Characteristics of High‐Precipitation Events in Dronning Maud Land, Antarctica E

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 115, D14107, doi:10.1029/2009JD013410, 2010 Click Here for Full Article Characteristics of high‐precipitation events in Dronning Maud Land, Antarctica E. Schlosser,1 K. W. Manning,2 J. G. Powers,2 M. G. Duda,2 G. Birnbaum,3 and K. Fujita4 Received 19 October 2009; revised 28 January 2010; accepted 26 February 2010; published 21 July 2010. [1] High‐resolution Antarctic Mesoscale Prediction System archive data were used to investigate high‐precipitation events at the deep ice core drilling site Kohnen Station, Dronning Maud Land, Antarctica, during the period 2001–2006. The precipitation is found to be highly episodic, with, on average, approximately eight high‐precipitation events per year that can bring more than half of the total annual accumulation. The duration of the events varies between 1 day and about 1 week. On most days in the remaining time of the year, however, daily precipitation sums are about one order of magnitude smaller than that for the high‐precipitation events. Synoptic weather patterns causing these events were directly connected to frontal systems of cyclones in only 20% of the 51 investigated cases. The majority of the events occurred in connection with (blocking) anticyclones and correspondingly amplified Rossby waves, which lead to advection of warm, moist air from relatively low latitudes. Possible changes in the seasonality and frequency of these events in a different climate can lead to a bias in ice core properties and might also strongly influence the mass balance of the Antarctic continent and thus global sea level change. Citation: Schlosser, E., K. W. Manning, J. G. Powers, M. G. Duda, G. Birnbaum, and K. Fujita (2010), Characteristics of high‐ precipitation events in Dronning Maud Land, Antarctica, J. Geophys. Res., 115, D14107, doi:10.1029/2009JD013410. 1. Introduction Antarctica (EPICA), at Kohnen Station [75.00°S, 0.50°E, 2892 m above sea level (asl)] [Oerter et al., 2004], and one [2] Even with modern techniques, measuring Antarctic at Dome Fuji (77.32°S, 39.7°E, 3810 m asl) [Horiuchi et al., precipitation is a challenging task because of the remoteness 2008]. Both cores reached bedrock and, together with the and cold of the continent combined with the aridity of the second core drilled within EPICA, Dome C, yielded infor- interior and the prevailing strong winds in coastal areas that mation about the climate of the past 800 kyr [European make it difficult to distinguish between real precipitation and Project for Ice Coring in Antarctica (EPICA) Community blowing or drifting snow. However, a thorough knowledge Members, 2004]. Of special interest for ice core interpreta- of the Antarctic precipitation regime is important for the tion is the investigation of the occurrence of high precipi- following two reasons: (1) snowfall is the largest positive tation compared to diamond dust, also called “clear‐sky component of the Antarctic mass balance and its behavior in precipitation” (even though it also occurs under overcast a changing climate influences global sea level change, and conditions beneath a cloud layer; G. Birnbaum, personal (2) for a correct interpretation of ice cores (one of the most communication). Diamond dust, which is formed from in important information sources in paleoclimatology), knowl- situ nucleation of ice crystals in the extremely cold air [King edge about the seasonality of accumulation and possible and Turner, 1997], is assumed to show some seasonal changes in that seasonality during climatic change is a basic variations but basically occurs in each month. Episodically requirement. occurring, synoptically induced high‐precipitation events [3] In Dronning Maud Land (DML), in the Atlantic sector are rare in the interior of the continent, but a few events per of Antarctica, two deep ice cores were recently drilled: one year can bring a large percentage of the total annual pre- in the framework of the European Project for Ice Coring in cipitation. A possible tendency of those events to occur in certain seasons could lead to a strong bias in ice core 1Institute of Meteorology and Geophysics, University of Innsbruck, properties [Noone and Simmonds, 1998; Jouzel et al., 1997, Innsbruck, Austria. 2003; Schlosser, 1999], in particular in the stable isotope 2Mesoscale and Microscale Meteorology Division, Earth System Laboratory, National Center for Atmospheric Research, Boulder, ratio, which is used to derive paleotemperatures, but also in Colorado, USA. various chemical properties. A possible over‐representation 3Alfred‐Wegener Institute for Polar and Marine Research, of summer snow, for instance, would lead to a higher stable Bremerhaven, Germany. 4 isotope ratio and, thus, to a seemingly higher temperature, Graduate School of Environmental Studies, Department of even if the mean annual temperature had not changed at all. Hydrospheric‐Atmospheric Science, Nagoya University, Furo‐cho, Chikusa‐Ku, Nagoya, Japan. Therefore, a thorough understanding of precipitation pro- cesses is needed for a correct ice core interpretation. For Copyright 2010 by the American Geophysical Union. Kohnen Station, because it is a summer ice core drilling 0148‐0227/10/2009JD013410 D14107 1of14 D14107 SCHLOSSER ET AL.: HIGH‐PRECIPITATION EVENTS IN ANTARCTICA D14107 station, daily precipitation observations are available only eral synoptically induced precipitation events per year that for a restricted time period. However, model results show brought exceptionally high precipitation to the high Ant- for the majority of the time very small daily precipitation arctic plateau. Two case studies revealed that the high pre- sums. Unlike at Dome C or Dome Fuji, which are both cipitation amounts were caused by amplification of upper situated at higher altitudes and larger distances from the level planetary waves directing warm, moist air from lower coast than Kohnen Station, these small precipitation latitudes toward the interior of the continent. amounts are not necessarily attributed to diamond dust [9] These results were confirmed by Reijmer and Van den formation; they can also be attributed to a weak synoptic Broeke [2003], who found that accumulation at several influence. However, both types seem to be fairly evenly AWSs in DML occurred in many small and a few large distributed over the year and, thus, do not lead to a bias in precipitation events per year, with those few large events the ice core properties. accounting for up to 50% of the total annual accumulation. [4] Climate model simulations have shown a poleward Usually air temperature and wind speed increased consid- shift of Southern Hemispheric storm tracks in a warmer erably during the large events [Reijmer and Van den Broeke, climate, which means significant changes in the spatial 2001]. This had also been found by Noone and Simmonds precipitation distribution [Bengtsson et al., 2006]. This [1998], who used a general circulation model (GCM) to supports the hypothesis of systematic changes in cyclone investigate the synoptic patterns that cause unusually high behavior between glacial and interglacial time periods, precipitation in Antarctica. which must be considered for interpretation of ice core [10] At Kohnen Station, Birnbaum et al. [2006] investi- properties. gated the weather patterns that led to high precipitation [5] In this study, an investigation of “high‐precipitation amounts during several summer seasons. They studied a set events” at Kohnen Station, the EPICA drilling site in of visual observational data and the corresponding ECMWF western Dronning Maud Land, is presented. The study is operational analyses. For the summer they identified three based mainly on the high‐resolution Antarctic Mesoscale typical categories of weather situations that brought excep- Prediction System (AMPS) archive data, but it also draws tionally high snowfall: (1) occluding fronts from eastward on some temporally restricted observational data from moving low‐pressure systems, (2) large‐scale lifting pro- Kohnen Station [Birnbaum et al., 2006] and Dome Fuji cesses caused by an upper‐air low west of Kohnen Station, [Fujita and Abe, 2006]. Typical synoptic patterns connected and (3) retrograde lows or secondary lows with frontal to high‐precipitation events are classified, and their fre- systems. The second category, an upper air low west of the quency and seasonality is investigated. The corresponding base, leads to a northwesterly flow over DML that can be precipitation amounts are compared to estimated amounts fairly stable over several days in the case of a blocking during periods with diamond dust. An overview of previous anticyclone above eastern DML. Such blocking high‐ studies of Antarctic precipitation and the synoptics involved pressure systems were also studied by Enomoto et al. [1998] is given in section 2, and AMPS is described in section 3. In for Dome Fuji, where they observed an extreme winter section 4 the synoptic patterns for high‐precipitation events warming connected to a blocking high that persisted for are introduced and, in section 5, frequency distribution and several weeks and involved the aforementioned advection of seasonality of these events are discussed. After a short warm, moist air. Owing to the extremely high altitude of consideration of diamond dust (section 6), a summary and Dome Fuji (3810 m asl), the air is often not moist enough to conclusions are presented in section 7. produce precipitation, but the corresponding cloud cover changes the radiation conditions, namely the longwave

Load more