Characterization of Ice‐Nucleating Particles Over Northern India

Abstract

The sources and concentrations of ice‐nucleating particles (INPs) over India are not well known. Here, INP concentrations in rainwater from Northern India and a dust sample from the Thar Desert are characterized. Rainwater INP concentrations ranged between 104 and 3 × 107 L−1 water, spanning temperatures between −4 and −28 °C. During the monsoon season, INP concentrations were low and approached those in remote marine air mass. During the winter season, INPs active between −4 to −10 °C were occasionally observed. An increase in INP activity sometimes occurred after the initial onset of rain. The onset freezing temperature of samples active at warmer temperatures was shifted to colder temperature after heat treatment, suggesting that the INP activity stemmed from biological influence. Plating was used to isolate and sequence INP active bacterial strains from some of the rainwater samples, specifically strains of close taxonomic affiliation with the ice nucleating genera Pantoea. The size‐resolved ice nucleation active site density for 200–600‐nm particles of Thar Desert Dust ranged between 107 and 109 m−2 at −20 °C, values similar to dusts from other regions of the world. The data reported herein may help constrain models that seek to predict the impact of INP on the properties of mixed‐phased clouds over the Indian subcontinent.

The UNAM-droplet freezing assay: An evaluation of the ice nucleating capacity of the sea-surface microlayer and surface mixed layer in tropical and subpolar waters (edited by Dr. Michel Grutter)

“…As shown in Figure 5a, the homogeneous freezing curve obtained with the UNAM-DFA is close to the one reported by Tobo et al (2016). However, the liquid droplets from the present results were found to freeze at lower temperatures than those found in previous studies (e.g., Whale et al, 2015;Irish et al, 2017;Yadav et al, 2019). The variability between the homogeneous freezing curves shown in Figure 5a is not surprising given that the spontaneous freezing of liquid droplets is influenced by its size, the cooling rate, and the details of the method used (i.e., suspended droplets vs. droplets placed on cold stages), among other factors.…”

“…Figure 5b shows the relationship between INP concentration (in the form of ATD particles) and freezing temperature. Although the INP concentrations in our samples were lower than those observed by Yadav et al (2019), the trend with freezing temperature in both data sets is consistent.…”

“…where Nf is the number of frozen droplets at a specific temperature and N the total droplets of the ELISA plate (i.e., 96). The cumulative INP concentration (L -1 ) is derived following Equation 3 (Yadav et al, 2019):…”

“…Arizona Test Dust (ATD) was utilized in a secondary experiment to further assess the performance of the UNAM-DFA. ATD can be considered a proxy for natural mineral dust and its ice nucleating abilities in different ice nucleation modes are well known (Kanji et al, 2008;Kanji and Abbatt, 2010;Welti et al, 2009;DeMott et al, 2011;Niemand et al, 2012;Hader et al, 2014;Steinke et al, 2015;Yadav et al, 2019). An aqueous solution of 0.1% w/w ATD (ISO 12103-1; Powder Technology, Inc; A1 ultrafine) in MilliQ water was prepared and analyzed in the UNAM-DFA.…”

A diagnostic study of cloud physics and lightning flash rates in a severe pre‐monsoon thunderstorm over northeast India

“…During the winter season over north India, Yadav et al . () found ice nucleating particles likely to be biologically active between −4 to −10 °C. It is to be noted that NEI consists of hilly terrain with dense forest cover, also considered as a biodiversity hot spot of the world.…”