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The data presented in this report are preliminary. Ranks and anomalies may change as more complete data are received and processed. The most current data may be accessed via the Global Surface Temperature Anomalies page.
Temperature anomalies for April 2009 are shown on the dot maps below. The dot map on the left provides a spatial representation of anomalies calculated from the Global Historical Climatology Network (GHCN) dataset of land surface stations using a 1961-1990 base period. The dot map on the right is a product of a merged land surface and sea surface temperature (SST) anomaly analysis developed by Smith and Reynolds (2005). Temperature anomalies with respect to the 1961-1990 average for land and ocean are analyzed separately and then merged to form the global analysis. Additional information on this product is available.
During April 2009, warmer-than-average temperatures were present across Mexico, the northeastern and western contiguous U.S., eastern Canada, western Alaska, southern South America, northwestern Africa, and most of Europe, Asia, and Australia. In contrast, cooler-than-average temperatures occurred throughout western Asia and from the north central to the southeastern United States.
According to the Australian Bureau of Meteorology (BoM), southeastern Australia experienced a cold outbreak during the last week of the month, setting several record lows. Charlotte Pass set a new Australian minimum temperature record for the month of April as temperatures dropped to -13.0°C (8.6°F) on April 29, while Mount Hotham set a state record for Victoria when temperatures fell to -8.2°C (17.2°F). A complete April 2009 Australian Climate Summary is available, courtesy of the BoM.
Sea surface temperatures during April 2009 were warmer than average across much of the world's oceans, with the exception of cooler-than-average conditions across parts of the northeastern Pacific, the central Atlantic, and the high-latitude and southern oceans. Some warming took place across the equatorial Pacific Ocean, resulting in warmer sea surface temperature anomalies in all Niño regions during April 2009 with respect to March 2009 anomalies. These conditions are indicative of a transition from a cold phase ENSO (La Niña) to ENSO-neutral conditions. Please see the April 2009 ENSO discussion for additional information.
The January-April 2009 map of temperature anomalies shows the presence of warmer-than-average conditions across much of the world's land areas, with the exception of cooler-than-average temperatures across parts of Alaska, southern Canada, northern Australia, eastern Russia, and northwestern South America. Sea surface temperatures were warmer than average across the North Indian and western Pacific oceans, and parts of the Atlantic Ocean. Cooler-than-average SSTs were present across the equatorial Pacific Ocean, along the western coasts of North America and northwestern Africa, and across most of the southern oceans.
The average position of the upper-level ridges of high pressure and troughs of low pressure (depicted by positive and negative 500-millibar height anomalies on the April 2009 map, respectively) are generally reflected by areas of positive and negative temperature anomalies at the surface, respectively. For other Global products, please see the Climate Monitoring Global Products page.
Images of sea surface temperature conditions are available for all weeks during 2009 from the weekly SST page.
Effective with the February 2006 report, NCDC transitioned from the use of the Operational Global Surface Temperature Index (Quayle et al. 1999) to the blended land and ocean dataset developed by Smith and Reynolds (2005). The differences between the two methods are discussed in Smith et al. (2005). The ranks found in the tables below are based on records that began in 1880.
April 2009 was the fifth warmest April since global surface records began in 1880 for combined global land and ocean surface temperatures. April land surface temperatures were fifth warmest, while ocean surface temperatures tied with 2003 as the fifth warmest in the 130-year record. The year-to-date (January-April) land and ocean combined temperature tied with 2003 as the sixth warmest on record.
| April | Anomaly | Rank (out of 130 years) |
Warmest (or Next Warmest) Year on Record |
|---|---|---|---|
GlobalLandOcean Land and Ocean |
+1.00°C (+1.80°F) +0.44°C (+0.79°F) +0.59°C (+1.06°F) |
5thwarmest 5th warmest 5th warmest |
2007 (+1.46°C/2.63°F) 1998 (+0.53°C/0.95°F) 1998 (+0.70°C/1.26°F) |
Northern HemisphereLandOcean Land and Ocean |
+1.06°C (+1.91°F) +0.38°C (+0.68°F) +0.64°C (+1.15°F) |
5th warmest 8th warmest 5th warmest |
2000 (+1.72°C/3.10°F) 2004 (+0.53°C/0.95°F) 2007 (+0.87°C/1.57°F) |
Southern HemisphereLandOcean Land and Ocean |
+0.78°C (+1.40°F) +0.49°C (+0.88°F) +0.53°C (+0.95°F) |
7th warmest 2nd warmest 4th warmest |
2005 (+1.13°C/2.03°F) 1998 (+0.59°C/1.06°F) 1998 (+0.63°C/1.13°F) |
| January- April |
Anomaly | Rank (out of 130 years) |
Warmest (or Next Warmest) Year on Record |
|---|---|---|---|
GlobalLandOcean Land and Ocean |
+0.92°C (+1.66°F) +0.40°C (+0.72°F) +0.54°C (+0.97°F) |
8th warmest 7th warmest 6th warmest |
2007 (+1.37°C/2.47°F) 1998 (+0.53°C/0.95°F) 2007 (+0.69°C/1.24°F) |
Northern HemisphereLandOcean Land and Ocean |
+1.00°C (+1.80°F) +0.34°C (+0.61°F) +0.59°C (+1.06°F) |
9th warmest 7th warmest 7th warmest |
2007 (+1.55°C/2.79°F) 2004 (+0.50°C/0.90°F) 2007 (+0.87°C/1.57°F) |
Southern HemisphereLandOcean Land and Ocean |
+0.65°C (+1.17°F) +0.46°C (+0.83°F) +0.48°C (+0.86°F) |
5th warmest 5th warmest 6th warmest |
2005 (+0.91°C/1.64°F) 1998 (+0.57°C/1.03°F) 1998 (+0.61°C/1.10°F) |
The most current data may be accessed via the Global Surface Temperature Anomalies page.
The maps below represent anomaly values based on the GHCN dataset of land surface stations using a base period of 1961-1990. Precipitation during April 2009 was highly variable. Above-average precipitation fell over eastern Australia, northeastern Brazil, western Europe, the midwestern and central U.S., and parts of southeastern Asia. The areas with the driest anomalies included much of South America, eastern Europe, Alaska's panhandle, and parts of eastern Asia.
During April 2009, heavy rain prompted devastating floods and mudslides that affected over 300,000 people and caused 38 fatalities in northeastern Brazil. The region experienced its worst deluge in more than 20 years.
Torrential downpours across Zambia and Namibia wreaked havoc across the region as rivers burst over their banks, flooding homes and cropland. The floods affected nearly 700,000 people in Zambia and 344,000 in Namibia.
Additional details on flooding and drought can also be found on the April 2009 Global Hazards page.
As shown in the adjacent animation, sea surface temperatures (SST) warmed across the equatorial Pacific during April 2009, resulting in warmer anomalies in all Niño regions when compared to March 2009 anomalies. The Oceanic Niño Index [three-month (February-March-April) running average] was -0.5°C (-0.9°F), which equals the threshold of -0.5°C (-0.9°F). A comprehensive summary of April 2009 ENSO conditions can be found on the ENSO monitoring page. For the latest advisory on ENSO conditions, please visit NOAA's Climate Prediction Center (CPC) and the CPC ENSO Diagnostic Discussion.
Images of sea surface temperature conditions are available for all weeks since 2003 at the weekly SST page.
As shown in the time series to the right, Northern Hemisphere snow cover extent during April 2009 was 1.4 million square kilometers below average, the ninth-lowest snow cover extent on record. Ten of the last eleven years had below-average snow cover extent and April 2009 was the sixth consecutive April with below-average snow cover extent. The 43-year average Northern Hemisphere April snow cover extent for the 1967-2009 period of record is 31.2 million square kilometers.
Across North America, snow cover for April 2009 was 0.39 million square kilometers above average, the 13th largest extent since satellite records began in 1967. The 43-year average North America April snow cover extent is 13.3 million square kilometers for the period of record. For information on the U.S. April snow events and U.S. snowfall records, please visit the U.S. 2008-2009 Snow Season Summary and the U.S. Records pages, respectively.
As depicted in the time series to the right, Eurasia's snow cover extent during April 2009 was 1.8 million square kilometers below average, the fourth-lowest snow cover extent on record. Much of this can be attributed to the above-normal temperatures that covered much of the Asian continent. The 43-year average Eurasian snow cover extent in April is 17.9 million square kilometers for the 1967-2009 period of record.
Data were provided by the Global Snow Laboratory, Rutgers University.
According to the National Snow and Ice Data Center, the April 2009 Northern Hemisphere sea ice extent, which is measured from passive microwave instruments onboard NOAA satellites, was below the 1979-2000 average. This was the tenth lowest April sea ice extent on record, 2.8 percent below the 1979-2000 average. April Arctic sea ice extent has decreased at an average rate of 2.8 percent per decade since 1979.
Meanwhile, the April 2009 Southern Hemisphere sea ice extent was 13.5 percent above the 1979-2000 average. This was the second largest sea ice extent in April, behind 2008. Southern Hemisphere sea ice extent for April has increased at an average rate of 3.0 percent per decade.
For further information on the Northern and Southern Hemisphere snow and ice conditions, please visit the NSIDC News page, provided by the NOAA's National Snow and Ice Data center (NSIDC).
Temperatures above the Earth's surface are measured within the lower troposphere, middle troposphere, and stratosphere using in-situ balloon-borne instruments (radiosondes) and polar-orbiting satellites (NOAA's TIROS-N). The radiosonde and satellite records have been adjusted to remove time-dependent biases (artificialities caused by changes in radiosonde instruments and measurement practices as well as changes in satellite instruments and orbital features through time). Global averages from radiosonde data are available from 1958 to present, while satellite measurements date back to 1979.
These temperatures are for the lowest 8 km (5 miles) of the atmosphere. Information on the University of Alabama in Huntsville (UAH) and Remote Sensing Systems (RSS) sources of troposphere data is available.
| April | Anomaly | Rank (out of 31 years) |
Warmest (or Next Warmest) Year on Record | Trend |
|---|---|---|---|---|
| UAH low-trop | +0.09°C/+0.16°F | 15th warmest | 1998 (+0.76°C/+1.37°F) | +0.11°C/decade |
| *RSS low-trop | +0.20°C/+0.36°F | 11th warmest | 1998 (+0.86°C/+1.54°F) | +0.17°C/decade |
*Version 03_0
| January- April |
Anomaly | Rank (out of 31 years) |
Warmest (or Next Warmest) Year on Record | Trend |
|---|---|---|---|---|
| UAH low-trop | +0.24°C/+0.43°F | 8th warmest | 1998 (+0.66°C/+1.19°F) | +0.15°C/decade |
| *RSS low-trop | +0.24°C/+0.43°F | 8th warmest | 1998 (+0.68°C/+1.22°F) | +0.16°C/decade |
*Version 03_0
These temperatures are for the atmospheric layer centered in the mid-troposphere (approximately 3-10 km (2-6 miles) above the Earth's surface), which also includes a portion of the lower stratosphere. (The Microwave Sounding Unit (MSU) channel used to measure mid-tropospheric temperatures receives about 25 percent of its signal above 10 km (6 miles).) Because the stratosphere has cooled due to increasing greenhouse gases in the troposphere and losses of ozone in the stratosphere, the stratospheric contribution to the tropospheric average, as measured from satellites, may create an artificial component of cooling to the mid-troposphere temperatures. The University of Washington (UW) versions of the UAH and RSS analyses attempt to remove the stratospheric influence from the mid-troposphere measurements, and as a result the UW versions tend to have a larger warming trend than either the UAH or RSS versions. For additional information, please see NCDC's Microwave Sounding Unit page.
The radiosonde data used in this global analysis were developed using the Lanzante, Klein, Seidel (2003) ("LKS") bias-adjusted dataset and the First Difference Method (Free et al. 2004) (RATPAC). Additional details are available. Satellite data have been adjusted by the Global Hydrology and Climate Center at the University of Alabama in Huntsville (UAH). An independent analysis is also performed by Remote Sensing Systems (RSS) and a third analysis has been performed by Dr. Qiang Fu of the University of Washington (UW) (Fu et al. 2004)** to remove the influence of the stratosphere on the mid-troposphere value. Global averages from radiosonde data are available from 1958 to present, while satellite measurements began in 1979.
Radiosonde measurements indicate that, for the January-April year-to-date period, temperatures in the mid-troposphere were 0.42°C (0.76°F) above average, resulting in the ninth warmest January-April since global radiosonde measurements began in 1958. However, as shown in the table below, satellite analyses of the January-April year-to-date period for the middle troposphere varied from ninth to fourteenth warmest on record.
The global mid-troposphere temperatures were near to above average in April 2009. As shown in the table below, satellite measurement for April 2009 ranked from 16th warmest to 19th warmest on record.
| April | Anomaly | Rank (out of 31 years) |
Warmest (or Next Warmest) Year on Record | Trend |
|---|---|---|---|---|
| UAH mid-trop | -0.04°C/-0.07°F | 19th warmest | 1998 (+0.71°C/+1.28°F) | +0.02°C/decade |
| *RSS mid-trop | +0.04°C/+0.07°F | 16th warmest | 1998 (+0.75°C/+1.35°F) | +0.08°C/decade |
| **UW-UAH mid-trop | +0.05°C/+0.08°F | 16th warmest | 1998 (+0.85°C/+1.53°F) | +0.08°C/decade |
| **UW-*RSS mid-trop | +0.11°C/+0.20°F | 16th warmest | 1998 (+0.88°C/+1.58°F) | +0.13°C/decade |
*Version 03_0
| January- April |
Anomaly | Rank (out of 31 years) |
Warmest (or Next Warmest) Year on Record | Trend |
|---|---|---|---|---|
| UAH mid-trop | +0.05°C/+0.09°F | 14th warmest | 1998 (+0.60°C/+1.08°F) | +0.05°C/decade |
| *RSS mid-trop | +0.09°C/+0.16°F | 13th warmest | 1998 (+0.63°C/+1.13°F) | +0.09°C/decade |
| **UW-UAH mid-trop | +0.16°C/+0.29°F | 9th warmest | 1998 (+0.73°C/+1.31°F) | +0.11°C/decade |
| **UW-*RSS mid-trop | +0.18°C/+0.32°F | 10th warmest | 1998 (+0.75°C/+1.35°F) | +0.15°C/decade |
| RATPAC | +0.42°C/+0.76°F | 9th warmest | 1998 (+0.75°C/+1.34°F) | +0.14°C/decade |
*Version 03_0
The table below summarizes stratospheric conditions for April 2009. On average, the stratosphere is located approximately 16-23 km (10-14 miles) above the Earth's surface. Over the last decade, stratospheric temperatures have been below average in part due to the depletion of ozone. The large positive anomaly in 1982 was caused by the volcanic eruption of El Chichon in Mexico, and the sharp jump in temperature in 1991 was a result of the eruption of Mt. Pinatubo in the Philippines. In both cases the temperatures returned to pre-eruption levels within two years.
| April | Anomaly | Rank (out of 31 years) |
Coolest Year on Record |
|---|---|---|---|
| UAH stratosphere | -0.42°C (-0.76°F) | 10th coolest | 1999 (-0.72°C/-1.30°F) |
| *RSS stratosphere | -0.34°C (-0.60°F) | 11th coolest | 1999 (-0.65°C/-1.16°F) |
*Version 03_0
For additional details on precipitation and temperatures in April, see the Global Hazards page.
Christy, John R., R.W. Spencer, and W.D. Braswell, 2000: MSU tropospheric Temperatures: Dataset Construction and Radiosonde Comparisons. J. of Atmos. and Oceanic Technology, 17, 1153-1170.
Free, M., D.J. Seidel, J.K. Angell, J. Lanzante, I. Durre and T.C. Peterson (2005) Radiosonde Atmospheric Temperature Products for Assessing Climate (RATPAC): A new dataset of large-area anomaly time series, J. Geophys. Res., 10.1029/2005JD006169.
Free, M., J.K. Angell, I. Durre, J. Lanzante, T.C. Peterson and D.J. Seidel(2004), Using first differences to reduce inhomogeneity in radiosonde temperature datasets, J. Climate, 21, 4171-4179.
Fu, Q., C.M. Johanson, S.G. Warren, and D.J. Seidel, 2004: Contribution of stratospheric cooling to satellite-inferred tropospheric temperature trends. Nature, 429, 55-58.
Lanzante, J.R., S.A. Klein, and D.J. Seidel (2003a), Temporal homogenization of monthly radiosonde temperature data. Part I: Methodology, J. Climate, 16, 224-240.
Lanzante, J.R., S.A. Klein, and D.J. Seidel (2003b), Temporal homogenization of monthly radiosonde temperature data. Part II: trends, sensitivities, and MSU comparison, J. Climate, 16, 241 262.
Mears, Carl A., M.C. Schabel, F.J. Wentz, 2003: A Reanalysis of the MSU Channel 2 tropospheric Temperature Record. J. Clim, 16, 3650-3664.
Peterson, T.C. and R.S. Vose, 1997: An Overview of the Global Historical Climatology Network Database. Bull. Amer. Meteorol. Soc., 78, 2837-2849.
Quayle, R.G., T.C. Peterson, A.N. Basist, and C. S. Godfrey, 1999: An operational near-real-time global temperature index. Geophys. Res. Lett., 26, 333-335.
Smith, T.M., and R.W. Reynolds (2005), A global merged land air and sea surface temperature reconstruction based on historical observations (1880-1997), J. Clim., 18, 2021-2036.
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