Rapid and Sudden Advection of Warm and Dry Air in the Mediterranean Basin

Manuscript prepared for Nat. Hazards Earth Syst. Sci. with version 5.0 of the LATEX class copernicus.cls. Date: 20 November 2013 Rapid and sudden advection of warm and dry air in the Mediterranean basin J. Mazon1, D. Pino1,2, and M. Barriendos3 1Applied Physics Department, BarcelonaTech (UPC), Barcelona, Spain 2Institute for Space Studies of Catalonia (IEEC–UPC), Barcelona, Spain. 3Institut Catala` de Ciencies` del Clima (IC3) Correspondence to: J. Mazon ([email protected]) Abstract. Rapid advection of extremely warm and dry air normally and uncomfortably hot and usually humid weather, is studied during two events in the Mediterranean basin. On which should last at least one day, but conventionally it lasts 27 August 2010 a rapid advection of extremely warm and 35 from several days to several weeks. The definition presents dry air affected the northeast Iberian Peninsula during few slight variations in the values of exceeded temperature with 5 hours. At the Barcelona city center, the temperature reached respect to the average temperature depending on the national 39.3◦C, which is the maximum temperature value recorded weather service. However, a common characteristic is found during 230 years of daily data series. On 23 March 2008 a in all regional definitions: speaking about a heat wave re- rapid increase of temperature and drop of relative humidity 40 quires duration of at least 2 consecutive days of abnormal were recorded for few hours in Heraklion (Crete). During the temperature values. Thus, heat waves are considered a synop- ◦ 10 morning on that day the recorded temperature reached 34 C tic phenomenon that cover several thousands of square kilo- for several hours in the north coastline of this island. meters and last at least 2 or more days. According to the World Meteorological Organization none Many authors have studied the dynamics of heat waves and of these events can be classified as a heat wave, which re- 45 their effects in several fields, such as agriculture (Jolly et al., quires at least two days of abnormally high temperatures; 2005), human health (Smoyer-Tomic et al., 2003; Meehl and 15 or as a heat burst as defined by the American Meteorolog- Tebald, 2004), or discomfort (Matzarakis and Nastos, 2010; ical Society, where abnormal temperatures take place during Nastos and Matzarakis, 2012), tourism (Steadman, 1984; few minutes. For this reason, we suggest naming this type of Hamilton et al., 2005; Lise and Tol, 2002), energy consump- event flash heat. 50 tion (Karl and Quayle, 1981; Hassid et al., 2000) and wa- By using data from automatic weather stations in the ter demand (Smoyer-Tomic et al., 2003). Furthermore, some 20 Barcelona and Heraklion area and WRF mesoscale numer- studies (Meehl and Tebald, 2004; Trenberth et al., 2007) ical simulations, these events are analyzed. Additionally, the show that an increase in intensity, frequency and the dura- primary risks and possible impacts on several fields are pre- tion of heat waves around the Earth will occur during the th sented. 55 XXI century. In all scenarios shown in the 4 IPCC report (Trenberth et al., 2007), the Mediterranean basin will be one of the most significant regions affected by an increase in both the intensity and frequency of heat waves during this century. 25 1 Introduction If a smaller scale is considered, the glossary of AMET- 60 SOC defines a heat burst as a rare atmospheric event char- The World Meteorological Organization (WMO) defines a acterized by gusty winds, rapid temperature increase, and a heat wave as a phenomenon in which the daily maximum decrease in relative humidity, typically occurring at night or temperature of more than five consecutive days exceeds the early morning (Johnson, 1976; Glickman, 2000). It’s usually average maximum temperature by 5◦C with respect to the associated with descending air during a thunderstorm. The 30 period 1961–1990 (Frich et al., 2012). The glossary of me- 65 typical time scale of heat burst is few minutes, less than an teorology of the American Meteorological Society (AMET- hour. Recorded temperatures during heat bursts have reached SOC, Glickman (2000)) defines a heat wave as a period of ab- 2 J. Mazon et al.: Flash–heat events in the Mediterranean basin well above 32◦C, sometimes rising by 11◦C or more within midity. Automatic weather station located in the Barcelona ◦ only a few minutes. 120 city center recorded 39.3 C (the highest temperature since This paper aims to study two events associated with an 1780) and the relative humidity dropped to 19%. In addition, 70 increase in temperature and decrease in relative humidity oc- the recorded temperature values from 11:00 to 16:00 UTC curring at intermediate temporal and spatial scales. We will were above 30◦C, higher than 5◦C than the mean maximum call this phenomenon flash heat, because it occurs within temperature in August during the period 1961–1990, that has ◦ a time scale shorter than a heat wave but longer than a 125 been 26.8 C. However, for the 12 hours prior to and later heat burst. This event is usually associated with an adia- than the hours in which the maximum value was recorded, 75 batic warming of downslope winds, associated to Foehn ef- the temperature remained within normal values. As it will fect (Maninns and Sawford, 1979; Egger and Hoinka, 1992; be shown, the period of abnormally high temperature could Wakonigg, 1990). To our knowledge, there is no previous sci- be considered as occurring from 11:00 to 16:00 UTC. This entific reference naming this type of events. 130 event cannot be classified according to the above definitions Table 1 summarizes the differences between the three either as a heat wave or as a heat burst. 80 types of abnormal high temperature events mentioned above. Note the different spatial and temporal scales of flash heat, 2.1 Synoptic situation as well as the dynamics of its formation. The structure of this paper is as follows. Section 2 is de- Figure 1 shows the temperature at 850 hPa obtained by the voted to analyze and describe, by using observations and reanalysis of the National Centers of Environmental Predic- 85 mesoscale model numerical simulations, the 27 August 2010 135 tion (NCEP) at 00:00 UTC from 26 to 28 August 2010. A event in the northeast of the Iberian Peninsula, where a very ridge from North Africa remained stationary in Northwest warm and dry air mass affected this area over 8 hours. It fo- Africa for a few days before the 25 August 2010, when it cuses on the Barcelona area, where the maximum daily tem- began to move to the north. On 25 August at 00:00 UTC perature in over 230 years was recorded. According to this (not shown), the 25◦C isotherm at 850 hPa was located at 90 analysis, a preliminary flash–heat definition is proposed in 140 the southern Iberian Peninsula and a large anticyclonic ridge order to analyze the existence of similar flash–heat events was located in Northwest Africa. At the northern third of the during the XIX century in the daily temperature series of Iberian Peninsula the 850–hPa isotherm was 15◦C at 00:00 Barcelona (1790–2012). The rapid increase of temperature UTC. On 26 August, the ridge moved to the north. At 850 and decrease of relative humidity occurred on 23 March 2008 hPa (see Fig. 1a), the 25◦C isotherm was in the central and 95 in Heraklion (Crete island) is analyzed in Section 3. In Sec- 145 southern Iberian Peninsula. On the 27, at 00:00 UTC (Fig. tion 4 we describe the main impacts that this event could pro- 1b), the ridge (25◦C–isotherm at 850 hPa) extended from duce on several fields, mainly in agriculture, energy demand, the southwest to the northeast of the Iberian Peninsula, and health and fires. Finally, in Section 5 the main conclusions moved rapidly to the southeast, displaced by a northeast ad- are presented. vection. On the 28 August, at 00:00 UTC (see Fig. 1c), the ◦ 150 border of the 25 C–isotherm at 850 hPa was displaced to the southeast of the Iberian Peninsula. The 15◦C–isotherm 100 2 The 27 August 2010 event (Barcelona event) at 850 hPa approximately followed the Pyrenees Mountains. On the 29 of August the northeast advection increased, with According the Agency of Spanish Meteorology (AEMET), a 10◦C–isotherm at 850 hPa at 00:00 UTC over the Pyrenees the summer of 2010 was the third warmest summer recorded 155 (not shown). Several storms formed in the northeast Pyrenees in the Iberian Peninsula. Particularly, August 2010 was the during those days. In the south and southeast of the Iberian fifth warmest month since 1971; its mean temperature was Peninsula, the heat wave continued, with temperatures be- ◦ ◦ ◦ 105 1.5 C higher than the average monthly temperature and it tween 20 C and 25 C at 850 hPa at the south and southeast was the third warmest month in this century. At the south until the 31 August 2010. and east of the Iberian Peninsula, maximum temperatures be- ◦ tween 40 and 44 C were recorded. Minimum early morning 160 2.2 Analysis of surface observations temperatures of between 23 and 26◦C were recorded by sev- 110 eral official AEMET weather stations during this period. To avoid heat–island effect, data from the weather station in- However, the heat wave does not affect the north and stalled at the Fabra Observatory, located 10km away from northeast Iberian Peninsula. The warm and dry air mass was the city center (420 masl) was selected.

Load more