Evaluating the Differences between NCEP’s 20th Century Forecast Variables and Analysis Variables

Introduction to NCEP’s 20th Century Daily Forecast and Analysis Variables

The National Centers for Environmental Prediction (NCEP) has a long history of producing high-quality reanalysis datasets, which combine observations from multiple sources with numerical weather prediction models to provide a comprehensive and consistent representation of Earth’s atmospheric conditions. One such dataset is the NCEP 20th Century Reanalysis, which covers the period from 1871 to 2015. This dataset provides a wealth of information, including both forecast and analysis variables, that can be instrumental in understanding the Earth’s climate and weather patterns over the past century.

The distinction between forecast and analysis variables in the NCEP 20th Century Reanalysis is an important aspect to understand, as it reveals the different ways in which the data are generated and can be used. In this article, we will examine the key differences between these two types of variables, exploring their respective characteristics, applications, and the importance of understanding their nuances.

Predictive Variables

Forecast variables in the NCEP 20th Century Reanalysis are the output of the numerical weather prediction model used to generate the reanalysis. These variables represent the model’s prediction of future atmospheric conditions based on the assimilation of observational data and the application of physical laws governing the behavior of the atmosphere. Forecast variables include parameters such as temperature, wind, humidity, and precipitation.

The primary advantage of forecast variables is their ability to provide a consistent, four-dimensional (three spatial dimensions and time) representation of the evolution of the atmosphere. This information can be particularly valuable for studying long-term trends, identifying patterns, and investigating the drivers of climate variability. In addition, forecast variables can be used to initialize and validate other numerical models, thereby contributing to the advancement of our understanding of the Earth’s climate system.

Analysis Variables

Unlike forecast variables, analysis variables in the NCEP 20th Century Reanalysis are the result of a data assimilation process that combines observational data with the model forecast to provide the best estimate of the actual atmospheric state at a given time. The goal of this process is to minimize discrepancies between model predictions and available observations, resulting in a more accurate representation of physical reality.

Analysis variables are often considered more accurate than forecast variables because they incorporate the latest observational information. This makes analysis variables particularly useful for studying the historical evolution of atmospheric phenomena such as weather patterns, extreme events, and climate indices. In addition, analysis variables can serve as a valuable reference for validating other data sets or for initializing high-resolution regional models.

Practical applications and considerations

The differences between forecast and analysis variables in the NCEP 20th Century Reanalysis have important implications for their practical applications. Forecast variables are well suited for long-term studies and climate model validation because they provide a continuous and consistent representation of atmospheric evolution. Analysis variables, on the other hand, are more appropriate for investigating specific historical events or for initializing high-resolution models designed to capture the nuances of atmospheric state.

When working with the NCEP 20th Century Reanalysis, it is critical to consider the relative strengths and limitations of both forecast and analysis variables. Researchers should carefully select the appropriate variables based on their research objectives and the specific questions they are trying to answer. By understanding the differences between these two types of variables, scientists can take full advantage of the NCEP 20th Century Reanalysis and contribute to our understanding of the Earth’s climate system and its evolution over the past century.

Conclusion

The NCEP 20th Century Reanalysis is a valuable resource for climate and weather research, providing a wealth of information in the form of forecast and analysis variables. Understanding the key differences between these two types of variables is essential to effectively using the dataset and deriving meaningful insights. By exploring the characteristics, applications, and considerations associated with forecast and analysis variables, researchers can unlock the full potential of the NCEP 20th Century Reanalysis to advance our understanding of the Earth’s climate and atmospheric processes.

FAQs

Difference between NCEP’s 20th Century daily Forecast and Analysis variables

The main difference between the 20th Century daily Forecast and Analysis variables from NCEP (National Centers for Environmental Prediction) is that the Forecast variables are the output of a numerical weather prediction model, while the Analysis variables are the result of assimilating observational data into the model to provide a more accurate representation of the current state of the atmosphere.

The Forecast variables are the model’s best estimate of future atmospheric conditions based on the current state and the underlying physics and dynamics. They include variables such as temperature, humidity, wind, precipitation, and pressure at various levels in the atmosphere. These forecasts are produced by running the model forward in time from the initial conditions.

The Analysis variables, on the other hand, are the result of combining the model forecast with observational data from a variety of sources, such as surface weather stations, weather balloons, satellites, and other instruments. This process, known as data assimilation, allows the model to be adjusted to better match the observed conditions, resulting in a more accurate representation of the current state of the atmosphere. The Analysis variables are often used as the initial conditions for the next forecast cycle.

What is the purpose of the 20th Century daily Forecast and Analysis data from NCEP?

The 20th Century daily Forecast and Analysis data from NCEP serve several important purposes:

1. Operational weather forecasting: The Forecast data are used as input to numerical weather prediction models to produce operational weather forecasts, which are essential for a wide range of applications, such as aviation, agriculture, and disaster preparedness.

2. Climate research and modeling: The Analysis data provide a comprehensive, long-term dataset of atmospheric conditions, which can be used to study climate variability and change, as well as to develop and validate climate models.

3. Atmospheric research: Both the Forecast and Analysis data are valuable resources for atmospheric scientists, who use them to study a wide range of atmospheric phenomena, such as weather systems, climate patterns, and atmospheric processes.

4. Reanalysis projects: The Analysis data are often used as the starting point for reanalysis projects, which combine observational data with numerical models to create a comprehensive, consistent, and homogeneous dataset of the Earth’s atmosphere, oceans, and land surface over an extended period.

What are the spatial and temporal resolutions of the 20th Century daily Forecast and Analysis data from NCEP?

The spatial and temporal resolutions of the 20th Century daily Forecast and Analysis data from NCEP vary depending on the specific dataset and the time period of interest.

For the 20th Century Reanalysis project, which covers the period from 1851 to 2014, the spatial resolution of the Analysis data is approximately 2 degrees in latitude and longitude, with 28 vertical levels. The temporal resolution is 6-hourly.

For the more recent NCEP/NCAR Reanalysis, which covers the period from 1948 to the present, the spatial resolution of the Analysis data is approximately 2.5 degrees in latitude and longitude, with 17 vertical levels. The temporal resolution is also 6-hourly.

The Forecast data, on the other hand, are typically available at higher spatial and temporal resolutions, depending on the specific model and forecast lead time. For example, the NCEP Global Forecast System (GFS) model produces forecasts at a spatial resolution of approximately 0.25 degrees in latitude and longitude, with 64 vertical levels, and a temporal resolution of 3 hours.

What are the main variables included in the 20th Century daily Forecast and Analysis data from NCEP?

The 20th Century daily Forecast and Analysis data from NCEP include a wide range of atmospheric variables, including:

• Temperature (at various levels in the atmosphere)
• Geopotential height (at various pressure levels)
• Humidity (specific humidity, relative humidity, and dew point)
• Wind speed and direction (at various levels)
• Precipitation (total, convective, and stratiform)
• Sea level pressure
• Surface fluxes (such as sensible and latent heat fluxes)
• Vertical velocity (or omega)
• Cloud cover and cloud water content
• Soil moisture and temperature

These variables are crucial for understanding and modeling the complex interactions between the atmosphere, land, and ocean, and are used in a wide range of applications, from weather forecasting to climate research and impact assessment.

How can users access and download the 20th Century daily Forecast and Analysis data from NCEP?

Users can access and download the 20th Century daily Forecast and Analysis data from NCEP through several channels:

1. NCEP/NCAR Reanalysis data: The NCEP/NCAR Reanalysis dataset, which covers the period from 1948 to the present, is available for download from the NOAA Physical Sciences Laboratory (PSL) website (https://psl.noaa.gov/data/gridded/data.ncep.reanalysis.html).

2. 20th Century Reanalysis data: The 20th Century Reanalysis dataset, which covers the period from 1851 to 2014, can be accessed and downloaded from the NOAA/CIRES Climate Data Guide website (https://climatedataguide.ucar.edu/climate-data/20th-century-reanalysis-version-2c-and-version-3).

3. NCEP Global Forecast System (GFS) data: The NCEP GFS Forecast data are available for download from the NOAA National Centers for Environmental Information (NCEI) website (https://www.ncei.noaa.gov/products/weather-climate-models/global-forecast).

Users can download the data in various file formats, such as NetCDF, GRIB, or ASCII, depending on their specific needs and the analysis software they are using. Additionally, some of the data may be available through web services or APIs, which can simplify the data retrieval process.