# Ice Production in Ross Ice Shelf Polynyas during 2017-2018 from Sentinel-1 SAR Images
## 1 Introduction  
Coastal polynyas are common features during autumn and winter in polar regions and are dominantly caused by katabatic winds [1; 2; 3; 4]. The ice forming in coastal polynyas due to low air/water temperature and the consequent brine rejection increases the salinity of the near-surface layer water [5; 6; 7]. As the next wind blows away the just formed new ice in polynyas, a subsequent set of new ice forms, leading to further brine rejection. This process of new ice formation occurs frequently as long as the katabatic wind occurs frequently in polar regions. Coastal polynyas are therefore regarded as the factories of sea ice production (SIP) [8; 9; 10]. This high SIP in polar regions causes high-salinity water; the sinking of this dense water drives the global thermohaline circulation [11; 12; 13; 14; 15] and also impacts the bio-related material cycle and ecosystem [16; 17]. Many studies have been performed to quantitatively estimate polynya extent (area) and polynya ice production in coastal polynyas [18; 19; 20; 21; 22; 23; 24; 25; 26] and to analyze the relationship between sea ice production anddense deep-water formation [27; 28]. Among them, [PERSON] et al. first mapped the SIP in the Southern Ocean [8], and then [PERSON] and [PERSON] mapped SIP over the Arctic Ocean [23]. They reported that the highest ice production occurs in the RISP region with a mean annual cumulative SIP of \(390\pm 59\) km\({}^{3}\) from the 1990s to 2000s. This is consistent with the fact that Antarctic Bottom Water (AABW) with the highest salinity is formed in the Ross Sea [13]. In the Ross Sea, the development and variability of polynyas are primarily caused by southerly airflow and associated katabatic winds from the Ross Ice Shelf and the higher elevation of the Antarctic continent [3; 4]. It was reported that approximately 60% of the polynya events are linked to katabatic wind events; the remaining 40% are due to katabatic drainage winds and barrier winds that flow northward along the Transantarctic Mountains [2]. A summary of previous estimates of time-series of coastal polynya ice production in the Ross Sea is provided in Table 1. There are typically three polynyas in the Ross Sea: RISP, McMurdo Sound polynya (MSP), and Terra Nova Bay polynya (TNBP). Among previous studies, some regarded the RISP and MSP as one single polynya as Ross Sea Polynya (RSP), analyzing their combined ice production. The ice productions estimated by these studies show different results in the RSP. The long-term RSP ice productions (in Table 1) were all estimated based on the satellite passive microwave remote sensing (PMW) data and heat flux model. PMW data was used to derive ice thickness (of thin ice) and ice concentration and the heat flux model was used to calculate ice production based on the thin ice area (ice thickness \(<\)20 cm or sea ice concentration \(<\)75%). PMW is independent of sunlight, thus it is not affected by polar nights. Due to the strong penetrability of microwaves, PMW radiation can penetrate through the cloud cover. Therefore, the PMW data are available year-round at all weather conditions with a repeat cycle of half a day, and it is currently the longest dataset. The time series of satellite PMW data began in 1978, including the Scanning Multichannel Microwave Radiometer (SMMR, 1978-1987), the Special Sensor Microwave/Imager (SSM/I, 1987-2008), the Special Sensor Microwave Imager/Sounder (SSMI/S, 2007- ), and the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) and AMSR2 (2002- ). The frequencies of these sensors are different but they all include K and Ka bands which have been used for ice thickness derivation. Due to power constraints, the SMMR was operated every second day; thus, real repeat time of SMMR was longer than that of SSM/I, SSMI/S, and AMSR-E. Therefore, after 1987 when the SSM/I(s) on DMSP satellite series began service, the temporal resolution of PMW data improved.