Brief communication: The anomalous winter 2019 sea-ice conditions in McMurdo Sound, Antarctica

McMurdo Sound sea ice can generally be partitioned into two regimes: (1) a stable fast-ice cover, forming south of approximately 77.6∘ S around March–April and then breaking out the following January–February, and (2) a more dynamic region north of 77.6∘ S that the McMurdo Sound and Ross Sea polynyas regularly impact. In 2019, a stable fast-ice cover formed unusually late due to repeated break-out events. We analyse the 2019 sea-ice conditions and relate them to a modified storm index (MSI), a proxy for southerly wind events. We find there is a strong correlation between the timing of break-out events and several unusually large MSI events.

Dust Storm Index Anomaly for Sand-Dust Events Monitoring in Western Iran and its Association with the NDVI and LST Anomalies

Sand-dust events (SDE) are an increasing concern in many arid and semi-arid regions of the world, which have severely damaged air quality and human health in recent years. This study was conducted to monitor the SDE in western Iran using the dust storm index anomaly (DSIA) during 2000–2018. The spatiot-emporal change detection and statistical analysis were used to understand the impacts of normalized difference vegetation cover anomaly (NDVIA) and land surface temperature anomaly (LSTA) on the SDE activities. The area has suffered from the highest dust pollution in 2004, 2009, and 2012 (DSIA > + 40) while it experienced the lowest dust pollution in 2002 and 2017 (DSIA<-40). Approximately 48% of western Iran experienced decreasing changes and 52 % of the total area experienced increasing changes in dust pollution during 2010–2018 compared to the previous years. Incremental changes in NDVIA and LSTA were observed in 73.2% and 7.5% of the study area while their decreasing changes were observed in 26.8% and 92.5% of the total area, respectively. Spatially, regions affected by the increase in dust pollution are mainly distributed in the eastern and southern regions of the study area. Significant effects of changes in anomalies of both terrestrial parameters on DSIA were observed throughout the study period (R LSTA−DSIA = + 0.52; R NDVIA−DSIA= -0.41); P < 0.05). It was also found that spatial correlation between LSTA and DSIA as well as NDVIA and DSIA in many parts of the study area were significant at the 95% confidence level (). These findings can be useful for decision-makers to assess the risks of dust pollution and reduce its negative consequences in western Iran.

Monitoring DSI and Lancaster Indices for Study Dust and Sand Storm In Meteorological Mehrabad Station of Tehran

The first climatic factors affecting the phenomenon of dust and fine dust are collected, reconstructed, extended and completed in the form of DSI (Dust Storm Index) and Lancaster in Mehrabad meteorological station of Tehran was studied and analyzed. The results showed that in Mehrabad meteorological station in terms of temperature in 1992 the lowest value and in 1998, 2001, 2017 the highest value and in terms of humidity in 2017 the lowest amount of humidity and in 2000 the highest amount of humidity and in terms of rainfall in the year 2013 the lowest amount of precipitation and in 2019 the highest amount of precipitation and in terms of evaporation in 2009 the lowest amount of evaporation and in 1391 the highest amount of evaporation and finally in terms of number of dust days in 1998 the lowest number of days and in 2009 the highest number of days Dust has been recorded. Mehrabad station of Tehran in years showed DSI index, more than one number and Lancaster index, more than fifty number in most of the mentioned years, the values of temperature and evaporation are high and the values of precipitation and humidity are relatively low, which shows the direct relationship between the dust storm index (DSI index) and mobility index of sand dunes (Lancaster index) is almost too high and above the number, It is noteworthy that in most of the mentioned years, Meteorological factors and data have been at Mehrabad station in Tehran.

Northeast Atlantic storminess in centennial reanalyses

&lt;p&gt;Global atmospheric reanalyses are commonly applied for the validation of climate models, diagnostic studies, and driving higher resolution numerical models with the emphasis on assessing climate variability and long-term trends. Over recent years, longer reanalyses spanning a period of more than hundred years have become available. In this study, the variability and long-term trends of storm activity is assessed over the northeast Atlantic in modern centennial reanalysis datasets, namely ERA-20cm, ERA-20c, CERA-20c, and the 20CR-reanalysis suite with 20CRv3 being the most recent one. All reanalyses, except from ERA-20cm, assimilate surface pressure observations, whereby ERA-20C and CERA-20c additionally assimilate surface winds. For the assessment, the well-established storm index of higher annual percentiles of geostrophic wind speeds derived from pressure observations at sea level over a relatively densely monitored marine area is used.&lt;/p&gt;&lt;p&gt;The results indicate that the examined centennial reanalyses are not able to represent long-term trends of storm activity over the northeast Atlantic, particularly in the earlier years of the period examined when compared with the geostrophic wind index based on pressure observations. Moreover, the reanalyses show inconsistent long-term behaviour when compared with each other. Only in the latter half of the 20th century, the variability of reanalysed and observed storminess time series starts to agree with each other. Additionally, 20CRv3, the most recent centennial reanalysis examined, shows markedly improved results with increased uncertainty, albeit multidecadal storminess variability does not match observed values in earlier times before about 1920.&lt;/p&gt;&lt;p&gt;The behaviour shown by the centennial reanalyses are likely caused by the increasing number of assimilated observations, changes in the observational databases used, and the different underlying numerical model systems. Furthermore, the results derived from the ERA-20cm reanalysis that does not assimilate any pressure or wind observations suggests that the variability and uncertainty of storminess over the northeast Atlantic is high making it difficult to determine storm activity when numerical models are not bound by observations. The results of this study imply and reconfirm previous findings that the assessment of long-term storminess trends and variability in centennial reanalyses remains a rather delicate matter, at least for the northeast Atlantic region.&lt;/p&gt;

A century of geomagnetic storms, CMEs and HSS/SIRs

&lt;p&gt;Geomagnetic storms are mainly driven by the two main solar wind transients: coronal mass ejections (CME) and high-speed solar wind streams with related (corotating) stream interaction regions (HSS/SIR). CMEs are produced by new magnetic flux emerging on solar surface as active regions, and their occurrence follows the occurrence of sunspots quite closely. HSSs are produced by coronal holes, whose occurrence at the ecliptic is maximized in the declining phase of the solar cycle.&lt;/p&gt;&lt;p&gt;Geomagnetic storms are defined and quantified by the Dst index that measures the intensity of the ring current and is available since 1957. We have corrected some early errors in the Dst index and extended its time interval from 1932 onwards using the same stations as the Dst index (CTO preceding HER). This extended storm index is called the Dxt index. We have also constructed Dxt3 and Dxt2 indices from three/two of the longest-operating Dst stations to extend the storm index back to 1903, covering more than a century of storms.&lt;/p&gt;&lt;p&gt;We divide the storms into four intensity categories (weak, moderate, intense and major), and use the classification of solar wind by Richardson et al. into CME, HSS/SIR and slow wind -related flows in order to study the drivers of storms of each intensity category since 1964. We also correct and use the list of sudden storm commencements (SSC) collected by Father P. Mayaud, and divide the storms of each category into SSC-related storms and non-SSC storms.&lt;/p&gt;&lt;p&gt;Studying geomagnetic storms of different intensity category and SSC relation allows us to study the occurrence of CMEs and HSS/SIR over the last century. We also use these results to derive new information on the centennial evolution of the structure of solar magnetic fields.&lt;/p&gt;

North Atlantic winter storm activity in modern reanalyses and pressure-based observations

This study analyzes changes in extratropical windstorms over the North Atlantic during the last decades. We assessed and compared North Atlantic winter storm activity in a comprehensive approach from three different data sources: modern reanalysis data sets, a dynamically downscaled high-resolution global atmospheric climate simulation, and observations. The multi-decadal observations comprise both a storm index derived from geostrophic wind speed triangles and an observational record of low pressure systems counted from weather analyses. Both observational data sets have neither been compared to the most recent reanalyses nor to the downscaled global climate simulation with respect to North Atlantic winter storms before.The similarity of the geostrophic wind speed storm index to reanalyzed high wind speed percentiles and storm numbers confirms its suitability to describe storm frequencies and intensities for multi-decadal time scales. The results show that high wind speeds, storm numbers, and spatial storm track distributions are generally alike in high-resolution reanalyses and downscaled data sets and they reveal an increasing similarity to observations over time. Strong decadal and multi-decadal variability emerged in high wind speed percentiles and storm frequency, but no long-term changes for the last decades were detected.