Modulation of Polar Low Activity by the Madden‐Julian Oscillation

Abstract

Polar lows (PLs) are intense mesoscale cyclones that form over high-latitude oceans (Rasmussen and Turner, 2003). They are characterized by intense surface winds and can produce heavy precipitation, strong icing, low visibility, and large ocean waves (Harrold & Browning, 1969;Orimolade et al., 2016;Samuelsen et al., 2015), posing hazards to high-latitude coastal communities and marine operations. However, it is challenging for global models to realistically represent or skillfully predict PLs due to their small scale (with a typical diameter of 200-500 km), short lifetime (typically <48 hr), and convective nature (e.g.

Polar low research: recent developments and promising courses of research

“…Indeed, the spiraliform cloud signature of some PLs could be due to a warm seclusion process (Stoll et al, 2021;Lackner et al, 2023). Thus, strong baroclinicity in addition to low static stability are key ingredients for PL development (Boyd et al, 2022;Wang et al, 2023). There are other factors that contribute to PL development, such as the generation of convergence zones when MCAOs occur downstream of a sea ice edge with a certain shape (Watanabe et al, 2022), and the occurrence of weather events that can trigger PL formation, such as katabatic storms (e.g., Gutjahr et al, 2022).…”

Subseasonal Predictions of Polar Low Activity Using a Hybrid Statistical‐Dynamical Approach

“…On the other hand, strong impacts of the MJO on PL activity do not always translate into enhanced prediction skill. An example is found over the Irminger Sea during phases 2–4 at week‐1 and week‐2 forecast range, where strong PL genesis frequency anomalies are represented by the PGI derived from the ERA5 (Figures 1n and 4n in Wang et al., 2023), suggesting that the WPM is sometimes unable to capture the extratropical impacts of the MJO on the regional climate conditions, which leads to poor PL prediction. It is important to note that our limited sample size may introduce sample fluctuations, so the influence of the MJO on PL prediction skill could be worth revisiting on a larger scale in future studies.…”

“…Lin, 2020). Wang et al (2023) recently found that the MJO has strong impacts on PL activity across the sub-Arctic through the modulation of regional environmental conditions, and the PGI was able to skillfully represent these impacts. In the following paragraph, we will briefly explore how the MJO influences PL prediction skill.…”

“…These particular examples are associated with strong PL genesis frequency anomalies (see Fig. 1 in Wang et al., 2023), illustrating the predictable influences of the MJO on PL activity. Beyond the week‐1 forecast range, significant large HSS values can be found over various regions depending on MJO phase, such as during phase 2 over the Bering Sea or during phase 1 over the Sea of Japan, where the HSS varies from 70% to over 90%.…”

“…On the other hand, PL predictability on the subseasonal time scale is yet to be studied, and subseasonal forecasts of PL activity are seldom issued, if at all. The subseasonal variability of PL activity has received some attention and been linked to certain modes of climate variability, including the Madden‐Julian Oscillation (MJO; Wang et al., 2023), North Atlantic Oscillation (NAO; Claud et al., 2007; Mallet et al., 2013), Arctic Oscillation (AO; Boyd et al., 2022), and the Pacific North‐American pattern (PNA; Chen & von Storch, 2013; Boyd et al., 2022), through the impacts of large‐scale environmental conditions. These modes could serve as a source of subseasonal predictability for PL activity (or statistics of PLs, in contrast to individual PLs) and facilitate extended‐range forecasts.…”