# Circulation and Climate Variability in the Czech Republic between 1961 and 2020: A Comparison of Changes for Two “Normal” Periods

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## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Study Area

^{2}, is located in central Europe (Figure 1). This position is influenced by the effects of the Atlantic Ocean, the Mediterranean Sea, and the Eurasian continent, which determines the temperature and humidity of air masses moving into central Europe. These airflow effects are modified at regional/local scales by orographic patterns (altitude, leeward, and windward effects) because altitudes over the CR territory range from 115 to 1603 m (mean altitude 390 m a.s.l.). According to the Köppen classification, the major part of the CR territory corresponds to the climate category of temperate broadleaf deciduous forest (Cfb), while the remaining areas are attributed to a boreal climate (particularly Dfb—boreal climate with warm summer, and, to a lesser extent, Dfc—boreal climate with cold summer; for more detail see [13]).

#### 2.2. Meteorological Data

- (i)
- Sunshine duration—79 stations;
- (ii)
- Mean, maximum, and minimum temperatures—133 stations;
- (iii)
- Relative humidity—133 stations;
- (iv)
- Precipitation total—531 stations;
- (v)
- Wind speed—119 stations.

#### 2.3. Circulation Types

- (i)
- Nine anticyclonic types (A, AN, ANE, AE, ASE, AS, ASW, AW, ANW);
- (ii)
- Nine cyclonic types (C, CN, CNE, CE, CSE, CS, CSW, CW, CNW);
- (iii)
- Eight directional types (N, NE, E, SE, S, SW, W, NW);
- (iv)
- An unclassified type U.

#### 2.4. Methods

#### 2.4.1. Homogenisation

- (i)
- Quality control of daily data (comparison with neighbouring stations);
- (ii)
- (iii)
- Adjustment of the daily data (with respect to existing metadata and the evaluation of the importance of break-points detected, applying our own method of Distribution Adjustment by Percentile, developed from the “variable correction method” by [26]);
- (iv)
- Filling gaps (by interpolation methods from neighbouring stations with respect to differences in their distance and altitude and correlation coefficients) [21].

#### 2.4.2. Statistical Analysis

## 3. Results

#### 3.1. Circulation Patterns

#### 3.2. Sunshine

#### 3.3. Temperature

#### 3.4. Humidity

#### 3.5. Precipitation

#### 3.6. Wind Speed

^{−1}in 1991–2020 compared to the preceding 30 years, and all of these differences were statistically significant (Table 8). While in 1961–1990, none of the calculated annual and seasonal linear trends were statistically significant at the 0.05 significance level, in the second 30-year period, all except DJF were decreasing and statistically significant (c. 0.1 m s

^{−1}/10 years). Similarly, differences in trend slopes were significant for all series with the exception of DJF. Variability characterised by the coefficient of variation (Table 8) significantly increased for the annual and MAM series in the second period and the same two series indicated a significant change in asymmetry as the skewness increased from negative values to positive ones. This means a tendency toward a longer and fatter tail on the right side of the distribution where the extremely large values of mean wind speed may occur. Differences in the distribution of mean wind speeds are quite substantial. Except for DJF, the annual and remaining seasonal series show important declines in percentile values (Figure 11b). For example, the values of the upper quartile during 1991–2020 are close to or deeply below the values of lower quartiles over the preceding 30 years. It is a clear indication of important changes in the character of the distribution of annual and seasonal mean wind speeds that a shift is shown to lower values in density functions. This is remarkable, particularly for the annual and MAM series (Figure 11c). Differences in density functions were significant for all series.

#### 3.7. Spatial Patterns

## 4. Discussion

## 5. Conclusions

- (i)
- Mean frequencies of anticyclonic and cyclonic circulation types according to the objective classification express generally significant changes between both 30-year normal sub-periods. Significant increases in their 30-year means appear for frequencies of days with the occurrence of anticyclonic types and decreases for cyclonic types in the 1991–2020 period compared to 1961–1990. Directional circulation types exhibit relatively stable patterns in both periods analysed;
- (ii)
- Annual and seasonal sunshine duration series do not express significant changes between two 30-year normal periods in terms of their variability, characteristics of distribution, density functions, or linear trends. Only an increase in annual, MAM, and JJA means in 1991–2020 compared to the preceding period was statistically significant;
- (iii)
- Mean, maximum, and minimum temperatures display different patterns in two 30-year normal periods in accord with recent warming. They are reflected in statistically significant differences in means, characteristics of distribution, density functions, and significant linear trends through 1991–2020 (annual, JJA, SON). This is particularly pronounced for the JJA series;
- (iv)
- Statistically significant decreases in means of relative humidity between two 30-year normal periods (except SON) are reflected in a significant shift of density functions to lower values. However, decreasing linear trends were significant only for MAM. Increasing variability in relative humidity was significant for the annual and MAM series.
- (v)
- Precipitation totals of both 30-year periods are represented well by non-significant linear trends. There are no substantial changes in mean and variability nor in the character of their distributions represented by the density functions;
- (vi)
- Wind speed in two 30-year normal periods represents quite different patterns expressed by statistically significant decreasing linear trends over 1991–2020, significant differences in means (partly in variability and skewness, both annual and MAM), and in density functions;
- (vii)
- The recent 30-year normal 1991–2020 period is strongly influenced by recent climate change. This is reflected in statistically significant changes in means, variability, characteristics of distribution, density functions, and linear trends compared to the preceding 30-year normal of 1961–1990. These features have already become typical for many climatic variables;
- (viii)
- Spatial patterns of differences between two 30-year periods for annual series of climate variables generally confirm knowledge obtained from the mean series for the whole CR. Spatial differences for temperature characteristics are territorially the most consistent, while for other climate variables, spatial patterns are slightly complicated;
- (ix)
- All the above knowledge has to be considered when selecting a proper “baseline” or reference period for climate change impact and adaptation studies.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Appendix A

- (i)
- Anticyclonic circulation types

- (ii)
- Cyclonic circulation types

- (iii)
- Directional circulation types

## Appendix B

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**Figure 1.**(

**a**) The location of the Czech Republic in Europe, (

**b**) the physical geographical map of the Czech Republic, and the network of meteorological stations of the Czech Hydrometeorological Institute used for the calculation of (

**c**) sunshine duration, (

**d**) temperatures and relative humidity, (

**e**) precipitation totals, and (

**f**) wind speed.

**Figure 2.**Annual and seasonal frequencies of days with anticyclonic circulation types according to the objective classification for the territory of the Czech Republic in the 1961–2020 period: (

**a**) fluctuations with linear trends in the entire period, 1961–1990 and 1991–2020; (

**b**) box plots (median, lower and upper quartile, minimum, and maximum) for 1961–2020 (1), 1961–1990 (2), and 1991–2020 (3); (

**c**) the density distribution of the series in 1961–1990 and 1991–2020. The density curves outside the reference band (green–blue) indicate a significant difference in the two distributions (and vice versa).

**Figure 3.**Annual and seasonal frequencies of days with cyclonic circulation types according to the objective classification for the territory of the Czech Republic in the 1961–2020 period: (

**a**) fluctuations with linear trends in the entire period, 1961–1990 and 1991–2020; (

**b**) box plots (median, lower and upper quartile, minimum, and maximum) for 1961–2020 (1), 1961–1990 (2), and 1991–2020 (3); (

**c**) the density distribution of the series in 1961–1990 and 1991–2020. The density curves outside the reference band (green–blue) indicate a significant difference in the two distributions (and vice versa).

**Figure 4.**Annual and seasonal frequencies of days with directional circulation types according to the objective classification for the territory of the Czech Republic in the 1961–2020 period: (

**a**) fluctuations with linear trends in the entire period, 1961–1990 and 1991–2020; (

**b**) box plots (median, lower and upper quartile, minimum, and maximum) for 1961–2020 (1), 1961–1990 (2), and 1991–2020 (3); (

**c**) the density distribution of the series in 1961–1990 and 1991–2020. The density curves outside the reference band (green–blue) indicate a significant difference in the two distributions (and vice versa).

**Figure 5.**Mean annual and seasonal series of sunshine duration for the territory of the Czech Republic in the 1961–2020 period: (

**a**) fluctuations with linear trends in the entire period, 1961–1990 and 1991–2020; (

**b**) box plots (median, lower and upper quartile, minimum, and maximum) for 1961–2020 (1), 1961–1990 (2), and 1991–2020 (3); (

**c**) the density distribution of the series in 1961–1990 and 1991–2020. The density curves outside the reference band (green–blue) indicate a significant difference in the two distributions (and vice versa).

**Figure 6.**Mean annual and seasonal temperature series for the territory of the Czech Republic in the 1961–2020 period: (

**a**) fluctuations with linear trends in the entire period, 1961–1990 and 1991–2020; (

**b**) box plots (median, lower and upper quartile, minimum, and maximum) for 1961–2020 (1), 1961–1990 (2), and 1991–2020 (3); (

**c**) the density distribution of the series in 1961–1990 and 1991–2020. The density curves outside the reference band (green–blue) indicate a significant difference in the two distributions (and vice versa).

**Figure 7.**Annual and seasonal mean maximum temperature series for the territory of the Czech Republic in the 1961–2020 period: (

**a**) fluctuations with linear trends in the entire period, 1961–1990 and 1991–2020; (

**b**) box plots (median, lower and upper quartile, minimum, and maximum) for 1961–2020 (1), 1961–1990 (2), and 1991–2020 (3); (

**c**) the density distribution of the series in 1961–1990 and 1991–2020. The density curves outside the reference band (green–blue) indicate a significant difference in the two distributions (and vice versa).

**Figure 8.**Annual and seasonal mean minimum temperature series for the territory of the Czech Republic in the 1961–2020 period: (

**a**) fluctuations with linear trends in the entire period, 1961–1990 and 1991–2020; (

**b**) box plots (median, lower and upper quartile, minimum, and maximum) for 1961–2020 (1), 1961–1990 (2), and 1991–2020 (3); (

**c**) the density distribution of the series in 1961–1990 and 1991–2020. The density curves outside the reference band (green–blue) indicate a significant difference in the two distributions (and vice versa).

**Figure 9.**Annual and seasonal mean relative humidity series for the territory of the Czech Republic in the 1961–2020 period: (

**a**) fluctuations with linear trends in the entire period, 1961–1990 and 1991–2020; (

**b**) box plots (median, lower and upper quartile, minimum, and maximum) for 1961–2020 (1), 1961–1990 (2), and 1991–2020 (3); (

**c**) the density distribution of the series in 1961–1990 and 1991–2020. The density curves outside the reference band (green–blue) indicate a significant difference in the two distributions (and vice versa).

**Figure 10.**Annual and seasonal series of mean precipitation totals for the territory of the Czech Republic in the 1961–2020 period: (

**a**) fluctuations with linear trends in the entire period, 1961–1990 and 1991–2020; (

**b**) box plots (median, lower and upper quartile, minimum, and maximum) for 1961–2020 (1), 1961–1990 (2), and 1991–2020 (3); (

**c**) the density distribution of the series in 1961–1990 and 1991–2020. The density curves outside the reference band (green–blue) indicate a significant difference in the two distributions (and vice versa).

**Figure 11.**Annual and seasonal series of mean wind speed for the territory of the Czech Republic in the 1961–2020 period: (

**a**) fluctuations with linear trends in the entire period, 1961–1990 and 1991–2020; (

**b**) box plots (median, lower and upper quartile, minimum, and maximum) for 1961–2020 (1), 1961–1990 (2) and 1991–2020 (3); (

**c**) the density distribution of the series in 1961–1990 and 1991–2020. The density curves outside the reference band (green–blue) indicate a significant difference in the two distributions (and vice versa).

**Figure 12.**Spatial distribution of differences between the 1991–2020 and 1961–1990 periods over the territory of the Czech Republic for the annual series of selected climate variables: (

**a**) sunshine duration, (

**b**) mean temperature, (

**c**) maximum temperature, (

**d**) minimum temperature, (

**e**) relative humidity, (

**f**) precipitation total, and (

**g**) wind speed. The individual maps were created based on the number of stations specified in Section 2.2.

**Table 1.**Selected statistical characteristics of annual (Ann) and seasonal (DJF, MAM, JJA, and SON) frequencies of days with anticyclonic, cyclonic, and directional circulation types according to the objective classification for the territory of the Czech Republic during the 1961–1990 (A) and 1991–2020 (B) periods: means are in days, variation coefficients (CV) in %, and linear trends in days/10 years (in bold statistically significant at the 0.05 significance level). An asterisk * indicates statistically significant differences of a given characteristic between two 30-year periods.

Season | Period | Mean | CV | Skewness | Kurtosis | Slope | |||
---|---|---|---|---|---|---|---|---|---|

Anticyclonic circulation types | |||||||||

Ann | A | 149.4 | * | 15.5 | −0.18 | −0.57 | 14.2 | ||

B | 167.4 | * | 13.5 | −0.09 | −0.40 | 2.5 | |||

DJF | A | 38.2 | * | 28.2 | 0.80 | 0.11 | 1.2 | ||

B | 44.2 | * | 24.1 | −0.11 | −0.17 | −2.1 | |||

MAM | A | 26.9 | * | 28.4 | 0.46 | 0.55 | 0.9 | ||

B | 33.7 | * | 25.6 | 0.76 | 0.02 | 0.9 | |||

JJA | A | 40.6 | * | 22.9 | −0.34 | −0.36 | 6.8 | ||

B | 47.8 | * | 17.0 | −0.10 | −1.12 | 1.2 | |||

SON | A | 43.8 | 27.2 | −0.18 | −0.77 | 5.0 | |||

B | 41.8 | 24.7 | 0.23 | −0.03 | 0.9 | ||||

Cyclonic circulation types | |||||||||

Ann | A | 67.6 | * | 28.1 | 0.66 | 0.42 | −14.4 | ||

B | 55.7 | * | 20.5 | 0.28 | 0.94 | 0.0 | |||

DJF | A | 12.9 | 46.9 | 0.12 | * | −0.54 | * | −1.4 | |

B | 10.5 | 52.2 | 1.92 | * | 6.00 | * | 0.8 | ||

MAM | A | 25.9 | * | 28.4 | 0.32 | 0.02 | −3.3 | ||

B | 19.5 | * | 30.3 | −0.10 | −0.06 | −1.2 | |||

JJA | A | 16.1 | * | 47.7 | 0.51 | −0.15 | −5.4 | ||

B | 12.0 | * | 45.5 | 1.10 | 0.74 | 0.5 | |||

SON | A | 12.6 | 52.4 | 0.46 | −0.59 | −3.8 | |||

B | 13.7 | 43.2 | 0.55 | −0.46 | 0.0 | ||||

Directional circulation types | |||||||||

Ann | A | 142.1 | 7.7 | 0.69 | −0.14 | 0.0 | |||

B | 136.1 | 10.6 | −0.14 | 0.12 | −3.3 | ||||

DJF | A | 38.5 | 18.5 | −0.36 | 0.37 | −0.5 | |||

B | 35.2 | 23.0 | 0.27 | 0.01 | 0.6 | ||||

MAM | A | 37.8 | 14.9 | −0.42 | 0.23 | 2.4 | |||

B | 37.3 | 14.4 | −0.42 | −0.16 | −0.5 | ||||

JJA | A | 32.2 | * | 14.7 | 0.10 | 1.00 | 0.0 | ||

B | 28.8 | * | 19.9 | −0.36 | −0.38 | −1.1 | |||

SON | A | 33.6 | 22.0 | 0.22 | −0.67 | −0.5 | |||

B | 34.8 | 20.0 | −0.27 | 0.46 | −3.2 |

**Table 2.**Selected statistical characteristics of mean annual (Ann) and seasonal (DJF, MAM, JJA, and SON) sunshine duration series in the Czech Republic during the 1961–1990 (A) and 1991–2020 (B) periods: means are in hours, coefficients of variation (CV) in %, linear trends in hours/10 years (none statistically significant at the 0.05 significance level). An asterisk * indicates statistically significant differences of a given characteristic between two 30-year periods.

Season | Period | Mean | CV | Skewness | Kurtosis | Slope | ||
---|---|---|---|---|---|---|---|---|

Ann | A | 1613.9 | * | 7.3 | −0.14 | −1.33 | −15.4 | |

B | 1687.1 | * | 7.6 | 0.50 | 0.22 | 15.3 | ||

DJF | A | 164.4 | 19.2 | 0.47 | * | −0.34 | 1.5 | |

B | 168.7 | 16.4 | −0.84 | * | 0.94 | −8.5 | ||

MAM | A | 482.5 | * | 10.8 | 0.28 | −0.20 | 11.6 | |

B | 524.9 | * | 14.8 | 0.01 | −0.10 | 13.6 | ||

JJA | A | 624.8 | * | 9.3 | −0.04 | −0.81 | −11.9 | |

B | 677.8 | * | 7.8 | 1.18 | 1.40 | –2.2 | ||

SON | A | 335.7 | 13.9 | −0.26 | −0.98 | −15.8 | ||

B | 315.9 | 18.8 | 0.29 | −0.52 | 5.8 |

**Table 3.**Selected statistical characteristics of mean annual (Ann) and seasonal (DJF, MAM, JJA, and SON) temperature series in the Czech Republic in the 1961–1990 (A) and 1991–2020 (B) periods: means and standard deviations (SD) are in °C, linear trends in °C/10 years (in bold statistically significant at the 0.05 significance level). An asterisk * indicates statistically significant differences of a given characteristic between two 30-year periods.

Season | Period | Mean | SD | Skewness | Kurtosis | Slope | |||
---|---|---|---|---|---|---|---|---|---|

Ann | A | 7.4 | * | 0.6 | 0.01 | −1.08 | * | 0.25 | |

B | 8.5 | * | 0.8 | −0.48 | 0.23 | * | 0.56 | ||

DJF | A | −1.7 | * | 2.0 | −0.66 | 0.45 | 0.59 | ||

B | −0.7 | * | 1.7 | 0.05 | −0.67 | 0.53 | |||

MAM | A | 7.3 | * | 1.0 | −0.34 | −0.68 | 0.34 | ||

B | 8.4 | * | 1.0 | −0.18 | −0.71 | 0.44 | |||

JJA | A | 16.2 | * | 0.7 | 0.02 | 0.26 | 0.02 | ||

B | 17.7 | * | 1.0 | 0.41 | −0.66 | 0.53 | |||

SON | A | 7.8 | * | 0.9 | 0.09 | −0.96 | −0.14 | * | |

B | 8.4 | * | 1.0 | 0.18 | −0.30 | 0.62 | * |

**Table 4.**Selected statistical characteristics of annual (Ann) and seasonal (DJF, MAM, JJA, and SON) mean maximum temperature series in the Czech Republic in the 1961–1990 (A) and 1991–2020 (B) periods: means and standard deviations (SD) are in °C, linear trends in °C/10 years (in bold statistically significant at the 0.05 significance level). An asterisk * indicates statistically significant differences of a given characteristic between two 30-year periods.

Season | Period | Mean | SD | Skewness | Kurtosis | Slope | ||
---|---|---|---|---|---|---|---|---|

Ann | A | 12.0 | * | 0.7 | 0.14 | −0.80 | 0.20 | |

B | 13.2 | * | 0.9 | −0.46 | 0.43 | 0.63 | ||

DJF | A | 1.3 | * | 1.9 | −0.34 | 0.29 | 0.58 | |

B | 2.4 | * | 1.7 | 0.08 | −0.78 | 0.50 | ||

MAM | A | 12.4 | * | 1.2 | −0.37 | −0.38 | 0.36 | |

B | 13.8 | * | 1.3 | −0.20 | −0.65 | 0.67 | ||

JJA | A | 21.9 | * | 0.9 | 0.32 | −0.19 | 0.02 | |

B | 23.8 | * | 1.2 | 0.59 | −0.54 | 0.62 | ||

SON | A | 12.4 | 1.0 | 0.54 | −0.22 | –0.14 | * | |

B | 12.8 | 1.2 | 0.16 | 0.03 | 0.74 | * |

**Table 5.**Selected statistical characteristics of annual (Ann) and seasonal (DJF, MAM, JJA, and SON) mean minimum temperature series in the Czech Republic in the 1961–1990 (A) and 1991–2020 (B) periods: means and standard deviations (SD) are in °C, linear trends in °C/10 years (in bold statistically significant at the 0.05 significance level). An asterisk * indicates statistically significant differences of a given characteristic between two 30-year periods.

Season | Period | Mean | SD | Skewness | Kurtosis | Slope | ||
---|---|---|---|---|---|---|---|---|

Ann | A | 3.1 | * | 0.6 | −0.10 | −0.91 | 0.24 | |

B | 4.0 | * | 0.7 | −0.37 | −0.22 | 0.51 | ||

DJF | A | −4.7 | 2.2 | −0.73 | 0.49 | 0.59 | ||

B | −3.7 | 1.8 | 0.05 | −0.71 | 0.64 | |||

MAM | A | 2.4 | * | 0.9 | −0.28 | −0.85 | 0.24 | |

B | 3.2 | * | 0.8 | −0.15 | −0.80 | 0.29 | ||

JJA | A | 10.6 | * | 0.6 | −0.88 | 0.95 | 0.05 | * |

B | 12.0 | * | 0.7 | −0.17 | −0.27 | 0.51 | * | |

SON | A | 3.9 | * | 1.0 | −0.24 | −1.15 | 0.00 | * |

B | 4.6 | * | 0.9 | 0.28 | 0.30 | 0.62 | * |

**Table 6.**Selected statistical characteristics of annual (Ann) and seasonal (DJF, MAM, JJA, and SON) mean relative humidity series in the Czech Republic in the 1961–1990 (A) and 1991–2020 (B) periods: means and standard deviations (SD) are in %, linear trends in %/10 years (in bold statistically significant at the 0.05 significance level). The asterisk * indicates statistically significant differences of a given characteristic between two 30-year periods.

Season | Period | Mean | SD | Skewness | Kurtosis | Slope | ||
---|---|---|---|---|---|---|---|---|

Ann | A | 79 | * | 1.3 | * | −0.35 | 0.11 | −0.6 |

B | 78 | * | 1.9 | * | −0.55 | −0.21 | −1.0 | |

DJF | A | 86 | * | 1.3 | –0.84 | 0.75 | –0.5 | |

B | 84 | * | 1.4 | −0.43 | −0.35 | −0.5 | ||

MAM | A | 75 | * | 2.2 | * | 0.06 | −0.16 | −1.3 |

B | 72 | * | 3.5 | * | −0.52 | −0.10 | −1.9 | |

JJA | A | 74 | * | 2.8 | −1.02 | 0.96 | −0.2 | |

B | 71 | * | 3.5 | −0.96 | −0.24 | −1.0 | ||

SON | A | 82 | 1.9 | −0.79 | 1.43 | −0.2 | ||

B | 83 | 2.2 | −0.31 | 0.58 | −0.2 |

**Table 7.**Selected statistical characteristics of annual (Ann) and seasonal (DJF, MAM, JJA, and SON) series of mean precipitation totals in the Czech Republic in the 1961–1990 (A) and 1991–2020 (B) periods: means are in mm, coefficients of variation (CV) in %, linear trends in mm/10 years (none statistically significant at the 0.05 significance level). An asterisk * indicates statistically significant differences of a given characteristic between two 30-year periods.

Season | Period | Mean | CV | Skewness | Kurtosis | Slope | |
---|---|---|---|---|---|---|---|

Ann | A | 681 | 12.8 | 0.44 | –0.84 | −2.4 | |

B | 699 | 12.7 | 0.01 | 0.06 | −1.7 | ||

DJF | A | 128 | 25.6 | −0.31 | –0.16 | 6.8 | |

B | 130 | 25.0 | −0.33 | –0.74 | 3.2 | ||

MAM | A | 162 | 18.7 | 1.60 | 4.09 | * | −8.1 |

B | 159 | 23.3 | 0.50 | –0.55 | * | −3.0 | |

JJA | A | 245 | 21.8 | 0.48 | 0.97 | −3.0 | |

B | 252 | 21.6 | 0.12 | –0.42 | −5.5 | ||

SON | A | 146 | 23.5 | 0.56 | 0.95 | 1.4 | |

B | 158 | 26.5 | 0.94 | 1.37 | 1.8 |

**Table 8.**Selected statistical characteristics of mean annual (Ann) and seasonal (DJF, MAM, JJA, and SON) wind speed series in the Czech Republic in the 1961–1990 (A) and 1991–2020 (B) periods: means are in m s

^{−1}, coefficients of variation (CV) in %, linear trends in m s

^{−1}/10 years (in bold statistically significant at the 0.05 significance level). An asterisk * indicates statistically significant differences of a given characteristic between two 30-year periods.

Season | Period | Mean | CV | Skewness | Kurtosis | Slope | ||||
---|---|---|---|---|---|---|---|---|---|---|

Ann | A | 2.5 | * | 3.2 | * | −0.15 | * | −0.83 | 0.01 | * |

B | 2.3 | * | 5.7 | * | 0.62 | * | −0.46 | −0.12 | * | |

DJF | A | 2.9 | * | 9.7 | 0.52 | −0.02 | 0.07 | |||

B | 2.6 | * | 10.4 | 0.22 | −0.95 | −0.10 | ||||

MAM | A | 2.7 | * | 4.7 | * | −0.13 | * | 0.20 | −0.01 | * |

B | 2.5 | * | 7.6 | * | 1.26 | * | 1.17 | −0.10 | * | |

JJA | A | 2.1 | * | 6.3 | −0.17 | 0.63 | −0.03 | * | ||

B | 2.0 | * | 6.0 | 0.07 | 0.06 | −0.10 | * | |||

SON | A | 2.4 | * | 7.1 | 0.22 | −0.76 | 0.02 | * | ||

B | 2.2 | * | 8.2 | 0.32 | −0.22 | −0.13 | * |

**Table 9.**Pearson correlation coefficients of annual (Ann) and seasonal (DJF, MAM, JJA, and SON) series between sunshine duration (SD) and mean maximum temperatures (TMAX) and between mean air temperature (TAVG) and relative humidity (RH) in the CR during the 1961–2020, 1991–1990, and 1991–2020 periods. Statistically significant correlation coefficients at the 0.05 significance level are in bold.

Period | Ann | DJF | MAM | JJA | SON |
---|---|---|---|---|---|

SD versus TMAX | |||||

1961–2020 | 0.58 | 0.11 | 0.70 | 0.80 | 0.46 |

1961–1990 | 0.55 | 0.18 | 0.51 | 0.75 | 0.47 |

1991–2020 | 0.52 | 0.08 | 0.78 | 0.80 | 0.55 |

TAVG versus RH | |||||

1961–2020 | −0.67 | −0.28 | −0.57 | −0.77 | −0.04 |

1961–1990 | −0.39 | −0.12 | −0.27 | −0.54 | 0.11 |

1991–2020 | −0.62 | −0.22 | −0.58 | −0.84 | −0.22 |

**Table 10.**Linear trends of selected annual (Ann) and seasonal (DJF, MAM, JJA, and SON) series of circulation types and climatic variables (Var.) in 1961–2020 (a) in comparison with signs of linear trends (+ positive, − negative, 0 no trend) in two 30-year normal periods, 1961–1990 and 1991–2020 (b): ACT—anticyclonic circulation types (days/10 years), CCT—cyclonic circulation types (days/10 years), DCT—directional circulation types (days/10 years), SD—sunshine duration (hours/10 years), TAVG—mean temperature (°C/10 years), TMAX—mean maximum temperature (°C/10 years), TMIN—mean minimum temperature (°C/10 years), RH—relative humidity (%/10 years), P—precipitation (mm/10 years), WS—wind speed (m s

^{−1}/10 years). Bold figures and signs with an asterisk * indicate statistically significant trends at the 0.05 significance level.

Var. | Ann | DJF | MAM | JJA | SON | |||||
---|---|---|---|---|---|---|---|---|---|---|

a | b | a | b | a | b | a | b | a | b | |

ACT | 6.8 | + */+ | 1.7 | +/− | 1.9 | +/+ | 2.8 | + */+ | 0.0 | +/+ |

CCT | −4.3 | − */0 | −0.6 | −/+ | −2.1 | −/− | −1.4 | − */+ | 0.0 | −/0 |

DCT | −1.7 | 0/− | −0.9 | −/+ | 0.0 | +/− | −0.9 | 0/− | 0.0 | −/− |

SD | 16.8 | −/+ | −1.2 | +/− | 14.0 | +/+ | 10.5 | −/− | −7.1 | −/+ |

TAVG | 0.37 | +/+ * | 0.36 | +/+ | 0.36 | +/+ | 0.45 | +/+ * | 0.23 | −/+ * |

TMAX | 0.42 | +/+ * | 0.39 | +/+ | 0.49 | +/+ * | 0.52 | +/+ * | 0.21 | −/+ * |

TMIN | 0.35 | +/+ * | 0.38 | +/+ | 0.25 | +/+ | 0.40 | +/+ * | 0.27 | 0/+ * |

RH | −0.6 | −/− * | −0.5 | −/− | −1.2 | − */− * | −0.9 | −/− | 0.0 | −/− |

P | 5.5 | −/− | 1.6 | +/+ | −2.6 | −/− | 1.0 | −/− | 2.8 | +/+ |

WS | −0.07 | +/− * | −0.06 | +/− | −0.07 | −/− * | −0.05 | −/− * | −0.08 | +/− * |

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**MDPI and ACS Style**

Brázdil, R.; Zahradníček, P.; Dobrovolný, P.; Řehoř, J.; Trnka, M.; Lhotka, O.; Štěpánek, P. Circulation and Climate Variability in the Czech Republic between 1961 and 2020: A Comparison of Changes for Two “Normal” Periods. *Atmosphere* **2022**, *13*, 137.
https://doi.org/10.3390/atmos13010137

**AMA Style**

Brázdil R, Zahradníček P, Dobrovolný P, Řehoř J, Trnka M, Lhotka O, Štěpánek P. Circulation and Climate Variability in the Czech Republic between 1961 and 2020: A Comparison of Changes for Two “Normal” Periods. *Atmosphere*. 2022; 13(1):137.
https://doi.org/10.3390/atmos13010137

**Chicago/Turabian Style**

Brázdil, Rudolf, Pavel Zahradníček, Petr Dobrovolný, Jan Řehoř, Miroslav Trnka, Ondřej Lhotka, and Petr Štěpánek. 2022. "Circulation and Climate Variability in the Czech Republic between 1961 and 2020: A Comparison of Changes for Two “Normal” Periods" *Atmosphere* 13, no. 1: 137.
https://doi.org/10.3390/atmos13010137