors that the influence of previous NAO on dust aerosols in China cannot be ignored. And it is an important interdisciplinary issue that needs more attention and deep research. Overall the manuscript is well written and clear, and the figures are also appropriate and clear. However, there are some problems with this manuscript, and it cannot be accepted by ACP as it is now. Some specific comments or suggestions are listed as follows:
(1) Introduction: the review of the dust aerosol’s climate effect and the NAO’s impacts on the regional climate anomalies are a little repetitive and lengthy. Address and summary the major research progress of the present work.
(2) NAO index: There are lots of definitions of the NAOI, what is the advantage of the NAOI used, and whether the result is robust if other definitions are used. The authors need to further compare the different NAOI, and clarify whether the result is subject to the NAOI.
(3) The role of previous winter NAO on the following spring dust aerosols is discussed, however, as reported ENSO shows a significant role in determining the winter and spring climate anomalies over eastern China. it is of interest to further discuss whether the impacts of NAO on the aerosols are independent of ENSO.
(4) L218: prior to rather than previous to
(5) Line 34: The descriptions are confusing.
(6) In the upper troposphere, it is emphasized that both the jet stream and downward transmission of high-altitude wind speed momentum contribute to the formation of the dust aerosols, however, without a detailed physical explanation of the combined role the two.
(7) In the middle troposphere, the evolution of the trough-ridge system along with the occurrence of the dust aerosol events should be further analyzed. The involved physical process, particularly, which variable is more important in the process warranty further illustration.
(8) There are lots of clerical errors, i.e.,
L306, should be 0.1 in and 0.2 in
L351, should be 35°-50°N, 70°-110°E
L356-360, lengthy and repetition
L377, should be prior to
L404, should be 30°-60°N, 105°-130°E
The authors should carefully check the whole manuscript.
(9) Figures 2, 4, 7, 10, 13, without clarification of the axis, Figure 3, without units.