Impact of ice nuclei on the development of cumulus clouds over North China Plain
： 2018 - 09 - 09
： 2018 - 04 - 27
： 2018 - 09 - 11
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Abstract & Keywords
Abstract: Background, aim and scope: In the present study, the effect of ice nuclei (IN) on the development of cumulus clouds over the North China Plain has been investigated. A convective cumulus cloud event occurring on 24 August 2014 is simulated, and the sounding profile reveal a moderate instability with a convective available potential energy (CAPE) of 651 J kg-1. Materials and Methods: By using a Cloud-Resolving Weather Research and Forecasting (CR-WRF) model with a two-moment bulk microphysical scheme, this study provides a comprehensive view of the response of cloud microphysics to the IN. The HCCN represents the polluted conditions with the CCN of 9000 cm-1; the MCCN represents the clean conditions with CCN of 900 cm-1; the LCCN represents the background conditions with the CCN of 90 cm-1. A set of black carbon (BC) profiles is used in the simulations, with the surface number concentration varying from 2 to 2000 cm-3 and the mass concentration varying from 0.006 to 5.6 µg cm-3. Results: The simulation results show that in the LCCN condition, the ice number concentration is higher than the other two cases (HCCN and MCCN) when BC number concentration is very low; Under the HCCN condition，the ice number concentration increases with the increases of BC more sharply than in the LCCN cases. Besides, increasing IN concentrations slightly enhances the cloud core updraft and intensifies the convection under various CCN situations. The precipitation enhancement is less than 1% with the IN concentration increasing from 0.006 to 5.6 µg cm-3. Discussion: Ice, snow and graupel number concentrations increase with the increases of BC. The core updraft of the cloud intensified with the increases of BC, because the more condensation and sublimation processes the more latent heat can be released, it can be further heated the atmosphere. Besides, the enhancement of the core updraft inhibits the core downdraft, and the precipitation is decreased in the whole processes. Conclusions: IN plays an important role in the formation of the ice crystals. The precipitation increases steadily with the increases of BC concentrations, caused by the enhanced mix-phased process due to increasing BC, but it is not sensitive to the BC variation. The IN generally do not play a dominant role in the development of cumulus clouds during summertime. Recommendations and perspectives: (1) The dust and other organic aerosol that also act as IN were not considered in this simulation study. (2) The formation of ice crystals was not considered completely because of the complex processes of them. (3) The further research can also try to simulate the response of cloud microphysical processes to the IN in different regions such as over the sea area.
Keywords: CR-WRF model; ice nuclei; cumulus clouds; North China Plain
20世纪50年代末，Ludlam and Mason（1958）指出IN在云和降水的发生和发展中起着重要作用，此后IN对云和降水的影响受到了很多研究人员的重视（Pruppacher and Klett，1978；Van et al，2006；Yang et al，2011）。研究指出：在沙尘天气下，沙尘气溶胶作为IN，通过改变对流层高层冰晶的分布影响区域降水的分布（Huang et al，2006）。大量的研究进一步表明，IN是混合云发展的主要因素，是降水发生的初步条件（Choi et al，2010；Findeisen，1938；Hoose and Möhler，2012；Koop et al，2000；Phillips et al，2008；Blyth et al，2010；Storelvmo et al，2011）。IN浓度的改变对冰晶浓度及冰晶尺度都有影响，IN数浓度增加会导致云中过冷水滴增多，冰晶粒子相应的增加；同时会使水成物粒子有效半径减小，使得雪晶和霰粒子的量减小；IN的增加也会导致释放潜热加强云内对流，从而产生更多的降水（Gierens，2003；Isaac and Douglas，2010；Jensen et al，2001；Li et al，2008b；Zhou et al，2017）。然而，IN对云和降水的影响不仅与其自身的物理化学特征有关，还与地理空间等因素相关。另外，由于人类的活动不断的产生新的IN排放到大气环境中，IN对不同区域天气气候背景下的云和降水的影响表现出显著的局地性。因此，分区域讨论IN对云形成和发展的研究显得尤为必要。

1 模式、数据处理与方法
1.1 模式的基本预报方程

$${\mathrm{N}}_{\mathrm{x}}\left(\mathrm{D}\right)={\mathrm{N}}_{0\mathrm{x}}{\mathrm{D}}_{\mathrm{x}}^{{\mathrm{\alpha }}_{\mathrm{x}}}\mathrm{exp}\left(-{\mathrm{\lambda }}_{\mathrm{x}}{\mathrm{D}}_{\mathrm{x}}\right) \left(1\right)$$

$${\mathrm{V}}_{\mathrm{x}}\left({\mathrm{D}}_{\mathrm{x}}\right)={\mathrm{A}}_{\mathrm{v}\mathrm{x}}{\mathrm{D}}_{\mathrm{x}}^{{\mathrm{B}}_{\mathrm{v}\mathrm{x}}} \left(3\right)$$

1.2 模式的微物理过程

1.3 气溶胶粒子的粒径分布

Fig.1 Atmospheric sounding over North China Plain (114°21'E, 37°10′12″N, 181 m a.s.l.) at 08:00 UTC on 24 August 2014

2 结果分析

2.1 冰晶、雪晶和霰粒子对IN的响应

Fig.2 Modeled P-mean of ice number concentration as a function of the initial IN and CCN in Cu-NCP

Fig.3 Modeled P-mean of snow number concentration as a function of the initial IN and CCN in Cu-NCP

Fig.4 Modeled P-mean of graupel number concentration as a function of the initial IN and CCN in Cu-NCP.

Under background ($$20{\mathrm{c}\mathrm{m}}^{-3}$$, blue), clean (200 $${\mathrm{c}\mathrm{m}}^{-3}$$, green), and polluted (2000 $${\mathrm{c}\mathrm{m}}^{-3}$$, red) (IN); under HCCN case (a1, b1), MCCN case (a2, b2), and LCCN case (a3, b3) for ice particles (ice + snow) (from a1 to a3), and graupel (from b1 to b3) in Cu-NCP, respectively.

Fig.5 Vertical profiles of time-averaged masses of hydrometeors

2.2 云滴粒子和云水含量对IN的响应

Fig.6 Modeled P-mean of cloud droplet number concentration (a) and effective radius (b) as a function of the initial IN and CCN in Cu-NCP

Fig.7 Modeled P-mean of cloud water mass concentration (a) and supercooled cloud water mass concentration (b) as a function of the initial BC in the Cu-NCP
2.3 云内对流强度对IN的响应

Fig.8 Modeled P-mean of updraft (a) and downdraft (b) in the core area (defined as an area where the absolute vertical of wind is greater than 1 〖m s〗^(-1) and the total condensed water content exceeds 10^(-2) g kg^(-1)) as a function of the initial IN and CCN in Cu-NCP

Fig.9 Modeled P-mean of maximum updraft (a) and maximum downdraft (b) as a function of the initial BC in the Cu-NCP
2.4 降水对IN的响应

Fig.10 Modeled cumulative precipitation inside the model domain (mm) as a function of the initial IN and CCN in Cu-NCP
3   结论

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