Beatriz M. Funatsu

Convective activity in Mato Grosso state (Brazil) from microwave satellite observations: Comparisons between AMSU and TRMM datasets

We present a characterization of convective activity at sub-regional scale from two sets of satellite-based microwave observations: the Advanced Microwave Sounding Unit (AMSU) and the combined Tropical Rainfall Measuring Mission (TRMM) microwave imager and precipitation radar data, for the period 2001 to 2011. We focus on the state of Mato Grosso, Brazil, located at the southern edge of the so-called Legal Amazon which has undergone intense land cover transformation in the last 4 decades. The annual cycle of mean convective activity described by AMSU and TRMM are in good agreement, with a correlation close to 0.80. The mean amplitude of convective activity is maximal early in the rainy season, except for AMSU deep convective area, which presents a maximum in January. The diurnal cycle of convection was examined for the period 2003 to 2007, and it was found that convection is maximal near 1500 local time (LT) and minimal around 0700 LT. Unlike the amplitude, the phase shows little intra-seasonal and interannual variability. A slight decrease in convective activity in the studied period was found possibly indicating an extension of the dry season. Comparisons of convective activity between deforested and forested areas showed no significant differences in the phase of the diurnal cycle, but our analysis shows a tendency for increase (decrease) in convection in deforested (forested) areas for the period considered. A longer time series is however necessary in order to strengthen the robustness of our results.

Comparison between the Large-Scale Environments of Moderate and Intense Precipitating Systems in the Mediterranean Region

A characterization of the large-scale environment associated with precipitating systems in the Mediterranean region, based mainly on NOAA-16 Advanced Microwave Sounding Unit (AMSU) observations from 2001 to 2007, is presented. Channels 5, 7, and 8 of AMSU-A are used to identify upper-level features, while a simple and tractable method, based on combinations of channels 3-5 of AMSU-B and insensitive to land-sea contrast, was used to identify precipitation. Rain occurrence is widespread over the Mediterranean in wintertime while reduced or short lived in the eastern part of the basin in summer. The location of convective precipitation shifts from mostly over land from April to August, to mostly over the sea from September to December. A composite analysis depicting large-scale conditions, for cases of either rain alone or extensive areas of deep convection, is performed for selected locations where the occurrence of intense rainfall was found to be important. In both cases, an upper-level trough is seen to the west of the target area, but for extreme rainfall the trough is narrower and has larger amplitude in all seasons. In general, these troughs are also deeper for extreme rainfall. Based on the European Centre for Medium-Range Weather Forecasts operational analyses, it was found that sea surface temperature anomalies composites for extreme rainfall are often about 1 K warmer, compared to nonconvective precipitation conditions, in the vicinity of the affected area, and the wind speed at 850 hPa is also stronger and usually coming from the sea.

Impact of land-cover change in the Southern Amazonia climate: a case study for the region of Alta Floresta, Mato Grosso, Brazil

The transformation of forest into pastures in the Brazilian Amazon leads to significant consequences to climate at local scale. In the region of Alta Floresta (Mato Grosso, Brazil), deforestation has been intense with over half the forests being cut since 1970. This article first examines the evolution of precipitation observed in this region and shows a significant trend in the decrease in total precipitation especially at the end of the dry season and at the beginning of the rainy season. The study then compares the temperatures measured in cleared and forested sectors within a reserve in the area of Alta Floresta (Mato Grosso, Brazil) between 2006 and 2007. The cleared sector was always hotter and drier (from 5% to 10%) than the forested area. This difference was not only especially marked during the day when it reached on average 2°C but also seemed to increase during the night with the onset of the dry season (+0.5°C). The Urban Heat Island effect is also evident especially during the night and in the dry season.

Rainfall patterns in the Southern Amazon: a chronological perspective (1971–2010)

The aim of this study is to characterize rainfall patterns in a vast transition zone between the Amazon and the Cerrado Biomes. The analysis is focused on annual and seasonal tendencies, mainly about the onset and offset of the rainy season, its length and shifts. More than 200 Rain Gauges (RGs) were analyzed in the study area using Pettitt’s and Mann-Kendall’s non-parametric tests allied to a Linear Regression Analysis over the period 1971–2010. The onset and offset dates of the rainy season and its duration are also identified for 89 RGs. Pettitt’s test indicates ruptures in 16xa0% of the rainfall time series while Mann-Kendall’s monthly test indicates that 45xa0% of the RGs had negative trends, mainly in the transition seasons (spring and austral autumn). Linear Regression Analysis indicates negative trends in 63xa0% of the time series concomitant to the rainy season onset and offset analysis, which confirmes a delay for the onset of the rainy season in 76xa0% of the RGs and a premature demise for 84xa0% of the RGs. Identification of the tendencies for rainy season duration indicates that the rainy season has become shorter at 88xa0% of the RGs. There were recurring patterns in the results displaying drier conditions in RGs localized in deforested areas opposed to forested locations.

Cross-validation of Advanced Microwave Sounding Unit and lidar for long-term upper-stratospheric temperature monitoring

A comparison between NOAA-16 Advanced Microwave Sounding Unit (AMSU) and lidar upper-stratospheric temperature measurements for the period from 2001 to 2007 for purposes of temperature monitoring is presented. Monthly means of lidar data from the Observatoire de Haute-Provence and AMSU data over Western Europe were found to have high correlation, particularly in winter months, when based on measurements for overlapping nights but lower correlation when different sets of days were used for the monthly mean calculation. This result implies that temperatures from lidar measurements are representative of an area relatively larger than its location, in a monthly mean timescale. However, the effect of temporal sampling arising from the fact that lidar measurements are only made in nights without visible cloud cover introduces discrepancies that propagate on the calculation of temperature tendencies. The estimated cooling rate based on lidar and AMSU data sets are in good agreement, although they are more negative than trends previously found based on the Stratospheric Sounding Unit data record from 1979 to 2005 for the middle-upper stratosphere. In addition, the effect of NOAA satellite drift was to produce a difference (between monthly means for day and night passes) of up to 3 K near the stratopause, which must be accounted for particularly when a longer time series will be available.

Projet Cyprim, partie I : Cyclogenèses et précipitations intenses en région méditerranéenne : origines et caractéristiques. - Cyclogenesis and heavy precipitations in the Mediterranean area: origins and characteristics.

Le premier volet du projet Cyprim vise a mieux identifier les precurseurs des cyclogeneses et des precipitations intenses en region mediterraneenne. Cet article en presente les principaux resultats. Il est question des ingredients meteorologiques a lorigine de ces systemes, de la grande a la mesoechelle, des causes des fortes intensites, localisations et parfois stationnarite des recipitations associees. Le coeur de larticle presente des methodes didentification des anomalies de tourbillon potentiel liees a loccurrence devenements precipitants intenses et dresse une climatologie de ces anomalies. Les perspectives dexploitation de cette information pour ameliorer la qualite des previsions sont evoquees. ENGLISH VERSION: The first part of the CYPRIM project (Cyclogenesis and intense precipitations in the Mediterranean region) aims at a better identification of the precursor structures of cyclogenesis and heavy precipitation in the Mediterranean region. This article presents the main results. It mentions the meteorological ingredients from which these systems originate from the large to themesoscale, the reasons for large intensities, the localization and sometimes stationarity of the associated precipitations. The heart of the article shows methods for identifiying potential vorticity anomalies involved in the occurrence of heavy precipitation events and sets up a climatology of these anomalies.The perspectives of the usefulness of this information for improving forecast quality are discussed.

Regional and seasonal stratospheric temperature trends in the last decade (2002–2014) from AMSU observations

Stratospheric temperature trends for the period 2002-2014 have been estimated using NOAAs Integrated Microwave Inter-Calibration Approach (IMICA) version of AMSU on AQUA satellite. In this period the stratosphere continued cooling over most of the globe with a rate ranging from -0.4±0.3 to -0.5±0.4 K/decade above 25 km. Considering specific latitude bands, trends are highly variable with height. In the Tropical region, trends vary from -0.5±0.3 K/decade for channel 12 (∼30 km) to -0.7±0.3 K/decade for higher channels, and present small seasonal variability in the intensity of cooling. In the polar regions and in the mid-latitudes, trends for all channels are negative but not significant; uncertainties are large due to the high dynamical variability particularly in high latitudes. There is also large seasonal variability, with Southern mid-latitudes seasonal trends significant during summer (DJF) and autumn (MAM) above ∼25 km, with values ranging from -1.0±0.5 to -0.6±0.5 K/decade. Regional trends estimated with AMSU and long-term lidar measurements (over 2 decades) confirm stratospheric cooling in the Northern mid-latitudes and Tropical regions. The effect of the length of the short series on trends was found to be small outside polar regions. It was found to be large in polar regions with about 1 K changes in trend depending on start dates of the time series.

Monitoring Rainfall Patterns in the Southern Amazon with PERSIANN-CDR Data: Long-Term Characteristics and Trends

Satellite-derived estimates of precipitation are essential to compensate for missing rainfall measurements in regions where the homogeneous and continuous monitoring of rainfall remains challenging due to low density rain gauge networks. The Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks—Climate Data Record (PERSIANN-CDR) is a relatively new product (released in 2013) but that contains data since 1983, thus enabling long-term rainfall analysis. In this work, we used three decades (1983–2014) of PERSIANN-CDR daily rainfall data to characterize precipitation patterns in the southern part of the Amazon basin, which has been drastically impacted in recent decades by anthropogenic activities that exacerbate the spatio-temporal variability of rainfall regimes. We computed metrics for the rainy season (onset date, demise date and duration) on a pixel-to-pixel basis for each year in the time series. We identified significant trends toward a shortening of the rainy season in the southern Amazon, mainly linked to earlier demise dates. This work thus contributes to monitoring possible signs of climate change in the region and to assessing uncertainties in rainfall trends and their potential impacts on human activities and natural ecosystems.

Postmillennium changes in stratospheric temperature consistently resolved by GPS radio occultation and AMSU observations

Temperature changes in the lower and middle stratosphere during 2001-2016 are evaluated using measurements from GPS Radio Occultation (RO) and Advanced Microwave Sounding Unit (AMSU) aboard the Aqua satellite. After downsampling of GPS-RO profiles according to the AMSU weighting functions, the spatially and seasonally resolved trends from the two data sets are in excellent agreement. The observations indicate that the middle stratosphere has cooled in the time period 2002-2016 at an average rate of –0.14±0.12 to –0.36±0.14 K/decade, while no significant change was found in the lower stratosphere. The meridionally and vertically resolved trends from high-resolution GPS-RO data exhibit a marked inter-hemispheric asymmetry and highlight a distinct boundary between tropospheric and stratospheric temperature change regimes matching the tropical thermal tropopause. The seasonal pattern of trend reveals significant opposite-sign structures at high and low latitudes, providing indication of seasonally varying change in stratospheric circulation.

Local rainfall trends and their perceptions by Amazonian communities

Climate change in the Amazon region is the subject of many studies not only due to its stance as an emblematic ecosystem but also as a region where changes have been dramatic for over 30 years, mainly due to deforestation. We investigate how people settled in the Amazon perceive environmental changes by comparing these perceptions with satellite rainfall data for 12 sites representing the community diversity in the region. Perceptions are varied and agreement with physical, measured data is not always good. However, the arc of deforestation, where the downward trend of rainfall is more strongly observed, also appears as the region where the populations have the highest perception of rainfall change.